On account of the sudden death of Professor Edward Forbes, who had engaged to furnish the article Geology for this work, it was found necessary to defer it to the present heading. Under Mineralogical Science, therefore, will be found first, Mineralogy properly so called; and secondly, Geology.

I.—MINERALOGY.

Mineralogy is sometimes understood as comprising the natural history of every portion of inorganic nature. Here we consider it as limited to the natural history of simple minerals or mineral species. In the strictest sense, a mineral species is a natural inorganic body, possessing a definite chemical composition, and assuming a regular determinate form or series of forms. This definition excludes many bodies often regarded as minerals: as, all the artificial salts of the chemists, all the inorganic secretions of plants and animals, all the remains of former living beings now imbedded in rocks. Some substances originally organic products have indeed, by common consent, found a place in mineral systems, as coal, amber, and mineral resins; but this is a departure from the strictness of the definition, and in most cases had perhaps better have been avoided. So also some amorphous substances, with no precise form or chemical composition, as some kinds of clay, have been introduced into works on mineralogy, but we believe often improperly, and with no beneficial result. Aggregates of simple minerals or rocks are likewise excluded from this science, though the various associations of minerals, their modes of occurrence, and their geological position, are important points in the history of the different species.

One most important object of a treatise on mineralogy should be to give such descriptions of minerals, their essential properties and distinctive characters, as will enable the student to distinguish the various species, and to recognise them when they occur in nature. But to accomplish this he must first become acquainted with the terminology or nomenclature of the science; that is, with the meaning of the terms used in describing these properties, and the various modifications they may undergo. With this is necessarily conjoined an account of the properties themselves, and of the more general laws by which their various changes are regulated. A second and closely-related portion of mineralogy is the system or classification, giving an account of the order in which the species are arranged, and the reasons for which it has been adopted. The third and most important part of mineralogy, to which these two are properly preparatory, is the physiography of the various species, giving an account of their characteristic marks, and a description of their appearance or external aspect and forms; their principal physical and chemical properties; their mode of occurrence, with their geological and geographical distribution; and their various uses, whether in nature or in the arts. Each of these departments will be considered in the following treatise in the order just mentioned.

PART I.—TERMINOLOGY.

CHAP. I.—FORM OF MINERALS.

The physical properties of a mineral comprise all those properties belonging to it as a body existing in space, and consisting of matter aggregated in a peculiar way. The more important of these are,—its form as shown in crystallization; its structure as determining its mode of cleavage and fracture; its hardness and tenacity; its weight or specific gravity; and its relations to light, heat, electricity, and magnetism.

Crystalline and Amorphous.—Mineral substances occur in two distinct modes of aggregation. Some consist of minute particles simply collected together, with no regularity of structure or constancy of external form, and are named amorphous. All fluid minerals are in this condition, together with some solid bodies, which appear to have condensed either from a gelatinous condition like opal, when they are named porodine, or from a state of igneous fluidity like obsidian and glass, when they are named hyaline. The other class have their ultimate atoms evidently arranged according to definite law, and are named crystalline, when the regularity of structure appears only in the internal disposition of the parts; and crystallized, when it also produces a determinate external form, or a crystal.

Faces, Edges, Angles, Axes of Crystals.—The word crystal in mineralogy designates a solid body exhibiting an original (not artificial) more or less regular polyhedric form. It is thus bounded by plane surfaces, named faces, which intersect in straight lines or edges, and these again meet in points and form solid angles, bounded by three or more faces. The space occupied by a crystal is often named a form of crystallization, which is thus the mathematical figure regarded as independent of the matter that fills it.

Crystals bounded by equal and similar faces are named simple forms; whilst those in which the faces are not equal and similar are named compound forms, or combinations, being regarded as produced by the union or combination of two or more simple forms. The cube or hexahedron (fig. 1), bounded by six equal and similar squares; the octahedron (fig. 2), by eight equilateral triangles; and the rhombohedron, by six rhombs,—are thus simple forms. An axis of a crystal is a line passing through its centre and terminating either in the middle of two faces, or of two edges, or in two angles; and axes terminating in similar parts of a crystal are named similar axes. In describing a crystal, one of its axes is supposed to be vertical or upright, and is then named the principal axis, and that axis is chosen which is the only one of its kind in the figure. A few other technical terms used in describing crystals will be explained as they occur.

Systems of Crystallization.—The forms of crystals that occur in nature seem almost innumerable. On examining them, however, more attentively, certain relations are discovered even between highly complex crystals. When the axes are properly chosen, and placed in a right position, the various faces are observed to group themselves in a regular and beautiful manner around these axes, and to be all so related as to compose connected series produced according to definite laws. In every mineral species there is a certain form of crystal from which, as a primary, every other form of crystal observed in that mineral species may be deduced. In each species the axes, bearing to each other definite numerical proportions, intersect at angles which are constant. So also the faces of the various forms are related to each other, and to their primary, according to certain definite laws. When viewed in this manner, and referred to their simplest forms, the innumerable variety of crystals occurring in nature may all be reduced to six distinct groups, or, as they are named, systems of crystallization. The following are the names given to these systems of crystallization in some of the best authors:

| Naumann | Mohs | Weiss and G. Rose | |---------|------|------------------| | 1. Tesseral System | Tessular | Regular | | 2. Tetragonal System | Pyramidal | 2 and 1 axial | | 3. Hexagonal System | Rhombohedral | 3 and 1 axial | | 4. Rhombo System | Orthotype | 1 and 1 axial | | 5. Monoclinohedric System | Hemiorthotype | 2 and 1 membered | | 6. Triclinohedric System | Anorthotype | 1 and 1 membered |

In the following treatise the terminology of Naumann is adopted, his method of classifying and describing crystals appearing the simplest and best adapted to promote the progress of the student.

Holohedric and Hemihedric.—Before describing these systems, it must be observed that certain crystals appear as the half of others, and are therefore named hemihedric; whilst the crystals with the full number of faces are named holohedric. Hemihedric crystals are formed when the alternate faces or groups of faces of a holohedric crystal increase symmetrically, so as to obliterate the other faces. Thus, if four alternate faces of the octahedron increase so as to obliterate the other four, a tetrahedron with half the number of faces is formed.

The first, or Tesseral System, named from tessera, a cube, which is one of the most frequent varieties, is characterized by three equal axes intersecting each other at right angles. Properly speaking, this system has no chief axis, as any one of them may be so named, and placed upright in drawing and describing the crystals. Of these there are thirteen varieties, which are thus classed and named from the number of their faces:

1. One Tetrahedron, or form with four faces. 2. One Hexahedron, with six faces. 3. One Octahedron, with eight faces. 4. Four Dodecahedrons, with twelve faces. 5. Five Icositetrahedrons, with twenty-four faces. 6. One Tetracontaoctahedron, with forty-eight faces.

The dodecahedrons are further distinguished, according to the form of their faces, into rhombic, trigonal, deltoid, and pentagonal dodecahedrons; and some of the icositetrahedrons have also received peculiar names.

The following is a description, with figures, of the different forms above mentioned, beginning with

The Holohedric forms.

1. The hexahedron or cube (fig. 1) is bounded by six equal squares, has twelve edges, formed by faces meeting at 90°, and eight trigonal angles. The principal axes join the centre points of any two opposite faces.—Examples are fluor spar, lead-glance, boracite.

2. The octahedron (fig. 2), bounded by eight equilateral triangles, has twelve equal edges, with planes meeting at 109° 28', and six trigonal angles. The principal axes join the opposite angles, two and two.—Example, alum, spinel, magnetic iron ore.

3. The rhombic-dodecahedron (fig. 3) is bounded by twelve equal and similar rhombs (diagonals as 1 and √2),

has twenty-four equal edges of 120°, and six trigonal and eight trigonal angles. The principal axes join two opposite trigonal angles.—Ex., garnet, red copper ore, boracite.

4. The tetrakisheptahedrons (variety of icositetrahedron, fig. 4), are bounded by twenty-four isosceles triangles, arranged in six groups of four each. They have twelve longer edges which correspond to those of the primitive or inscribed cube, and twenty-four shorter edges placed over each of its faces. The angles are eight hexagonal and six trigonal; the latter joined two and two by the three principal axes. This form varies in general aspect, approaching, on the one hand, to the cube; on the other, to the rhombic-dodecahedron.—Ex., fluor spar, gold.

5. The triakisoctahedrons (variety of icositetrahedron, fig. 5), are bounded by twenty-four isosceles triangles, in eight groups of three, and, like the previous form, vary in... general aspect from the octahedron on one side, to the rhombic-dodecahedron on the other. The edges are twelve longer, corresponding with those of the inscribed octahedron, and twenty-four shorter, three and three over each of the faces. The angles are eight trigonal and six ditetragonal (formed by eight faces); the latter angles joined two and two by the principal axes.—Ex., galena, diamond.

6. The icositetrahedrons (most common variety, fig. 6) are bounded by twenty-four deltoids or figures with four sides, of which two and two adjacent ones are equal. This form varies from the octahedron to the cube, sometimes approaching the former and sometimes the latter in general aspect. The edges are twenty-four longer and twenty-four shorter. The angles are six tetragonal joined by the principal axes, eight trigonal, and twelve rhombic, or tetragonal with unequal angles.

7. The hexakisoctahedrons (fig. 7), bounded by forty-eight scalene triangles, vary much in general aspect, approaching more or less to all the preceding forms; but most frequently they have the faces arranged either in six groups of eight, or eight of six, or twelve of four faces. There are twenty-four long edges, often corresponding to those of the rhombic-dodecahedron; twenty-four intermediate edges lying in pairs over each edge of the inscribed octahedron; and twenty-four short edges in pairs over the edges of the inscribed cube. There are six ditetragonal angles joined by the principal axes, eight hexagonal and twelve rhombic angles.—Ex., fluor spar, garnet, diamond.

The seven forms of crystals now described are related to each other in the most intimate manner. This will appear more distinctly from the following account of the derivation of the forms, with which is conjured an explanation of the crystallographic signs or symbols by which they are designated. We have adopted these symbols throughout this work, in the belief that they not only mark the forms in a greatly abbreviated manner, but also exhibit the relations of the forms and combinations in a way which words could hardly accomplish.

The derivation of forms is that process by which, from one form chosen for the purpose, and considered as the type—the fundamental or primary form—all the other forms of a system may be produced, according to fixed principles or general laws. In order to understand this process or method of derivation, the student should keep in mind that the position of any plane is fixed when the positions of any three points in it, not all in one straight line, are known. To determine the position, therefore, of the face of a crystal, it is only necessary to know the distance of three points in it from the centre of the crystal, or the points in which the face or its supposed extension would intersect the three axes of the crystal. The portion of the axes between this point and the centre are named parameters, and the position of the face is sufficiently known when the relative length or proportion of these parameters is ascertained. When the position of one face of a simple form is thus fixed or described, all the other faces are in like manner fixed, since they are all equal and similar, and all intersect the axes in a uniform manner; and the expression which marks or describes one face, marks and describes the whole figure.

The octahedron is generally adopted as the primary or fundamental form of the tesselar system, and distinguished by the first letter of the name, O. Its faces cut the half axes at equal distances from the centre; so that these semi-axes, or the parameters of the faces, have to each other the proportion $1:1:1$. In order to derive the other forms from the octahedron, the following construction is employed. The numbers refer to the descriptions above.

Suppose a plane so placed in each angle of the octahedron as to be vertical to the axis passing through that angle, and consequently parallel to the two other axes (or to cut them at an infinite distance = $\infty$); then the hexahedron or cube (1) is produced, designated by the crystallographic sign $\infty O \infty$; expressing the proportion of the parameters of its faces, or $\infty : \infty : \infty : 1$. If a plane is supposed placed in each edge parallel to one axis, and cutting the two other axes at equal distances, the resulting figure is the rhombic-dodecahedron (3), designated by the sign $\infty O$, the proportion of the parameters of its faces being $\infty : 1 : 1$. The triakisoctahedron (5) arises when on each edge of the octahedron planes are placed cutting the axis not belonging to that edge at a distance from the centre $m$ which is a rational number greater than 1. The proportion of its parameters is therefore $m : 1 : 1$, and its sign $mO$; the most common varieties being $2O$, $2O_2$, and $3O$. When, on the other hand, from a similar distance $m$ in each two semiaxes prolonged, a plane is drawn to the other semiaxis, or to each angle, an ikositetrahedron (6) is formed; the parameters of its faces have consequently the proportion $m : 1 : m$, and its sign is $mOm$; the most common varieties being $2O_2$ and $3O_3$, the former very frequent in leucite, analcime, and garnet. When, again, planes are drawn from each angle, or the end of one semiaxis of the octahedron, parallel to a second axis, and cutting the third at a distance $n$, greater than 1, then the tetrakisheptahedron (4) is formed, the parameter of its faces $\infty : 1 : n$; its sign $\infty On$; and the most common varieties in nature $\infty O_2$, $\infty O_2$, and $\infty O_3$. Finally, if in each semiaxis of the octahedron two distances, $m$ and $n$, be taken, each greater than 1, and $m$ also greater than $n$, and planes be drawn from each angle to these points, so that the two planes lying over each edge cut the second semiaxis belonging to that edge, at the smaller distance $n$, and the third axis at the greater distance $m$, then the hexakisoctahedron (7) is produced, the parameters, which are $m : n : 1$, its sign $mOn$, and the most common varieties $3O_3$, $4O_2$, and $5O_3$.

The next class of crystals are the semi-tesseral forms; and first, those with oblique faces, often named tetrahedral, from their relation to the tetrahedron. (1.) This form (fig. 8) is bounded by four equilateral triangles, has six equal edges with faces meeting at $70^\circ 32'$, and four trigonal angles. The principal axes join the middle points of each two op- posite edges.—Ex., gray-copper ore, boracite, and helvite.

(2.) The trigonal dodecahedrons (fig. 9) are bounded by twelve isosceles triangles, and vary in general form from the tetrahedron to the hexahedron. There are six longer edges corresponding to those of the inscribed tetrahedron, and twelve shorter, placed three and three over each of its faces; and four hexagonal and four trigonal angles.—Ex., gray-copper ore, and bismuth-blende. (3.) The deltoid-dodecahedrons (fig. 10) are bounded by twelve deltoids, and vary in general form from the tetrahedron on the one hand, to the rhombic-dodecahedron on the other. They have twelve longer edges lying in pairs over the edges of the inscribed tetrahedron; and twelve shorter edges, three and three over each of its faces. The angles are six tetra-

Fig. 10. Fig. 11.

gonal (rhombic), four acute trigonal, and four obtuse trigonal angles. The principal axes join two and two opposite rhombic angles.—Ex., gray-copper ore. (4.) The hexakistetrahe-

drons (fig. 11) are bounded by twenty-four scalene triangles, and most commonly have their faces grouped in four systems of six each. The edges are twelve shorter and twelve longer, lying in groups of three over each face of the inscribed tetrahedron, and twelve intermediate in pairs over its edges. The angles are six rhombic, joined in pairs by the principal axes, and four acuter and four ob-

tuser hexagonal angles.—Ex., diamond.

The derivation and signs of these forms are as follows:—

The tetrahedron arises when four alternate faces of the octahedron are enlarged, so as to obliterate the other four, and its sign is hence $\frac{O}{2}$. But, as either four faces may be thus enlarged or obliterated, two tetrahedrons can be formed similar in all respects except in position, and together making up the octahedron. These are distinguished by the signs $+$ and $-$, added to the above symbol, but only the latter in general expressed thus $-\frac{O}{2}$. In all hemihedral systems two forms similarly related occur, which may thus be named complementary forms. The trigonal dodecahedron is derived from the icositetrahedron by the expansion of the alternate trigonal groups of faces. Its sign is $\frac{mOm}{2}$, the most common variety being $\frac{202}{2}$, found in gray-copper ore. The deltoid-dodecahedron is in like manner the result of the increase of the alternate trigonal groups of faces of the triakisoctahedron, and its sign is $\frac{mO}{2}$. Lastly, the hexakis-

tetrahedron arises in the development of alternate hexa-

gonal groups of faces in the hexakisoctahedron, and its sign is $\frac{mOn}{2}$.

The parallel-faced semitesseral forms are two. (1.) The pentagonal dodecahedrons (fig. 12) are bounded by twelve symmetrical pentagons, and vary in general aspect between the hexahedron and rhombic-dodecahedron. They have six regular (and in general longer) edges, lying over the faces of the inscribed hexahedron, and twenty-four generally shorter (seldom longer) edges, usually lying in pairs over its edges. The angles are eight of three equal

angles, and twelve of three unequal angles. Each principal axis unites two opposite regular edges. This form is derived from the tetrakisheptahedron, and its sign is $\frac{\infty On}{2}$, one of the most common varieties being $\frac{\infty O2}{2}$, found frequently in iron pyrites and cobaltine. (2.) The dyakisdodecahe-

dron (fig. 13), bounded by twenty-four trapezoids with two sides equal, has twelve short, twelve long, and twenty-four intermediate edges. The angles are six equiangular rhombic, united in pairs by the principal axes, eight trigonal, and twenty-four irregular tetragonal angles. It is derived from the hexakisoc-

hedron, and its sign is $\left[\frac{mOn}{2}\right]$, the brackets being used to distinguish it from the hexakis-

tetrahedron, also derived from the same primary form. It occurs in iron pyrites and cobaltine. There are two other tetrahe-

dral forms, the pentagonal dodecahedron (fig. 14), and the pentagonal icositetrahedron (fig. 15), both bounded by irregular pentagons, but not yet observed in nature.

Combinations.—These forms of the tesseral system (and Combin-

this is true also of the five other systems of crystallization), tions, not only occur singly, but often two, three, or more united in the same crystal, forming what are named combinations. In this case it is evident that no one of the individual forms can be completely developed, because the faces of one form must partially interfere with the faces of the other forms. A combination therefore implies that the faces of one form shall appear symmetrically disposed between the faces of other forms, and consequently in the room of certain of their edges and angles. These edges and angles are thus, as it were, cut off, and new ones produced in their place, which properly belong neither to the one form nor the other, but are edges or angles of combination. Usually, one form predominates more than the others, or has more influence on the general aspect of the crystal, and hence is distinguished as the predominant form, the others being named subordinate.

The following terms used on this subject require explana-

tion. A combination is developed when all the forms con-

tributing to its formation are pointed out; and its sign con-

sists of the signs of these forms, written in the order of their influence on the combination, with a point between. An angle or edge is said to be replaced when it is cut off by one or more secondary planes; it is truncated when cut by one plane, forming equal angles with the adjacent faces; and an edge is bevelled when replaced by two planes, which are equally inclined to the adjacent faces.

It will be readily seen that such combinations may be exceedingly numerous, or rather infinite; and only a few of the more common can be noticed, simply as specimens of the class. Many others more complicated will occur in the descriptive part of this treatise. Among pentatesseral combinations, the cube, octahedron, and also the rhombic-dodecahedron, are the predominant forms. In fig. 16 the cube has its angles replaced by the faces of the octahedron, and the sign of this combination is $\infty O \infty$. In fig. 17 this process may be regarded as having proceeded still further, so that the faces of the octahedron now predominate, and the sign of the same two elements but in reverse order is $O \infty O \infty$. In fig. 18 the cube has its edges replaced by the faces of the rhombic-dodecahedron, the sign being $\infty O \infty$, whilst in fig. 19 there is the same combination, but with the faces of the cube subordinate, and hence the symbol is $\infty O \infty O \infty$. The former figure, it will be seen, has more the general aspect of the cube; the latter of the dodecahedron.

In combinations of semitesseral forms with oblique faces, the tetrahedron, the rhombic-dodecahedron, or even the hexahedron, seldom a trigonal-dodecahedron, are the more common predominant forms. In fig. 20 two tetrahedrons in opposite positions, $\frac{O}{2} - \frac{O}{2}$, are combined. In fig. 21 a very complex combination of seven forms is represented in a crystal of grey-copper ore, its full sign being—

The letters in brackets connecting them with the respective faces of the figure. As examples of combinations of semitesseral forms with parallel faces, we may take fig. 22, in which each of the angles of the cube is unsymmetrically replaced by three faces of the dyakisdodecahedron, and hence $\infty O \infty \cdot \left[ \frac{4O^2}{2} \right]$; or fig. 23, in which the pentagonal-dodecahedron has its trigonal angles replaced by the faces of the octahedron, consequently with the sign $\infty O \infty \cdot \frac{O}{2}$. Figure 24 represents the same combination but with greater predominance of the faces of the octahedron, the crystal being bounded by eight equilateral and twelve isosceles triangles.

**Tetragonal System.**—This system has three axes at right angles, two of them equal and one unequal. The last is the principal axis, and when it is brought into a vertical position the crystal is said to be placed upright. Its ends are named poles, and the edges connected with them polar edges. The two other axes are named subordinate or lateral axes, and a plane passing through them is named the basis of the crystal. The two planes that pass through the principal and one of the lateral axes are named normal chief sections, and a plane through the chief axis intermediate to them a diagonal chief section. The name tetragonal is derived from the form of the basis, which is usually quadratic.

There are eight tetragonal forms, of which five are closed,—that is, bounded on all sides by planes, and of definite extent; and three open, which in certain directions are not bounded, and consequently of indefinite extent.

The description of the varieties is as follows, it being premised that a crystallographic pyramid is equivalent to two geometrical pyramids joined base to base. **Closed forms.**—(1.) Tetragonal pyramids (figs. 25, 26) are inclosed by eight isosceles triangles, with four middle edges all in one plane, and eight polar edges. There are three kinds of this form, distinguished by the position of the lateral axes. In the first these axes unite the opposite angles; in the second they intersect the middle edges equally; and in the third they lie in an intermediate position, or divide these edges unequally; the latter being hemihedral forms. These pyramids are also distinguished as obtuse (fig. 25) or acute (fig. 26), according as the vertical angle is greater or less than in the octahedron, which, though intermediate, is never a tetragonal form. (2.) Ditetragonal pyramids (fig. 27) are bounded by sixteen scalene triangles, whose base lines are all in one plane. This form rarely occurs except in combinations. (3.) Tetragonal sphenoids (fig. 28), bounded by four isosceles... triangles, are the hemihedral forms of the first variety of tetragonal pyramids. (4.) The tetragonal scalenohedron (fig. 29), bounded by eight scalene triangles, whose bases rise and fall in a zig-zag line, is the hemihedral form of the ditetragonal pyramid. The latter two forms are rare.

Open forms.—Tetragonal prisms (fig. 30) bounded by four planes parallel to the principal axis; ditetragonal prisms by eight similar planes. In these prisms the principal axis is supposed to be prolonged infinitely, or to be unbounded. Where it is very short and the lateral axes infinite, the basal pinacoid is formed, consisting merely of two parallel faces.

The various series of tetragonal crystals are distinguished from each other only by their relative dimensions. To determine these, one of the series must be chosen as the fundamental form, and for this purpose a tetragonal pyramid of the first variety, designated by \( P \) as its sign, is selected. The angle of one of its edges, especially the middle edge, found by measurement, determines its angular dimensions; whilst the proportion of the principal axis (\( a \)) to the lateral axes supposed equal to 1, gives its linear dimensions. The parameters, therefore, of each face of the fundamental form are \( 1 : 1 : a \).

Now if \( m \) be any (rational) number, either less or greater than one, and if from any distance \( ma \) in the principal axis planes be drawn to the middle edge of \( P \), then new tetragonal pyramids of the first kind, but more or less acute or obtuse than \( P \), are formed. The general sign of these pyramids is \( mP \), and the most common varieties \( \frac{1}{2}P \), \( 2P \), \( 3P \); with the chief axis equal to \( \frac{1}{2} \), twice or thrice that of \( P \). If \( m \) becomes infinite, or \( = \infty \), then the pyramid passes into a prism, indefinitely extended along the principal axis, and with the sign \( \infty P \); if \( m = 0 \), which is the case when the lateral axes are supposed infinite, then it becomes a pinacoid, consisting properly of two basal faces open towards the lateral axes, and designated by the sign \( 0P \). The ditetragonal pyramids are produced by taking in each lateral axis distances \( n \) greater than 1, and drawing two planes to these points from each of the intermediate polar edges. The parameters of these planes are therefore \( m : 1 : n \), and the general sign of the form \( mPn \), the most common values of \( n \) being \( \frac{1}{2}, 2, 3, \) and \( \infty \). When \( n = \infty \), a tetragonal pyramid of the second kind arises, designated generally by \( mP\infty \), the most common in the mineral kingdom being \( P\infty \) and \( 2P\infty \). The relation of these to pyramids of the first kind is shown in fig. 31, where \( ABBBX \) is the first, and \( ACCCX \) the second kind of pyramid. In like manner from the prism \( \infty P \), the ditetragonal prisms \( \infty Pn \) are derived, and finally when \( n = \infty \), the tetragonal prism of the second kind, whose sign is \( \infty P\infty \).

The combinations of the tetragonal system are either holohedral or hemihedral; but the latter are rare. Prisms and pinacoids must always be terminated on the open sides by other forms. Thus in fig. 32 a square prism of the first kind is terminated by the primary pyramid, and has its lateral angles again replaced by another more acute pyramid of the second kind, so that its sign is \( \infty P \cdot P \cdot 2P\infty \). In fig. 33 a prism of the second kind is first bounded by the fundamental pyramid, and then has its edges of combination replaced by a ditetragonal pyramid, and its sign is here \( \infty P\infty \cdot P \cdot 3P3 \). In fig. 34 the polar edges of the pyramid are replaced by another pyramid, its sign being \( P \cdot P\infty \). In fig. 35 a hemihedral form very characteristic of copper pyrites is represented, \( P \) and \( P' \) being the two spinoids, \( a \) the basal pinacoid, and \( b, c \), two ditetragonal pyramids.

The Hexagonal System.—The essential character of this system is, that it has four axes,—three equal lateral axes intersecting each other in one plane at 60°, and one principal axis at right angles to them. The extremities of the principal axis are named poles, and sections through it and one lateral axis, normal chief sections. The plane through the lateral axes is the basis, and from its hexagonal form gives the name to the system. As in the last system, its forms are either closed or open; and are divided into holohedral, hemihedral, and tetratohedral,—the last, forms with only a fourth part of their faces developed. The tetratohedral and many of the hemihedral forms are of rare occurrence, and only a few of the more common require to be here described.

The hexagonal pyramids (figs. 36, 37) are bounded by twelve isosceles triangles, and are of three kinds, according as the lateral axes fall in the angles, in the middle of the lateral edges, or in another point of these edges, the latter being hemihedral forms. They are also classed as acute or obtuse, but without any very precise limits. The trigonal pyramid is bounded by six triangles, and may be viewed as the hemihedral form of the hexagonal. The dihexagonal pyramid is bounded by twenty-four scalene triangles, but has never been observed alone, and rarely even in combinations. The more common prisms are the hexagonal of six sides, and the dihexagonal of twelve sides.

As the fundamental form of this system, a particular pyramid \( P \) is chosen, and its dimensions determined either from the proportion of the lateral to the principal axis \( (1 : a) \), or from the measurement of its angles. From this form \( (mP) \) others are derived exactly as in the tetragonal system. Thus dihexagonal pyramids are produced with the general sign \( mPn \), the chief peculiarity being that, whereas in the tetragonal system \( n \) might have any rational value from 1 to \( \infty \), in the hexagonal system it can only vary from 1 to 2, in consequence of the geometric character of the figure. When \( n = 2 \) the dihexagonal changes into an hexagonal pyramid of the second kind, whose sign is \( mP2 \). When \( m = \infty \) various prisms arise from similar changes in the value of \( n \); and when \( m = 0 \) the basal pinacoid.

Few hexagonal mineral species form perfect holohedral combinations. Though quartz and apatite appear as such, yet properly the former is a tetrartohedral, the latter a hemihedral species. In holohedral species the predominant faces are usually those of the two hexagonal prisms \( \alpha P \) and \( \alpha P2 \) or of the pinacoid \( OP \); whilst the pyramids \( P \) and \( 2P2 \) are the most common subordinate forms. Figure 38 represents the prism, bounded on the extremities by two pyramids; one, \( P \), forming the point, the other \( 2P2 \) the rhombic faces on the angles, or \( \alpha P, P, 2P2 \). In some crystals the lateral edges of the prism are replaced by the second prism \( \alpha P2 \), producing an equiangular twelve-sided prism, which always represents the combination \( \alpha P, \alpha P2 \), and cannot occur as a simple form. An example of a more complicated combination is seen in fig. 39, of a crystal of apatite, whose sign with the corresponding letters is \( \alpha P(M), \alpha P2(e), OP(P), \frac{1}{2}P(r), P(x), 2P(z), P2(a), 2P2(s), 4P2(d) \).

Hexagonal minerals more frequently crystallize in those series of hemihedral forms that are named rhombohedral, from the prevalence in them of rhombohedrons. These are (fig. 40) bounded by six rhombs, whose lateral edges do not lie in one plane, but rise and fall in a zig-zag manner. The principal axis unites the two trigonal angles, formed by three equal plane angles, and in the most common variety the secondary axes join the middle points of two opposite edges. When the polar edges form an angle of more than 90° the rhombohedrons are named obtuse; when of less, acute. Hexagonal scalenohedrons (figure 41) are bounded by twelve scalene triangles, whose lateral edges do not lie in one plane. The principal axis joins the two hexagonal angles, and the secondary axis the middle points of two opposite lateral edges.

The rhombohedron is derived from the first kind of hexagonal pyramid by the hemihedral development of its alternate faces. Its general sign should therefore be \( \frac{mP}{2} \); but on several grounds it is found better to designate it by \( R \) or \( mR \), and its complimentary figure by \( -mR \). When the prism or pinacoid arise as its limiting forms, they are designated by \( \alpha R \) and \( OR \), though in no respect changed from the limiting forms \( \alpha P \) and \( OP \) of the pyramid. The scalenohedron is properly the hemihedral form of the dihexagonal pyramid, but is better derived from the inscribed rhombohedron \( mR \). If the halves of the principal axis of this are multiplied by a definite number \( n \), and then planes drawn from the extremities of this enlarged axis to the lateral edges of the rhombohedron, as in figure 42, the scalenohedron is constructed. Hence it is designated by \( mR^n \), the \( n \) being written on the right hand, like an algebraic exponent; and the dihexagonal prism is in like manner designated by \( \alpha R^n \).

The combinations of rhombohedral forms are very numerous, some hundreds being described in calc-spar alone. Among the more common is the prism in combination with a rhombohedron, as in the twin crystal of calc-spar (fig. 43), with the sign \( \alpha R, -\frac{1}{2}R \), the lower half being the same form with the upper, but turned round 180°. In figure 44, the rhombohedron \( mR \) has its polar edges replaced by another rhombohedron \( -\frac{1}{2}mR \); and in figure 45 its lateral edges bevelled by the scalenohedron \( mR^n \). A more com- plex combination of five forms is represented in the crystal of calc-spar, fig. 46, its sign with the letters on the faces being $R(y) \cdot R(r) \cdot R(P) \cdot 4R(m) \cdot \infty R(c)$. Tetartohedric combinations are seen most distinctly in pure quartz or rock-crystal, the pyramids of the first kind appearing as rhombohedrons, those of the second kind as trigonal pyramids, the dihexahedral prisms are ditrigonal prisms, and the prism $\infty P_2$ as a trigonal prism. Most of these forms, however, occupy but a very subordinate place in the combinations which consist essentially of the prism $\infty P$, and the rhombohedron $R = \frac{P}{4}$.

**Rhombic System.**—The rhombic system is characterized by three axes, all unequal, but at right angles to each other. One of these is assumed as the chief axis, when the others are named subordinate. The plane passing through the secondary axes or the basis forms a rhomb, and from this name is derived. This system comprises only a few varieties of forms that are essentially distinct, and its relations are consequently very simple.

The closed forms are,—(1st.) The rhombic pyramids (figs. 47, 48), bounded by eight scalene triangles, whose lateral edges lie in one plane, and form a rhomb. They have eight polar edges,—four acute and four more obtuse,—and four lateral edges, and six rhombic angles, the most acute at the extremities of the longest axis. (2d.) The rhombic sphenoids (fig. 49) are bounded by four scalene triangles with their lateral edges not in one plane; and are a hemihedral form of the rhombic pyramid of unfrequent occurrence. The open forms again are, (3d.) Rhombic prisms bounded by four planes parallel to one of the axes which is indefinitely extended. They are divided into upright and horizontal prisms, according as either the principal or one of the lateral axes is supposed to become infinite. For the latter form the name dome or dome has been used; and two kinds, the macrodome and the brachydome, have been distinguished. Rhombic pinacoids also arise when one axis becomes = 0, and the two others are indefinitely extended.

In deriving these forms from a primary, a particular rhombic pyramid $P$ is chosen, and its dimensions determined either from the angular measurement of two of its edges, or by the linear proportion of its axes $a : b : c$; the greater lateral axis $b$ being assumed equal to 1. To the greater lateral axis the name macrodiagonal is frequently given; to the shorter, that of brachydiagonal; and the two principal sections are in like manner named macrodiagonal and brachydiagonal, according to the axis they intersect. The same terms are applied throughout all the derived forms, where they consequently mark only the position of the faces in respect to the axes of the fundamental crystal, without reference to the relative magnitude of the derived axes.

By multiplying the principal axis by any rational number $m$, greater or less than 1, a series of pyramids arise, whose general sign is $mP$, and their limits the prism and pinacoid, the whole series being contained in this formula, $OP - mP - P - mP - \infty P$; which is the fundamental series, the lateral axes always remaining unchanged.

From each member a new series may, however, be developed in two directions by increasing one or other of the lateral axes. When the macrodiagonal is thus multiplied by any number $n$ greater than 1, and planes drawn from the distance $n$ to the polar edges, a new pyramid is produced, named a macropyrainid, with the sign $nP$, the mark over the $P$ pointing out the axis enlarged. When $n = \infty$, a macrodome results, with the sign $mP\infty$. If the shorter axis is multiplied, then brachypyramids and brachydomes are produced with the signs $mPn$ and $mP\infty$. So also from the prism $\infty P$, on the one side, numerous macroprisms $nPn$, with the limiting ma- crocinacoid $\alpha P\infty$; on the other, numerous brachyprisms $\alpha P_n$, with the limit form $\alpha P\infty$, or the brachypinacoid.

In figs. 50, 51, the two domes are shown in their relation to the primitive pyramid.

The pyramids seldom occur independent, or even as the predominant forms in a combination,—sulphur, however, being an exception. Prisms or pinacoids usually give the general character to the crystal, which then appears either in a columnar or tabular, or even in a rectangular pyramidal form. The determination of the position of these crystals, as vertical or horizontal, depends on the choice of the chief axis of the fundamental form. In the topaz crystal (fig. 52) the brachyprism and the pyramid are the predominant elements, associated with the prism, its sign and letters being $\alpha P_2(l) \cdot P(o) \cdot \alpha P(m)$. Fig. 53 of stilbite is another example, the macropinacoid $\alpha P\infty$ or $M$, being combined with the pyramid $P(r)$, the brachypinacoid $\alpha P\infty(T)$, and the basal pinacoid $OP(P)$.

Another instance is fig. 54 of a lievrite crystal, where the brachyprism and pyramid combine with the macrodome, or $\alpha P_2 \cdot P \cdot P\infty$.

The following figures are very common forms of barytes; figs. 55 and 56 being both composed of the pinacoid, a brachydome and macrodome with sign $OP(c) \cdot P\infty(f)$ $\frac{1}{2}P\infty(d)$, the variation in aspect arising from the predominance of different faces; and fig. 57 consisting of the macrodome $\frac{1}{2}P\infty$, the prism $\alpha P(g)$, and the pinacoid $OP$.

**The Monoclinohedric System.**—This system is characterized by three unequal axes, two of which intersect each other at an oblique angle, and are cut by the third at right angles. One of the oblique axes is chosen as the chief axis, and the other axes are then distinguished as the orthodiagonal (right-angled), and clinodiagonal (oblique-angled). The same terms are applied to the chief sections, and the name of the system refers to the fact that these two planes and the base, together with two right angles, form also one oblique angle $C$.

The forms of this system approach very near to those of the rhombic series, but the inclination of the axes, even when almost a right angle, gives them a peculiar character, by which they are always readily distinguished. Each pyramid thus separates into two altogether independent forms or hemipyramids. Three varieties of prism also occur—vertical, inclined, and horizontal—with faces parallel to the chief axis, the clinodiagonal or the orthodiagonal. The horizontal prisms, like the pyramids, separate into two independent partial forms, named hemiprisms or hemidomes. The inclined prisms are often designated clinodomes, the term prism being restricted to the vertical forms. Orthopinacoids and clinopinacoids are also distinguished from their position in relation to the axes.

The monoclinohedric pyramids (fig. 58) are bounded by eight scalene triangles of two kinds, four and four only being similar. Their lateral edges lie all in one plane, and the similar triangles are placed in pairs on the clinodiagonal polar edges. The two pairs in the acute angle between the orthodiagonal and basal section are designated the positive hemipyramid; whilst the two pairs in the obtuse angles of the same sections form together the negative hemipyramid. But as these hemipyramids are wholly independent of each other, they are rarely observed combined. More frequently each occurs alone, and then forms a prism-like figure, with faces parallel to the polar edges, and open at the extremities. Hence, like all prisms, they can only appear in combination with other forms. The vertical prisms are bounded by four equal faces parallel to the principal axis, and the cross section is a rhomb; the clinodomes have a similar form and section; whilst the horizontal prisms or domes have unequal faces, and their section is a rhomboid.

The mode of derivation of these forms closely resembles that of the rhombic series. A complete pyramid is assumed as the fundamental form, and designated $\pm P$, in order to express the two portions of which it consists. Its dimensions are given when the proportion of its axes $a : b : c$, and the angular inclination of the oblique axes $C$, which is also that of the orthodiagonal section to the basis, are known. The fundamental series of forms is, $OP \ldots \pm mP \ldots \pm P \ldots \pm mP \ldots \pm P$; from each of whose members, by changing the dimensions of the other axes, new forms may be again derived. Thus from $\pm mP$, by multiplying the orthodiagonal by any number $n$, a series of orthopyramids $\pm mP_n$ is produced, with the orthodomes $\pm mP\infty$ as limiting forms. The clinodiagonal produces a similar series, distinguished from the former by the sign being put in brackets, thus, $(mP_n)$, with the limiting clinodome $(mP\infty)$ always completely formed, and therefore without the signs $\pm$ attached. From $\alpha P$ arise ortho-prisms $\alpha P_n$, and the orthopinacoid $\alpha P\infty$; and clinoprism $(\alpha P_n)$, and the clinopinacoid $(\alpha P\infty)$.

The combinations of this system may be easily understood from their resemblance to those of the rhombic; the chief difficulty being in the occurrence of partial forms, which, however, closely resemble the hemihedric forms of the previous systems. We shall therefore only select a few examples frequently observed in the mineral kingdom.

Fig. 59 represents a very common form of gypsum crystals \((\infty P \infty) (P) \cdot \infty P(f) \cdot P(b)\). The most common form of augite is represented in fig. 60, with the sign \(\infty P \infty (r) \cdot (\infty P \infty) (l) \cdot P(s)\). Fig. 61 is a crystal of common felspar or orthoclase, composed of the clinopinacoid \((\infty P \infty) (M)\), the prism \(\infty P(T)\), the basal pinacoid \(0P(P)\), and the hemidomes \(2P \infty(y)\): to which, in fig. 62 of the same mineral, the hemipyramid \(P(o)\), and the clinocone \((2P \infty)(n)\), are added.

**Triclinohedric System.**—This is the least regular of all the systems, and departs the most widely from symmetry of form. The axes are all unequal, and inclined at angles none of which are right angles, so that to determine any crystal or series of forms the proportion of the axes \(a : b : c\), and also their angles, or those of the inclination of the chief sections, must be known. As in the previous system, one axis is chosen as the principal axis, and the two others distinguished as the macrodiagonal and brachydiagonal axes. In consequence of the oblique position of the principal sections, this system consists entirely of partial forms wholly independent on each other, and each composed only of two parallel faces. The complete pyramid is thus broken up into four distinct quarter pyramids, and the prism into two hemiprisms. Each of these partial forms is thus nothing more than a pair of parallel planes, and the various forms consequently mere individual faces. This circumstance renders many triclinohedric crystals very unsymmetrical in appearance.

Triclinohedric pyramids (fig. 63) are bounded by eight triangles, whose lateral edges lie in one plane. They are equal and parallel two and two to each other; each pair forming, as just stated, a tetartopyramid or open form, only limited by combination with other forms, or, as we may suppose, by the chief sections. The prisms are again either vertical or inclined; the latter named domes, and their section is always rhomboidal. In deriving the forms, the fundamental pyramid is placed upright with its brachydiagonal axis to the spectator, and the partial forms designated, the two upper by 'P and P', the two lower by P and P', as in the figure. The further derivation now follows as in the rhombic system, with the modifications already mentioned, so that we need not delay on it longer, especially as the minerals crystallizing in these forms are not numerous.

Some combinations of this system, as the series exhibited by most of the felspars, approach very near to the monoclinohedric system; whilst others, as the blue copper, or vitriol, and axinite, show great incompleteness and want of symmetry. In the latter case the determination of the forms is often difficult and requires great attention. As specimens, we may notice the albite crystal (fig. 64), in which \(P\) is the basal pinacoid \(0P\), \(M\) the brachydiagonal pinacoid \(\infty P \infty\), \(s\) the upper right pyramid \(P'\), \(l\) the right hemiprism \(\infty P\), \(T\) the left hemiprism \(\infty P\); and \(x\) the hemidome \(2P \infty\). Figures 65 and 66 are crystals of axinite, the former from Dauphiné, the latter very common in Cornwall, of whose faces the following is the development,—\(r\) the macropinacoid \(\infty P \infty\); \(P\) the left hemiprism \(\infty P\); \(u\) the left upper quarter pyramid \(P\); \(l\) the left upper quarter pyramid \(2P\); \(s\) the left upper partial form of the macropyramid \(3P\); and \(x\) the hemidome \(2P \infty\).

**Imperfections of Crystals.**

In the foregoing description of the forms of crystals the planes have been supposed smooth and even, the faces equal and uniform, or at the same distance from the centre or point of intersection of the axes, and each crystal also perfect or fully formed and complete on every side. In nature, however, these conditions are rarely if ever realized, and the edges of crystals are seldom straight lines, or the faces mathematical plane surfaces. A very interesting variety of these irregularities, which pervades all the systems except the tesserall, is named **hemimorphism**. In this the crystals are bounded on the opposite ends of their chief axis by faces belonging to distinct forms, and hence only the upper or under half of each form is produced, or the crystal, as the name implies, is half-formed. Figure 67 represents a common variety of tourmaline, bounded on the upper end by the planes of the rhombohedrons \(R\) and \(-2R\), and on the lower end by the basal pinacoid. In fig. 68 of electric calamine the upper extremity shows the basis \(k\). two brachydomes o and p; and two macrodomes m and l; whilst on the lower end it is bounded by the faces P of the primary form. This appearance becomes more interesting from the fact, that most hemihemorphic crystals acquire polar electricity from heat,—that is, exhibit opposite kinds of electricity at opposite ends of the crystal.

The faces of crystals are very frequently rendered imperfect by striæ or minute linear and parallel elevations and depressions. These arise in the oscillatory combination of two crystal forms, alternately prevailing through small spaces. The striæ, therefore, are in reality the edges of combined forms. They are very common on quartz, sorth, and some other minerals; and frequently indicate combinations where only a simple form would otherwise appear to exist. The cubes and pentagonal dodecahedrons of iron pyrites are frequently striated, and in three directions at right angles to each other. In calc-spar the faces of the rhombohedron, $-\frac{1}{2}R$ (q in fig. 43 above) are almost never without striæ parallel to the oblique diagonal. The striation is said to be simple when only one series of parallel lines appears on each face, or feathered when two systems diverge from a common line. In other crystals the faces, then said to be drusey, are covered by numerous projecting angles of smaller crystals; an imperfection often seen in flour spar. The faces of crystals occasionally appear curved either as in tourmaline and beryl from the peculiar oscillatory combination mentioned, or by the union of several crystals at obtuse angles, like stones in a vault, as in stilbite and prehnite. A true curvature of the faces probably occurs in the saddle-shaped rhombohedrons of brown spar and iron spar, in the lens-like crystals of gypsum, and in the curved faces so common on diamond crystals. In chabasite similar curved faces occur, but concave. In galena and augite the crystals are often rounded on the corners as if by an incipient state of fusion. On other crystals the faces are rendered uneven from inequalities following no certain rule. These imperfections furnish valuable assistance in developing very complex combinations, all the faces of each individual form being distinguished by the same peculiarity of surface.

Irregularities in the forms of crystals are produced when the corresponding faces are placed at unequal distances from the centre, and consequently differ in form and size. Thus the cubes and octahedrons of iron pyrites, galena, and fluor spar, are often lengthened along one axis. Quartz is subject to many such irregularities, which are seen in a very remarkable manner on the beautiful transparent and sharply angular crystals from Dauphine. In such irregular forms, instead of one line, the axes are then represented by an infinite number of lines, parallel to the ideal axis of the figure. The same irregularity carried to a greater extent frequently causes certain faces required for the symmetry of the form, altogether to disappear. Again, some crystals do not fill the space marked out by their outline, holes and vacancies being left in the faces, occasionally to such an extent that they seem little more than mere skeletons. This appearance is very common on crystals produced artificially, as in common salt, alum, bismuth, silver, &c. A perfect crystal can only be produced when during its formation it is completely isolated, so as to have full room to expand on every side. Hence the most perfect crystals have been originally imbedded singly in some uniform rock mass. Next to them in perfection are forms that grow singly on the surface of some mass of similar or distinct composition, especially when the point of adherence is small. An incompleteness of form, or at least a difficulty in determining it, arises from the minuteness of some crystals, or from their contracted dimensions in certain directions. Thus some appear mere tabular, or lamellar planes, whilst others run out into acicular, needle-shaped, or capillary crystals. Amid all these modifications of the general form of the crystal, of the condition and aspect of its individual faces, or of its linear dimensions, one important element, the angular measurement, remains constant. In some monoxial crystals, indeed, increase of temperature produces an unequal expansion in different directions, slightly changing the relative inclination of the faces, but so small as to be scarcely perceptible in common measurements, and hence producing no ambiguity. More important are the angular changes which in many species accompany slight changes in chemical composition, particularly in the relative proportions of certain isomorphous elements. But notwithstanding these limitations of the great truth of the permanence of the angular dimensions of crystals, announced by Romé de l'Isle, remains unaffected; only, as Mohs well states, it must not be interpreted with a rigid immutability, inconsistent with the whole analogy of other parts of nature.

The Goniometer and Measurement of Crystals.

The fact just stated of the permanence of the angular dimensions of crystals shows the importance of some accurate method of measuring their angles; that is, the inclination of two faces to each other. Two instruments have been specially used for this purpose,—the common or contact goniometer, invented by Caringean, and the reflecting goniometer of Wollaston. The former is simply two brass rulers turning on a common centre, between which the crystal is so placed that its faces coincide with the edges of the rulers, and the angle is then measured on a graduated arc. This instrument is sufficiently accurate for many purposes and for large crystals; but for precise determination is far inferior to the reflecting goniometer. This requires smooth and even faces, but these may be very small, even the hundredth of an inch, in skilful hands; and as small crystals are generally most perfect, far greater accuracy can be attained, and the measurement depended on to one minute ($\frac{1}{60}$).

The reflecting goniometer is represented in the annexed figure. It consists essentially of a graduated circle mm, divided on its edge into twice 180°, or more often into half degrees, the minutes being read off by the vernier kk. This circle turns on an axis connected with t, so that by turning this the circle is moved round, but stopped at 180°, when moving in one direction, by a spring at k. The other part of the instrument is intended to attach and adjust the crystal to be measured. The first axis of mm is hollow, and a second axis, aa, passes through it from ss, so that this and all the connected parts from b to f can be turned without moving the circle mm. The axis d passes through a hole in bc, so that it can turn the arm de into any required position; f is a similar axis turning the arm og; and pg a fourth axis, in like manner moveable in g, and with a small knob at q, to which the crystal to be measured is attached.

When about to use the instrument it should be placed on a table, with its base horizontal, which is readily done by the screws in it; and opposite to a window at about 12 or 15 feet distance, so that its axis shall be parallel to the horizontal bars of the window. One of the upper bars of the window, and also the lower bar, or, instead of the latter, a white line on the floor or table parallel to the window, should then be chosen in order to adjust the crystal. The observer places himself behind the instrument with the side \(a\) at his right hand. The crystal is then attached to \(q\) by a piece of wax with the two faces to be measured upwards. The axis \(f_0\) is made parallel to \(aa\), and the eye being brought near to the first face of the crystal, the axes \(aa\) and \(p\) are turned till the image of the window is seen reflected in the face with the horizontal and vertical bars in their position. The axis \(d\) is then turned through a considerable angle (say 60°), and the image of the window again sought and brought into its proper place by turning the axis \(f\), without moving \(p\). When this is done that face is brought into its true position, normal to \(d\), so that no motion of \(d\) can disarrange it. Hence the image of the window may now be sought in the second face and brought into its true position, with the horizontal bars seen horizontal, by moving the axes \(d\) and \(a\). When this is done the crystal is properly adjusted, and the angle is thus measured. First bring the zero of the circle and vernier to coincide, and then turn the inner axis \(a\) or \(ss\), and move the eye till the image of the upper bar of the window reflected from the more distant face of the crystal coincides with the lower bar or horizontal line seen directly. Keeping the eye in its place, turn the outer axis \(tt\) till the reflected image of the upper bar in the other face in like manner coincides with the lower line, and the angle of the two faces is then read off on the divided circle. As the angle measured is not directly that of the faces, but of the rays of light reflected from them, or the difference of the angle wanted from 180°, the circle has the degrees numbered in the reverse direction, so as to give the angle without the trouble of subtracting the one from the other.

The above apparatus for adjusting the crystal is an improvement suggested by Naumann. In the original instrument the axis \(f_0\) was made to push in or out in a sheath, and had a small brass plate, bent at right angles, inserted in a cleft at \(o\), to which the crystal was attached. The crystal was adjusted, as formerly, by moving the plate, or the axis \(f_0\), and by slight motion of the arm \(ae\), which should be at right angles nearly to \(be\) when used. A considerable improvement is, to have a small mirror fixed on the stand below the crystal, with its face parallel to the axis \(aa\), and inclined at 45° to the window, when the lower line can be dispensed with, and the instrument used for various other purposes of angular measurement. Many alterations have been suggested for the purpose of insuring greater accuracy; but the simple instrument is sufficient for all purposes of determinative mineralogy, and the error from the instrument will in most cases be less than the actual variations in the dimensions of the crystals. Greater simplicity is indeed rather desirable, and the student will often find it sufficient to attach the crystal by a piece of wax to the axis \(a\) directly, and give it the further adjustment by the hand. The only use of the parts from \(b\) to \(q\) is to enable the observer to place the crystal properly; that is, with the edge to be measured parallel to the axis of the instrument, and as nearly as possible coinciding with its centre. This is effected when the reflection of the horizontal bar in the two faces appears parallel to that edge.

**Macles or Twin Crystals.**

When two similar crystals of a mineral species are united with their similar faces and axes parallel, the one forms merely a continuation or enlargement of the other, and every crystal may be regarded as thus built up of a number of smaller crystals. Frequently, however, crystals are united according to precise laws, though all their similar faces and axes are not parallel, and then are named macles or twin crystals. In one class of macles the axes of the two crystals are parallel, and in another they are inclined. The former only occur among hemihedral forms, and the two crystals are then combined in the exact position in which they would be derived from or reproduce the primary holohedric form. The second class, with oblique axes, occur both in holohedric and hemihedral forms, and the two individuals are placed in perfect symmetry to each other, in reference to a particular face of the crystal which forms the plane of union or the equator of the macle. We may also suppose the two crystals originally parallel, and the one turned round the normal of the united faces by 180° (often 90° or 60°), whilst the other is stationary. Or we may suppose a crystal cut into halves in a particular direction, and one-half turned 180° on the other; and hence the name of hemitrope given to them by Hauy. The position of the two individuals in this case corresponds with that of an object and its image in a mirror, whose surface then represents the plane of union.

The manner in which the crystals unite also differs. Some are merely opposed or in simple contact; others are, as it were, grown together, and mutually interpenetrate, occasionally so completely as to appear like one individual. The twin edges and angles in which the two unite are often re-entering; or they may coincide in one plane, when the line of union is either imperceptible, or is only marked by the meeting of two systems of striæ, or other diversity in the physical characters of the two faces.

The formation of twin crystals may be again repeated, forming groups of three, four, or more. When the faces of union are parallel to each other, the crystals form rows of indeterminate extent; where they are not parallel, they may return into each other in circles, or form bouquet-like or other groups. Where crystals are merely in juxtaposition, they are sometimes much shortened in the direction of the twin axis; and where many occur in a series with parallel position, are often compressed into very thin plates, frequently not thicker than paper, giving to the surface of the aggregate a peculiar striated aspect.

Only a few twin crystals in the different systems can be noticed, chiefly as examples of this mode of formation. In duce intersecting macles like the pentagonal dodecahedrons of iron pyrites in fig. 70, and the tetrahedrons of grey-copper or fallore in fig. 71, a similar formation also occurring in the diamond. In macles with inclined axes the two forms almost always unite by a face of the octahedron, and the two individuals are then generally apposed and shortened in the direction of the twin axis by one-half, so that they appear like a crystal that has been divided by a plane parallel to one of its faces, and the two halves turned round on each other by an angle of 180°. In this manner two octahedrons of the spinel, magnetic iron ore, or automolite (fig. 72), are frequently united. The same law prevails in the intersecting cubes of fluor spar, iron pyrites, and galena, represented in fig. 73. In fig. 74 of zinc-blende two rhombic dodecahedrons are united by a face of the octahedron.

In the tetragonal system twin crystals with parallel axes rarely occur, but are seen in copper pyrites, and one or two other minerals. Where the axes are inclined the plane of union is very often one of the faces of the pyramid $P_{\infty}$, or one of those faces that would regularly replace the polar edges of the fundamental form $P$. The crystals of tin ore obey this law, as seen in fig. 75, where the individuals are pyramidal, and in the knee-shaped crystal (fig. 76), where they are more prismatic. Hausmanite appears like fig. 77, in which the fundamental pyramid $P$ prevails, on whose polar edges other crystals are often very symmetrically repeated, a central individual appearing like the support of all the others. Almost identical forms occur in copper pyrites.

In the hexagonal system twin crystals with parallel axes are common, as in calc-spar, chabasite, haematite, and other rhombohedric minerals. In calc-spar they often form very regular crystals, the two individuals uniting by a plane parallel to the base, so as to appear like a single crystal, as in fig. 78, where each end shows the forms $\infty R - \frac{1}{2} R$, but in a complementary position; or in fig. 79 of two scalenohedrons $R^2$ from Derbyshire. The rhombohedric crystals of chabasite often appear intersecting each other, like those of flour spar in fig. 73 above. The purer varieties of quartz or rock-crystal, in consequence of the tetrahexahedral character of its crystallization, often exhibit twins. In these the pyramid $P$ separates into two rhombohedrons $P$ and $r$, which though geometrically similar, are yet physically distinct. In fig. 80 the two individuals are only grown together, but more commonly they penetrate each other in an irregular manner, forming apparently a single crystal. Twins with oblique axes are also common, the plane of union being usually one face of the rhombohedron. Thus in calc-spar two rhombohedrons are often joined by a face of $\frac{1}{2} R$, the two axes forming an angle of $127^\circ 34'$; occasionally a third individual is interposed in a lamellar form, as in fig. 81, when the two outer crystals become parallel. This latter arrangement is very common in the highly cleavable varieties of Iceland spar. When the crystals unite in a face of the rhombohedron $R$, fig. 82, they form an angle of $89^\circ 8'$, differing little from a right angle, by which the occurrence of this law is very easily recognised, especially in prismatic varieties.

In the rhombic system twin crystals with parallel axes are very rare, but those with oblique axes common, the plane of union being one of the faces of the prism $\infty P$. Twins of this kind are very distinctly seen in arragonite, carbonate of lead, marcasite, stephanite, mispickel, and other minerals. In arragonite the crystals partly interpenetrate, partly are in mere juxtaposition, as in fig. 83, where the individuals are formed by the combination $\infty P(m)$, $\infty P(\infty)(h), P(\infty)(s)$, and in figure 84 where several crystals of the same combination form a series with parallel planes of union; the inner members being so shortened that they appear like mere lamellar plates producing striæ on the faces $P_{\infty}$ and $\infty P_{\infty}$ of the macle. In fig. 85 four crystals, each of the combination $\infty P \cdot 2P_{\infty}$, having united in inclined planes, form a circular group, returning into itself. The carbonate of lead often occurs in macles in all respects similar. In staurolite, individuals of the prismatic combination $\infty P \cdot \infty P \cdot OP$, combine either, as in fig. 86, by a face of the brachydome $\frac{1}{2} P_{\infty}$, with their chief axes almost at right angles; or, as in fig. 87, by a face of the brachyhy- Finally, in fig. 88 two harmotome crystals of the most common combination $\infty P \infty$, $\infty P \infty$. $P$, intersect each other so nearly at right angles, that their principal axes seem to coincide, and the brachypinacoid ($q$) of the one crystal (with rhombic striae) is parallel to the macropinacoid ($o$) of the other.

In the monoclinohedric system the most common macles are those in which the principal axes and the chief sections of the two crystals are parallel to each other, and consequently the principal axis is also the twin axis. Usually the two individuals are united by a face parallel to the orthodiagonal chief section, as in figure 89 of gypsum, where two crystals of the combination ($\infty P \infty$), $\infty P$, $-P$, shown in fig. 59, unite so regularly that the faces of the pinacoids ($P$ and $P'$) form only one plane. In a similar manner the augite crystals of the combination $\infty P$, $\infty P \infty$, ($\infty P \infty$), $P$, represented singly in fig. 60, are in fig. 90 united in a macle so very symmetrical and regular that the line of junction cannot be observed on the face of the clinopinacoid. The two hemipyramids $P(s)$ (like $-P(t)$ in the gypsum crystal above) form on one side a re-entering, on the other a salient angle. Hornblende, wolfram, and other minerals exhibit a similar appearance. In other cases the individuals partially penetrate each other, being, as it were, crushed together in the direction of the orthodiagonal. This mode of union is not uncommon in gypsum, and very frequent in orthoclase felspar. Two crystals of the latter, of the combination ($\infty P \infty$), $\infty P$, $0P$, $2P \infty$, as in fig. 61 above, are often pushed sidewise into each other as shown in fig. 91.

In the triclinohedric system some twin formations are of great importance as a means of distinguishing the triclinohedric from the monoclinohedric species of felspar. In one variety the twin axis is the normal to the brachydiagonal chief section. But in the triclinohedric felspars this section is not, as it is in the monoclinohedric species, perpendicular to the basis, and consequently the two bases form on one side a re-entering, on the other a salient angle; whereas in the monoclinohedric felspars (where the brachydiagonal chief section corresponds to the clinodiagonal), no twin crystals can be produced in conformity to this law, and the two bases fall in one plane. The albite and oligoclase very often exhibit such twins, as in figure 92, where the very obtuse angles formed by the faces of $0P$, or $P$ and $P'$ (as well as those of $P' \infty$, or $x$ and $x'$) are a very characteristic appearance, marking out this mineral at once as a triclinohedric species. Usually the twin formation is repeated, three or more crystals being combined, when those in the centre are reduced to mere plates. When very numerous, the surfaces $P$ and $x$ are covered with fine striæ, often only perceptible with a microscope. A second law observed in triclinohedric felspars, particularly the albite and labradorite, is that the twin axis corresponds with that normal of the brachydiagonal, which is situated in the plane of the base. In periclase, a variety of albite, these twins appear as in fig. 93, where the two crystals are united by a face of the basal pinacoid $P$, whilst the faces of the two brachypinacoids ($M$ and $M'$) form edges with very obtuse angles (173° 22'), re-entering on the one side and salient on the other. These edges, or the line of junction between $M$ and $M'$, are also parallel to the edges formed by these faces and the base, or those between $M$ and $P$. In this case also the macles are occasionally several times repeated when the faces appear covered with fine striæ.

Irregular Aggregation of Crystals.

Besides the regular unions now described crystals are often aggregated in peculiar ways, to which no fixed law can be assigned. Thus some crystals, apparently simple, are composed of concentric crusts or shells, which may be removed one after the other, always leaving a smaller crystal like a kernel, with smooth distinct faces. Some specimens of quartz from Beeralston in Devonshire consist apparently of hollow hexagonal pyramids placed one within another. Other minerals, as fluor spar, apatite, heavy spar, and calc-spar, exhibited a similar structure by bands of different colours.

Many large crystals, again, appear like an aggregate of numerous small crystals, partly of the same, partly of different forms. Thus some octahedrons of fluor spar from Schlaggenwald are made up of small dark violet-blue cubes, whose projecting angles give a drusy character to the faces of the larger form. Such polysynthetic crystals, as they may be called, are very common in calc-spar.

A similar, but still more remarkable formation, is where two crystals of distinct species are conjoined. Such unions of cyanite and staurolite have been long well known, and the graphic-granite exhibits a similar union between large felspar crystals and many smaller ones of mica and quartz.

Forms of Crystalline Aggregates.—Crystals have often been produced under conditions preventing the free development of their forms. They then compose crystalline aggregates, of which the following may be distinguished:

- **Granular**, formed of grains, generally angular, but rarely rounded or flattened. - **Lamellar** consist of broad plates, which are **tabular** when of uniform thickness, **lenticular** when becoming thinner on the edges, **wedge-shaped** when sharpened towards one edge, and **scaly** when the plates are very small. - **Columnar**, in which the individuals are drawn out in one direction more than in the others; **bacillary** or rod-like, in which the columns are of uniform thickness; **acicular** or needle-shaped, in which they are pointed; and **fibrous**, in which they are very fine. In the broad-columnar the columns are, as it were, compressed, or broader in one direction than the other. The distinctions of large, coarse, small, or fine-granular; thick or thin scaly; straight, curved, or twisted-columnar; parallel, diverging, or confused-fibrous; and such like, are easily understood.

Aggregates which have been able to crystallize, at least, with a certain degree of freedom, have been distinguished by Mohs into crystal groups and druses; the former including all unions of several imbedded crystals; the latter those of crystals that have grown together on a common support. In the groups crystals with their faces otherwise perfect are conjoined in various ways. Sometimes they radiate, as it were, from a common centre, and produce spheroidal, ellipsoidal, or other forms, frequent in gypsum, iron pyrites, and other minerals imbedded in clay. Where many such masses are united, they are named botryoidal when like bunches of grapes, mammellated where the spheres are larger and less distinct, and reniform or kidney-shaped where the masses are still larger. Some groups are partially attached by a small point; but the mass is generally free.

Crystals are often grouped in rows or in one direction, forming, when they are very small, capillary or hair-like, and filiform, thread, or wire-like forms, which are common among native metals, as gold, silver, copper, and bismuth, in silver glance and a few other minerals. Sometimes the masses are dentiform, consisting of portions resembling teeth; as is very common in silver. Often these groups expand in several directions, and produce arborescent, dendritic, foliated, feathered, or other forms, very common in copper. In these groups, however, a certain dependence on the crystallographic character of the species may be observed. The lamellar minerals often form fan-shaped, wheel-like, almond-shaped, comb-like, or other groups. The fibrous types, again, are disposed in parallel or diverging bundles, or in radiating, stellar, and other masses. Coralloidal (like coral), fruticose (like cauliflower), and other forms, have also been observed.

In druses, many crystals rise side by side from a common support; sometimes only the granular mass composed of their united bases, at other times some distinct body. The form of a druse is determined by that of the surface on which it grows, and consequently is often very irregular or wholly accidental. Where completely inclosed they have been named drusy cavities, and when of a spheroidal form, geodes. A drusy crust, again, consists of a thin layer of small crystals investing the surface of a large crystal or of some other body.

The minute or cryptocrystalline minerals form similar aggregates. In the globular or the oolitic the minute crystals often appear to radiate from a centre, or form concentric crusts. Somewhat similar are the stalactites and stalagmites, in which the mineral, especially rock-salt, limestone, chalcedony, opal, limonite, has been deposited from a fluid dropping slowly from some overhanging body. In this case the principal axis of the figure, generally a hollow tube, is vertical, whilst the individual parts are arranged at right angles to this direction. In other cases the mineral has apparently been deposited from a fluid mass moving slowly in a particular direction, which may be regarded as the chief axis of the figure, whilst the axes of the individual crystals may assume a different position.

By far the largest masses of the mineral kingdom have, however, been produced under conditions in which a free development of their forms was excluded. This has been the case with the greater portion of the minerals composing rocks or filling veins and dykes. The structure of these masses on the large scale belongs to geology, but some varieties of the texture visible even in hand specimens may be noticed. The individual grains or masses have seldom any regular form, but appear round, long, or flat, according to circumstances, and as each has been more or less checked in the process of formation. Even then, however, a certain regularity in the position of the parts is often observable, as in granite, in which the cleavage planes, and consequently the axes of the felspar crystals, are parallel. Where these grains are all pretty similar in size and shape, the rock is named massive when they are small, or granular when they are larger and more distinct. Sometimes the rock becomes slaty, dividing into thin plates; or concretionary, forming roundish masses; at other times the interposition of some foreign substance (gas or vapour) has rendered it porous, cellular or vesicular, giving rise to drusy cavities. These cavities are often empty, but have occasionally been filled by other minerals, when the rock is named amygdaloidal, from the almond-like shape of the inclosed masses.

Many of the above external forms appear also in the amorphous solid minerals, in which no trace of individual parts, and consequently of internal structure, is observable. They are not unfrequently disposed in parallel or concentric layers, of uniform or distinct colours; and may assume spherical, cylindrical, stalactitic, and other appearances.

**Pseudomorphism.**—When the substance of one mineral assumes the external form of some other mineral it is named a pseudomorph. In some named incrusting pseudomorphs the original crystal is covered by a rough or drusy surface of the second mineral, frequently not thicker than paper. Occasionally the first crystal has been removed, and nothing but the shell remains; or the cavity has been filled by a distinct mineral species, or a crystalloid, as it may be named, forming an exact representation of the original, but of a different substance.

More commonly the new mineral substance has gradually expelled the old, and replacing it, as it were, atom by atom, has assumed its exact form. In other cases not the whole substance of the original crystal, but only one or more of its elements, has been changed, or the whole matter has remained, but in a new condition. Thus arragonite crystals have been converted into calc-spar, the chemical composition of both being identical; or gaylussite has been changed into calc-spar, andalusite into cyanite, by the loss of certain elements. On the other hand, anhydrite becomes gypsum, red-copper ore malachite, by addition of new matter. Or the elements are partially changed, as felspar into kaolin, quartz or pearl spar into talc, iron pyrites or iron glance into brown-iron ore, azurite into malachite, augite into green earth. The true nature of such bodies is shown by the internal structure, having no relation to the external form or apparent system of crystallization.

The process of petrification of organic bodies is in reality a species of pseudomorphic formation, and has been produced in all the above modes. External and internal casts of organic bodies are not uncommon. In other cases the original substance has been replaced by some mineral which has preserved not merely the external form, but even the minutest detail of internal structure; so that the different kinds of wood have been distinguished in their silicified trunks. The most common petrifying substances are silica and carbonate of lime. In encrinites, echinites, belem- nites, and other fossils; the crystals of calc-spar often occur in very regular positions. In some varieties of petrified wood both the ligneous structure and the cleavage of the calc-spar are observable.

Different from the above are mineralized bodies, in which the original structure is still retained, but their chemical nature partially changed. In these a complete series may be often traced, as from wood or peat, through the varieties of brown coal, common coal, anthracite, and graphite, perhaps even to the diamond.

**Chap. II.—Physical Properties of Minerals.**

The physical characters of minerals comprehend,—1st. Those properties derived from the nature of the substance itself, as coherence, mode of fracture, elasticity, and density or specific gravity. 2d. Those phenomena called forth in minerals by the influence of some external power or agent, as their optical, electric, or thermal relations; and, 3d. Other characters depending on the personal sensation of the observer, on his taste, smell, and touch. All these properties furnish useful characters in distinguishing and describing mineral species.

**Cleavage and Fracture.**

In many species there are certain planes at right angles to which cohesion seems to be at a minimum, so that the mineral separates along or parallel to these planes far more readily than in any other direction. This property is named cleavage, and these planes cleavage-planes. They have a strictly definite position, and do not show any transition or gradual passage into the greater coherence in other directions. The number of these parallel cleavage-planes is altogether indefinite; so that the only limit that can be assigned to the divisibility of some minerals, as gypsum and mica, arises from the coarseness of our instruments.

These minima of coherence or cleavage-planes are always parallel to some face of the crystal, and similar equal minima occur parallel to every other face of the same form. Hence they are always equal in number to the faces of the form, and the figures produced by cleavage agree in every point with true crystals, except that they are artificial. They are thus most simply and conveniently described by the same terms and signs as the faces of crystals. Some minerals cleave in several directions parallel to the faces of different forms, but the cleavage is generally more easily obtained and more perfect in one direction than in the others. This complex cleavage is well seen in calc-spar, and fluor spar, and very remarkably in zinc-blende, where it takes place in no less than six directions. As in each of these the division may be indefinitely continued, it is clear that no lamellar structure in any proper sense can be assigned to the mineral. All that can be affirmed is, that contiguous atoms have less coherence in the normal of these planes than in other directions. When the cleavage takes place in three directions, it of course produces a perfect crystal form, from which the system of crystallization and angular dimensions of the species may be discovered, and is thus often of very great importance.

The common cleavage in the different systems is as follows, those of most frequent occurrence being put in italics:

—(1.) In the tesserall, Octahedric, O, along the faces of the octahedron; Hexahedric, \( \infty O \infty \), along those of the cube; and Dodecahedric, \( \infty O \infty \). (2.) In the tetragonal system, Pyramidal, P or \( 2P\infty \); Prismatic, \( \infty P \) or \( \infty P\infty \); or Basal, OP. (3.) In the hexagonal system with holohedral forms, Pyramidal, P or \( P^2 \); Prismatic, \( \infty P \) or \( \infty P^2 \); or Basal, OP; with rhombohedral forms, Rhombohedric, R; Prismatic, \( \infty R \); or Basal, OR. (4.) In the rhombic system, Pyramidal, P; Prismatic, \( \infty P \); Makro or Brachydomatic, \( P\infty \) or \( P^2 \); Basal, OP; Macrodiaogonal, \( \infty P\infty \); or Brachydiaogonal, \( \infty P^2 \). (5.) In the monoclinobedric system, Hemipyramidal, P or \( -P \); Prismatic, \( \infty P \); Clinodomatic, \( P\infty \); Hemidomatic, \( P\infty \) or \( -P\infty \); Basal, OP; Orthodiagonal, \( \infty P\infty \); or Clinodiagonal, \( \infty P\infty \). (6.) In the triclinobedric system, Hemiprismatic, \( \infty P' \) or \( \infty P \); Hemidomatic either along the macrodome or brachy dome; Basal, OP; Macrodiaogonal, \( \infty P\infty \); or Brachydiaogonal, \( \infty P^2 \).

In some minerals the cleavage is readily procured; in others only with extreme difficulty. The planes produced also vary much in their degree of perfection, being highly perfect in some, as mica and gypsum; imperfect in others, as garnet and quartz. In a very few crystalline minerals cleavage-planes can hardly be said to exist. Cleavage must be carefully distinguished from the planes of union in twin crystals, and the division-planes in the laminar minerals.

Fracture surfaces are formed when a mineral breaks in a direction different from the cleavage-planes. They are consequently most readily observed when the cleavage is least perfect. The form of the fracture is named conchoidal when composed of concave and convex surfaces like shells, even when nearly free from inequalities. The character of the surface is smooth; or splintery when covered by small wedge-shaped splinters adhering by the thicker end; or hackly when covered by small slightly-bent inequalities, as in iron and other malleable bodies; or earthy when it shows only fine dust.

**Hardness and Tenacity.**

The hardness of minerals, or their power of resisting any attempt to separate their parts, is also an important character. As it differs considerably in the same species, according to the direction and the surface on which the trial is made, its accurate determination is difficult, and the utmost that can usually be obtained is a mere approximation found by comparing different minerals one with another. For this purpose Mohs has given the following scale:

1. Talc, of a white or greenish colour. 2. Rock-salt, a pure cleavable variety, or semitransparent uncrystallized gypsum, the transparent and crystallized varieties being generally too soft. 3. Calcareous spar, a cleavable variety. 4. Fluor spar, in which the cleavage is distinct. 5. Apatite, the asparagus-stone, or phosphate of lime, from Salzburg. 6. Adularia felspar, any cleavable variety. 7. Rock-crystal, a transparent variety. 8. Prismatic topaz, any simple variety. 9. Corundum from India, which affords smooth cleavage surfaces. 10. The Diamond.

Two other degrees are obtained by interposing foliated mica between 2 and 3, and scapolite, a crystalline variety, between 5 and 6. The former is numbered 2½, the latter 5½.

To ascertain the hardness of a mineral, first try which of the members of the scale is scratched by it, and in order to save the specimens, begin with the highest numbers, and proceed downwards, until reaching one which is scratched. Then take a fine hard file, and draw along its surface, with the least possible force, the specimen to be examined, and also that mineral in the scale whose hardness is immediately above the one which has been scratched. From the resistance they offer to the file, from the noise occasioned by their passing along it, and from the quantity of powder left on its surface, their relative hardness is deduced. When, after repeated trials, we are satisfied to which member of the scale of hardness the mineral is most nearly allied, we say its hardness (suppose it to be felspar) is equal to 6, and write after it $H = 6$. If the mineral do not exactly correspond with any degree of the scale, but is found to be between two of them, it is marked by the lower with a decimal figure added. Thus, if more than 6 but less than 7, it is expressed $H = 6.5$. In these experiments we must be careful to employ specimens which nearly agree in form and size, and also as much as possible in the shape of their angles.

Where the scale of hardness is wanting, or for a first rough determination, the following experiments may serve:

Every mineral that is scratched by the finger-nail has $H = 2.5$ or less.

Minerals that scratch copper have $H = 3$ or more.

Polished white iron has $H = 4.5$.

Window-glass has $H = 5$ to $5.5$.

Steel point or file has $H = 6$ to $7$.

Hence every mineral that will cut or scratch with a good penknife has $H$ less than 6.

Flint has $H = 7$ and only about a dozen minerals, including the precious stones or gems, are harder.

Closely allied to hardness is the tenacity of minerals, of which the following varieties have been distinguished:—A mineral is said to be brittle when, as in quartz, on attempting to cut it with a knife, it emits a grating noise, and the particles fly away in the form of dust. It is sectile or mild when, as in galena and some varieties of mica, on cutting, the particles lose their connection in a considerable degree; but this takes place without noise, and they do not fly off, but remain on the knife. And a mineral is said to be soft or ductile when, like native gold or lead, it can be cut into slices with a knife, extended under the hammer, and drawn into wire. From tenacity it is usual to distinguish fragility, or the resistance which minerals oppose when we attempt to break them into pieces or fragments. This property must not be confounded with hardness. Quartz is hard, and hornblende comparatively soft; yet the latter is more difficultly frangible than the former. Flexibility, again expresses the property possessed by some minerals of bending without breaking. They are elastic, like mica, if, when bent, they spring back again into their former direction; or merely flexible, when they can be bent in different directions without breaking, but remain in their new position, as gypsum, talc, asbestos, and all malleable minerals.

Specific Gravity.

The density or the relative weight of a mineral, compared with an equal volume of pure distilled water, is named its specific gravity. This is a most important character for distinguishing minerals, as it varies considerably in different species, and can be readily ascertained with much accuracy, and in many cases without at all injuring the specimen. The whole process consists in weighing the body, first in air, and then immersed in water, the difference in the weight being that of an equal bulk of the latter fluid. Hence, assuming, as is commonly done, the specific gravity of pure distilled water to be equal to 1 or unity, the specific gravity ($G$) of the other body is equal to its weight in air ($w$), divided by the loss or difference ($d$) of weight in water (or $G = \frac{w}{d}$).

A simple and portable instrument for finding the specific gravity is the arcometer of Nicholson, fig. 94. A delicate hydrostatic balance gives the gravity with far more accuracy; and even a good common balance is often preferable. The mineral may be suspended from one arm or scale by a fine silk thread or hair, and its weight ascertained, first in the air, and then in water.

There are a few precautions necessary to insure accuracy. Thus, a pure specimen must be selected which is not intermixed with other substances, and when weighed in air it should be quite dry. It must also be free from cavities, and care must be taken that when weighed in water no globules of air adhere to its surface, which render it lighter. If the body imbibes moisture, it should be allowed to remain till fully saturated before determining its weight when immersed, and it is sometimes even necessary to boil the specimen in order to expel the air from its pores. Small crystals or fragments, whose freedom from mixture can be seen, are best adapted for this purpose. The specimen experimented on should not be too heavy; thirty grains being enough where the gravity is low, and even less where it is high. It is also of importance to repeat the trial, if possible with different specimens, which will show whether any cause of error exists, and to take the mean of the whole. A correction should be made for the variation of the temperature of the water from 60° Fahr., which is that usually chosen as the standard in mineralogical works. Where the difference, however, does not exceed ten or fifteen degrees this correction may be neglected, as it only affects the third or second decimal figure of the result.

Optical Properties of Minerals.

There are few more interesting departments of science than the relations of mineral bodies to light, and the modifications which it undergoes either when passing through them or when reflected from their surface. In this place, however, we can only notice these phenomena so far as they point out distinctions in the internal constitution of minerals, or furnish characters for distinguishing one species from another.

Minerals, and even different specimens of the same species, vary much in pellucidity or in the quantity of light which can pass through them. Some transmit so much light, that small objects can be clearly seen, or letters read when placed behind them, and are named transparent. They are semitransparent when the object is only seen dimly, as through a cloud; and translucent when the light that passes through it is so obscured that the objects can be no longer discerned. Some minerals are only thus translucent on the thinnest edges, and in others even these transmit no light, and the body is named opaque or untransparent. These degrees pass gradually into each other, and cannot be separated by any precise line; and this is also the case in nature, where some minerals pass through the whole scale, as quartz, from the fine transparent rock-crystal to opaque dark-black varieties. Such minerals may be described generally as pellucid. This change often arises from some mixture in their composition, especially of metallic substances. Perfect opacity is chiefly found in the metals or their compounds with sulphur, though even these seem to transmit light when reduced to laminae of sufficient thinness.

Double Refraction.—When a ray of light passes obliquely from one medium into another of different density, it is bent or refracted from its former course. The line which it then follows forms an angle with the perpendicular, which in each body bears a certain proportion to that at which the ray fell upon it, or, as definitely stated, the sine of the angle of refraction has a fixed ratio to the sine of the angle of incidence, this ratio being named the index of refraction. This simple refraction is common to all trans- parent bodies, whether crystalline, amorphous, or fluid; but some crystals produce a still more remarkable result. The ray of light which enters them as one is divided into two rays, each following different angles, or is doubly refracted. In minerals of the tesselar system this property does not exist, but it has been always observed in minerals belonging to the other systems, though in many only after they have been cut in a particular manner, or have been otherwise properly prepared. It is most distinctly seen in crystals of calc-spar, especially in the beautiful transparent variety from Iceland, in which it was first observed and described by Erasmus Bartholin in a work published at Copenhagen in 1669.

The subjoined figure will illustrate this singular property. It represents a rhomb of Iceland spar, on the surface of which a ray of light \( Rr \) falls. As seen in the figure, this ray divides into two, one of which \( roo' \) follows the ordinary law of refraction, or the sines of the angles of incidence and refraction maintain a constant ratio. This is named the ordinary ray \( O \). The other, hence named the extraordinary ray \( E \), does not obey the usual law of the sines, and has no general index of refraction. In the plane perpendicular to the axis it is most widely separated from the ordinary ray, but in others oblique to it approaches nearer to \( O \), and in one at right angles coincides, or there is no double refraction. This plane, or rather direction, in which there is no double refraction, is named the optical axis of the crystal, or the axis of double refraction. Now, in certain minerals it is found that there is only one plane with this property, whereas in others there are two such planes, and they have in consequence been divided into monoxial and biaxial. To the former (monoxial) belong all crystals of the tetragonal and hexagonal systems; to the latter (biaxial) all those of the three other systems. In the former the optic axis coincides with, or is parallel to, the crystallographic chief axis. In some crystals the index of refraction for the extraordinary ray \( E \) is greater than for the ordinary ray \( O \); and in others it is smaller. The former are said to have positive (or attractive), the latter negative (or repulsive) double refraction. Quartz is an example of the former, the index of refraction, according to Malus, being for \( O = 1:6484 \), for \( E = 1:5582 \); and calc-spar of the latter, the index of \( O \) being \( = 1:6543 \), of \( E = 1:4833 \). The index of \( E \) is in both cases taken as its maximum.

It should be observed that the optic axes are not single lines, but directions parallel to a line, or innumerable parallel lines, passing through every atom of the crystal. It is also important to remark that this property divides the systems of crystallization into three precise groups,—the tesselar, with single refraction; the tetragonal and hexagonal, with double refraction, and monoxial; the other three systems also double, but biaxial. It is therefore of use to determine the system to which a mineral belongs, but is not of great value as a character for distinguishing species.

**Polarization of Light.—** Intimately connected with this property is that of the polarization of light, which being more easily and precisely observable than double refraction, is in many cases of higher value as a mineralogical character. By this term is meant a peculiar modification which a ray of light undergoes, in consequence of which its capability of being transmitted or reflected towards particular sides is either wholly or partially destroyed. Thus, if from a transparent prism of tourmaline two thin plates are cut parallel to its axis, they will transmit light, as well as the prism itself, when they are placed above each other with the chief axis of both in the same direction. But when the one slip of tourmaline is turned at right angles to the other, either no light at all or very little is transmitted, and the plates consequently appear black. Hence, in passing through the first slip the rays of light have acquired a peculiar property, which renders them incapable of being transmitted through the second, except in a parallel position, and they are then said to be polarized. The same property is acquired by a ray of light when reflected, at an angle of \( 35^\circ \) (or angle of incidence \( 54^\circ \)), from a plate of glass, one side of which is blackened, or from some other non-metallic body. When such a ray falls on a second similar mirror at an equal angle, but so that the plane of reflection in the second is at right angles to that in the first, it is no longer reflected, but wholly absorbed. When, on the other hand, the planes of reflection are parallel, the ray is wholly and at any intermediate angle partially reflected. A ray of light polarized by reflection is also incapable of transmission through a tourmaline slip in one position, which, however, is at right angles to that in which a ray polarized by passing through another slip is not transmitted.

In order to observe the polarization of light, a very simple instrument will be found useful (fig. 96). At one end of a horizontal board \( B \) a black mirror \( a \) is fixed. In the middle is a pillar to which a tube \( cd \) is fastened, with its axis directed to the mirror at an angle of \( 35^\circ \).

On the lower end is a cover \( e \), with a small hole in the centre, and at the upper end another cover with a small black mirror \( m \) attached to it by two arms, as in the figure, and also at an angle of \( 35^\circ \). With this instrument the mirror \( m \) can be so placed in relation to \( a \) that the planes of reflection shall have any desirable inclination to exhibit the simple polarization of light.

This instrument furnishes a simple test whether minerals that cleave readily into thin lamellae are optically monoxial or biaxial. Place the two mirrors with their polarization-planes at right angles, and fix a plate of the mineral with a little wax over the hole \( c \), and then observe what takes place in the second mirror during the time that the cover \( e \) is turned round. If the mineral belongs to the biaxial system, the light from the first mirror \( a \), in passing through it, is doubly refracted and has its polarization changed, and consequently can be again reflected from the second mirror \( m \), and in each revolution of \( e \) will show four maxima and four minima of intensity. If, on the contrary, the mineral is monoxial, the ray will pass through the lamina unaltered, and will not be reflected from the second mirror in any position of \( e \).

Another beautiful phenomenon of polarized light, in like manner connected with the crystalline structure of minerals, is the coloured rings which laminae of the doubly-refracting species, when of a proper thickness, exhibit in certain positions. These rings are easily seen in the above apparatus by interposing a thin plate of gypsum or mica between the two mirrors. When the interposed plate belongs to a monoxial mineral, there is seen in the second mirror a system of circular concentric coloured rings in... Mineralogy.

If the mineral is biaxial, one or two systems of elliptical coloured rings appear, each intersected by a black stripe (fig. 98). In certain cases this stripe is curved, or the two systems of rings unite in a lemniscoidal form (fig. 99). When the planes of polarization are parallel, the black cross and stripe appear white (fig. 100), showing that in this direction the crystals act like singly-refracting minerals. Quartz, again, in close relation to its system of crystallization, exhibits a circular polarization of splendid prismatic colours, which on turning the plate change in each point in the order of the spectrum, from red to yellow, green, and blue. In order to produce these changes, however, in some specimens the plate must be turned to the right, in others to the left, showing a difference in the crystalline structure.

Pleochroism.—Closely connected with double refraction is that property of transparent minerals named pleochroism (many-coloured), in consequence of which they exhibit distinct colours when viewed by transmitted light in different directions. Crystals of the tesserac system do not show this property; whilst in those of the other systems it appears in more or less perfection; and in the tetragonal and hexagonal minerals as dichroism (two colours), in the rhomboic and clinohedric systems as trichroism (three colours). In most cases these changes of colour are not very decided, and appear rather as different tints or shades than as distinct colours. The most remarkable of dichromatic minerals are the magnesian mica from Vesuvius, the tourmaline and epidolite; of trichromatic, the iolite, the andalusite from Brazil, the diaspore from Schenmizt, and the axinite.

Some crystalline minerals exhibit a very lively play or change of colours from reflected light in certain directions. It is well seen in many various hues on the cleavage-planes of Labrador felspar, and seems produced by a multitude of very thin quadrangular pores, interposed in the mineral-like minute parallel laminae. On the cleavage-planes of the hypersthene it appears copper-red, and is occasioned by numerous small brown or black laminae of some foreign substance interposed in a parallel position between the planes of the hypersthene. The chatoyant, or changing colours of the sun-stone, arise from scales of iron glance similarly interposed. The play of colour in the noble opal seems to be produced very nearly in the same manner with that in the labradorite. A similar opalescence is seen in certain minerals when cut in particular forms. In the sapphire, cut hemispherically over the chief axis, it appears like a star with six rays; in certain varieties of chrysoberl and adularia it has a bluish tint; and is also very remarkable in the cat's-eye variety of quartz. Iridescence often arises from very fine fissures, producing semicircular arches of prismatic tints, which, like the colours of thin plates in general, are referred to the interference of light.

Lustre and Colour.

Though these properties admit of no precise or mathematical determination, they are of considerable value in mineralogy. One highly important distinction founded on them is that of minerals of metallic and non-metallic aspect or character. This distinction can hardly be described in words, and the student will best learn to distinguish metallic colours and lustre from non-metallic by observing them in nature. Transparency and opacity nearly coincide with this division, the metallic minerals being almost constantly opaque; the non-metallic more or less transparent. Minerals which are perfectly opaque, and show metallic colour and lustre, are named metallic; those with only two of these three properties, semi-metallic or metalloid; and those with the opposite properties non-metallic.

Lustre has reference to the intensity and quality of the reflected light, considered as distinct from colour. Several degrees in intensity have been named. (1.) Splendid, when a mineral reflects light so perfectly as to be visible at a great distance, and lively, well-defined images are formed in its faces, as galena, rock-crystal, or calc-spar. (2.) Shining, when the reflected light is weak, and only forms indistinct and cloudy images, as heavy spar. (3.) Glistening, when the reflected light is so feeble as not to be observable at a greater distance than arm's length, and the surface can no longer form an image. (4.) Glittering, when the mineral held near the eye in full clear daylight presents only a number of small shining points, as red haematite and granular limestone. When, as in chalk, the lustre is so feeble as to be indiscernible, it is said to be dull.

In regard to the kind or quality of the lustre, the following varieties are distinguished:—(1.) The metallic, seen in much perfection in native metals and their compounds with sulphur, and imperfectly in glance coal. (2.) Adamantine, found in beautiful perfection in the diamond, and in some varieties of blende and carbonate of lead. (3.) Vitreous or glassy, seen in rock-crystal or common glass, or inclining to adamantine in flint-glass. (4.) Resinous, when the body appears as if smeared with oil, as in pitchstone and garnet. (5.) Pearly, like mother-of-pearl, seen in stilbite, gypsum, mica. (6.) Silky, the glimmering lustre seen on fine fibrous aggregates like amianthus.

Colour.—This property is not in all cases of equal value as a character. Thus some minerals are naturally coloured, showing in all modes of their occurrence one determinate colour, which is therefore essential, and forms a characteristic of the species. This class includes the metals, pyrites, blends, with many metallic oxides and salts. A second class of minerals are colourless, their purest forms being white, or clear like water, as ice, calc-spar, quartz, adularia, and many silicates. But these minerals are occasionally coloured,—that is, accidentally tinged, sometimes from the chemical or mechanical admixture of some colouring substance, as a metallic oxide, carbon, or particles of coloured minerals; at other times from the substitution of a coloured for an uncoloured isomorphous element. The colours of these minerals therefore vary indefinitely, and can never characterize the species, but only its varieties. Thus, quartz, calc-spar, fluor spar, gypsum, and felspar are often coloured accidentally by pigments mechanically mixed; and hornblende, augite, garnet, and other colourless silicates acquire green, brown, red, or black tints from the introduction of the isomorphous colouring elements.

Werner, who bestowed much attention on this portion of mineralogy, distinguished eight principal colours,—white, gray, black, blue, green, yellow, red, and brown,—each with several varieties or shades arising from intermixture with the other colours. He also divided them into metallic and non-metallic as follows:

**METALLIC COLOURS.**

1. **White.**—(1.) Silver-white, as in leucosite and native silver. (2.) Tin-white; native antimony.

2. **Gray.**—(1.) Lead-gray; galena or lead glance. (2.) Steel-gray; native platinum.

3. **Black.**—(1.) Iron-black; magnetite.

4. **Yellow.**—(1.) Brass-yellow; chalcopyrite. (2.) Bronze-yellow; iron pyrites. (3.) Gold yellow; native gold.

5. **Red.**—(1.) Copper-red; native copper and nickelline.

**NON-METALLIC COLOURS.**

1. **White.**—(1.) Snow-white; new fallen snow, Carrara marble, and common quartz. (2.) Reddish-white; heavy spar. (3.) Yellowish-white; chalk. (4.) Greyish-white; quartz. (5.) Greenish-white; amiantus.

2. **Gray.**—(1.) Blush-gray; limestone. (2.) Pearl-gray; porcelain jasper, and rarely quartz. (3.) Smokey-gray or brownish-gray; dense smoke, dark varieties of flint. (4.) Greenish-gray; clay slate and wheal slate. (5.) Yellowish-gray; chaledony. (6.) Ash-gray; wood-ashes, zoisite, zircon, and slate-clay.

3. **Black.**—(1.) Grayish-black; basalt, Lydian stone, and jacinthite. (2.) Velvet-black; obsidian and schorl. (3.) Pitch-black or brownish-black; cobalt ochre, bituminous coal, and some varieties of mica. (4.) Greenish-black or raven-black; hornblende. (5.) Blush-black; fluor spar.

4. **Blue.**—(1.) Blackish-blue; dark varieties of azurite. (2.) Azure-blue; bright varieties of azurite and Lapis lazuli. (3.) Violet-blue; amethyst and fluor spar. (4.) Lavender-blue; lithomarge and porcelain jasper. (5.) Plum-blue; spinel and fluor spar. (6.) Berlin-blue; sapphire, rock-salt, cyanite. (7.) Smalt-blue; pale-coloured smalt, gypseum. (8.) Duck-blue; tale and corundum. (9.) Indigo-blue; early-blue iron or vivianite. (10.) Sky-blue; hirocomite, some varieties of fluorspar and of blue spar.

5. **Green.**—(1.) Verdigris-green; amazon stone and hirocomite. (2.) Celandine-green; emerald, aquamarine, and Brazilian beryl. (3.) Mountain-green; beryl, aquamarine topaz. (4.) Leek-green; common actinolite and prase. (5.) Emerald-green; emerald, and some varieties of green micaschiste. (6.) Apple-green; chrysoberyl. (7.) Grass-green; uranite, amaranite. (8.) Blackish-green; augite and precious serpentine. (9.) Platschite-green; chrysolite and epidote. (10.) Asparagus-green; the apatite or asparagus-stone from Spain and Salzburg. (11.) Olive-green; garnet, pitch-stone, and olivine. (12.) Oil-green; olive oil, beryl, beryl. (13.) Stakin-green; uranite, and some varieties of pyromorphite.

6. **Yellow.**—(1.) Sulphur-yellow; native sulphur. (2.) Straw-yellow; pyrite and karpholite. (3.) Wax-yellow; opal and wilfellite. (4.) Honey-yellow; dark honey, fluor spar, and beryl. (5.) Lemon-yellow; rind of ripe lemon, orpiment. (6.) Ochre-yellow; yellow-earth and jasper. (7.) Wine-yellow; Saxon and Brazilian topaz and fluor spar. (8.) Cream-yellow or Isabella-yellow; bolo from Strigian, and compact limestone. (9.) Orange-yellow; rind of the ripe orange, uran-ochre, and some varieties of wilfellite.

7. **Red.**—(1.) Aurora, or morning-red; zeolite. (2.) Hyacinth-red; hyacinth or zircon, and garnet. (3.) Tile-red; fresh-burned bricks, porcelain-jasper, and hematite. (4.) Scarlet-red; light-red cinnamon. (5.) Blood-red; blood, pyrite. (6.) Flesh-red; felspar and barytes. (7.) Carmine-red; carmine spinel, particularly in this spinelites. (8.) Cochineal-red; cinnamon and certain garnets. (9.) Crimson-red; oriental ruby and erythrine. (10.) Columbine-red; precious garnet. (11.) Rose-red; diadohite and rose-quartz. (12.) Peach-blossom red; blossoms of the peach, red cobalt-ochre. (13.) Cherry-red; anisel, kermes, and precious garnet. (14.) Brownish-red; reddle and columnar-clay ironstone.

8. **Brown.**—(1.) Reddish-brown; brown blends from the Hartz, and zircon. (2.) Clove-brown; the clove, rock-crystal, and axinite. (3.) Hair-brown; wood-opal and limonite. (4.) Broccoli-brown; Minas-zircon. (5.) Chestnut-brown; Egyptian jasper. (6.) Yellowish-brown; iron-dirt and jasper. (7.) Pinchbeck-brown; tarnished plumbecite, mica. (8.) Wood-brown; mountain wood and old rotten wood. (9.) Liver-brown; boiled liver, common jasper. (10.) Blackish-brown; mineral pitch and brown coal.

The accidentally coloured minerals sometimes present two or more colours or tints, even on a single crystal; very remarkable examples occurring in fluor spar, apatite, sapphire, amethyst, tourmaline, and cyanite. This is still more common in compound minerals, on which the colours are variously arranged in points, streaks, clouds, veins, stripes, bands, or in brecciated and ruin-like forms. Some minerals again change their colour from exposure to the light, the air, or damp. Sometimes merely the surface is affected or tarnished, and then appears covered as with a thin film, producing in some minerals, as silver, arsenic, bismuth, only one colour; in others, as copper pyrites, hematite, stibine, and common coal, various or iridescent hues. Occasionally the change pervades the whole mineral, the colour sometimes becoming paler, or disappearing as in chrysoprase and rose-quartz; at other times darker, as in brown spar, siderite, and rhodonite. In a few minerals a complete change of colour takes place, as in the chlorophite of the Western Isles, which, on exposure for a few hours, passes from a transparent yellow-green to black. These mutations seem generally connected with some chemical change. The tarnished colours sometimes only appear on certain faces of a crystal belonging to a peculiar form. Thus a crystal of copper pyrites (like fig. 35) has one face P' free from tarnish; the faces b and c, close to P', are dark blue; the remainder of c, first violet, and then, close to P, gold-yellow. The colour of the powder formed when a mineral is scratched by a hard body is often different from that of the solid mass. This is named the streak, and is very characteristic of many minerals. It also often shows a peculiar lustre where the mineral is soft, as in talc and steatite.

**Phosphorescence, Electricity, Magnetism.**

Phosphorescence is the property possessed by particular minerals of producing light in certain circumstances without combustion or ignition. Thus some minerals appear luminous when taken into the dark after being for a time exposed to the sun's rays, or even to the ordinary daylight. Many diamonds and calcined barites exhibit this property in a remarkable degree; less so, argonite, calc-spar, and chalk; and in a still inferior degree, rock-salt, fibrous gypsum, and fluor spar. Many minerals, including the greater part of those thus rendered phosphorescent by the influence of the sun, also become so through heat. Thus some topazes, diamonds, and varieties of fluor spar become luminous by the heat of the hand; other varieties of fluor spar and the phosphorite require a temperature near that of boiling water; whilst calc-spar and many silicates are only phosphorescent at from 400° to 700° Fahr. Electricity produces it in some minerals, as in green fluor spar and calcined barites. In others it is excited when they are struck, rubbed, split, or broken; as many varieties of zinc-blende and dolomite when scratched with a quill; pieces of quartz when rubbed on each other, and plates of mica when suddenly separated.

Friction, pressure, and heat also excite electricity in minerals. To observe this property delicate electrosopes are required, formed of a light needle, terminating at both ends in small balls, and suspended horizontally on a steel pivot by an agate cup. Such an instrument can be negatively electrified by touching it with a stick of sealing-wax, excited by rubbing, or positively when the wax is only brought so near as to attract the needle. When the instrument is in this state the mineral, if also rendered elec- tric by heat or friction, will attract or repel the needle according as it has acquired electricity of an opposite or similar kind; but if the mineral is not electric, it will attract the needle in both conditions alike. Most precious stones become electrical from friction, and are either positive or negative according as their surface is smooth or rough. Pressure even between the fingers will excite distinct positive electricity in pieces of transparent double-refracting calc-spar. Topaz, arragonite, fluor spar, carbonate of lead, quartz, and other minerals show this property, but in a much smaller degree.

Heat or change of temperature excites electricity in many crystals, as in tourmaline, calamine, topaz, calc-spar, beryl, barytes, fluor spar, diamond, garnet, and others, which are hence said to be thermo- or pyro-electric. Some acquire polar pyro-electricity, or the two electricities appear in opposite parts of the crystal, which are named its electric poles. Each pole is alternately positive and negative,—the one when the mineral is heating, the other when it is cooling. The poles that become positive during an increase of temperature are named analogue; those that become negative in the same condition, antilogue poles, as shown in this table:

| Temperature | Produces | Electricity | |-------------|----------|-------------| | + or rising | in analogue | + or vitreous | | - or falling | poles | - or resinous | | + or rising | in analogue | - or resinous | | - or falling | poles | + or vitreous |

As already noticed, many polar electric minerals are also remarkable for their hemimorphic crystal forms. The number and distribution of the poles likewise vary. In many monoaxial minerals, as tourmaline and calamine, there are only two poles, one at each end of the chief axis; whereas boracite has eight poles corresponding to the angles of the cube. In prehnite and topaz, again, two antilogue poles occur on the obtuse lateral edges of the prism ξP, and one analogue pole corresponding to the monoclinoidal chief section, or in the middle of the diagonal joining the obtuse edges.

Magnetism, or the power to act on the magnetic needle, is very characteristic of the few minerals in which it occurs, chiefly ores of iron or nickel. It is either simple, attracting both poles of the needle; or polar, when one part attracts, and another repels the same pole. Some magnetic iron ores, or natural magnets, possess polar magnetism; whilst the common varieties, meteoric iron, magnetic pyrites, precious garnet, and other minerals, are simply magnetic. Most minerals are only attracted by the magnet, but do not themselves attract iron.

Smell, taste, and touch furnish a few characters of minerals. Most have no smell, but some give out a peculiar odour when rubbed: as quartz an empyreumatic odour, or smell of burning; fluor spar of chlorine; clay of clay; some limestones and marls of bitumen, or a fecid odour. Aluminous minerals acquire a smell when breathed on. Other odours caused by heat, and often highly characteristic, are noticed under tests by the blow-pipe.

Taste is produced by all the salts soluble in water. Some are saline, like common salt; sweetish astringent, like alum; astringent, like blue vitriol; bitter, like epsom salt; cooling, like saltpetre; pungent, like sal-ammoniac; alkaline, like soda; acid or sour, like sassoline, &c.

Touch.—Some minerals are distinguished by a greasy feeling, like tale; others feel meagre, like clay; others cold. The last character readily distinguishes true gems from their imitations in glass.

**CHAP. III.—CHEMICAL PROPERTIES OF MINERALS.**

The consideration of the chemical nature of minerals,—that is, of the elements that enter into their composition,—of the manner in which these elements combine, and the variations in proportion which they may undergo without destroying the identity of the species, forms an important branch of mineralogical science. The methods of detecting the different elements, and the characters which are thus furnished for the discrimination of minerals, are also of much value. This is especially true of the metallic ores and other substances, sought not as objects of curiosity, but for their economic qualities.

**Composition of Minerals.**

At present about sixty elements, or substances which have not been decomposed, are known. These are divided into metallic and non-metallic, a distinction of importance in mineralogy, though not always to be carried out with precision. The non-metallic elements are rarely of semimetallic aspect, and are bad conductors of heat and electricity. Some are commonly gaseous—oxygen, hydrogen, nitrogen, chlorine, and fluorine; one fluid—bromine; the others solid—carbon, phosphorus, sulphur, boron, silicon, and iodine. The metallic elements are, except mercury, solid at usual temperatures, have generally a metallic aspect, and are good conductors of heat and electricity. They are divided into light and heavy metals, the former with a specific gravity under 5, and a great affinity for oxygen, and again distinguished as either alkali-metals, potassium (or kalium), sodium (or natrium), lithium, barium, strontium, and calcium;—or earth-metals, magnesium, lanthanum, yttrium, glucinium, aluminium, zirconium, silicium. The heavy metals, with a specific gravity above 5, are divided into noble, which can be reduced, or separated from oxygen, by heat alone; and ignoble, whose affinity for oxygen renders them irreducible without other agents. Some of the latter are brittle and difficultly fusible,—thorium, titanium, tantalum (columbium), tungsten (wolframium), molybdenum, vanadium, chromium, uranium, manganese, and cerium; others are brittle and easily fusible or volatile—arsenic, antimony, tellurium, and bismuth; and others malleable—zinc, cadmium, tin, lead, iron, cobalt, nickel, and copper. The noble metals are,—quicksilver, silver, gold, platinum, palladium, rhodium, iridium, and osmium.

All the chemical combinations observed in the mineral kingdom follow the law of definite proportions; that is, two elements always combine either in the same proportion, or so that the quantity of the one is multiplied by two, three, four, or some other definite number seldom very large. As the same law prevails throughout the whole range of elements, by assuming any one, usually hydrogen or oxygen, as unity or 1, and determining from experiment the simple proportion in which the others combine with it, a series of numbers is obtained which also expresses the proportions in which all these elements combine with each other. These numbers, therefore, mark the combining proportions or equivalents, as they are named, of the elements. They are also named atomic weights, on the supposition that matter consists of definite atoms, and that its combinations consist of one atom (or sometimes two atoms) of one substance, with one, two, three, or more atoms of another. This theory is not free from difficulties, but the language is often convenient. To designate the elements chemists generally employ the first letter or letters of their Latin names. These signs also indicate one atom or equivalent of the element. Thus, O means oxygen in the proportion of one atom; H, hydrogen in the same proportion; N, an atom of nitrogen; Na, an equivalent proportion of natrium or sodium. These signs and the equivalent weights are given in the following table, in one column of which hydrogen is taken as unity, in the other oxygen. The elements are arranged according to Berzelius, beginning with the most electro-positive, and ending with the most electro-negative. The above list includes ammonium, usually considered a compound body, and omits the two new metals, erbium and terbium.

All these elements occur in minerals, but not more than twenty are common, and only about twelve abundant. They are also very rare in their simple or uncombined state; only carbon in the diamond and graphite, sulphur, and about a dozen of the native metals, being thus known. More frequently minerals consist of two or more elements combined in accordance with those laws which prevail in inorganic compounds. The most important of these laws is that the combinations are binary; that is, that the elements unite in pairs, which may again unite either with another compound of two, or with a single element. Inorganic compounds also are generally distinguished from organic by their greater simplicity.

The following principles are observed in designating the combinations of these elementary substances:—For those of the first order the signs of the two components are conjoined, and the number of atoms or equivalents of each expressed by a number following the sign like an algebraic exponent. Thus, SO, SO₂, SO₃, are the combinations of one atom sulphur with one, two, and three atoms of oxygen; FeS, FeS₂, of one atom of iron with one or two of sulphur. But as combinations with oxygen and sulphur are very numerous in the mineral kingdom, Berzelius, to whom science is indebted for this system of signs, marks the atoms of oxygen by dots over the sign of the other element, and those of sulphur by an accent; the above compounds being then designated thus—S̄, S̄, S̄, and Fē, Fē. In some cases two atoms of a base combine with three or five of oxygen or sulphur, as AlO₃, FeS₂. In such cases Berzelius marks the double atom by a line drawn through the sign of the single atom; thus, Al₂ is two atoms aluminium with three of oxygen or alumina; Cu₂, two of copper with one of oxygen or oxide of copper. Where a number is prefixed to the sign like a coefficient in algebra it includes both elements of the combination; thus H₂ is one atom water, 2 H₂ two; CaC₂ is one atom carbonate of lime, 2 CaC₂ two atoms, including of course two of calcium, two of carbon, and six of oxygen.

The most common and important binary compounds are those with oxygen, contained in the following table, with their signs, atomic numbers, and amount of oxygen in 100 parts. The more electro-negative are named acids, which are often soluble in water, and then render blue vegetable colours red. The more electro-positive are named oxides or bases, and show great affinity or attractive power for the former. The most powerful are the alkaline bases, which are colourless and soluble in water; less powerful are the earths, also colourless, but insoluble in water:

### Table II.—Binary Compounds with Oxygen

| Name | Sign | Atomic Weight | Oxy. in 100 Parts | |-----------------------|------|---------------|------------------| | Alumina | Al | 54-1 | 642-33 | | Antimony oxide | Sb | 145 | 1829-2 | | Antimonious acid | Sb | 154 | 1929-2 | | Antimontic acid | Sb | 162 | 2029-2 | | Arsenious acid | As | 99 | 1240-08 | | Arsenic acid | As | 115 | 1440-08 | | Baryta | Ba | 76-6 | 956-88 | | Bismuth peroxide | Bi | 232 | 2900-00 | | Boracic acid | B | 34-8 | 438-20 | | Carbonic acid | C | 22 | 275-0 | | Cerium protoside | Ce | 54 | 674-72 | | Peroxide | Ce | 116 | 1449-39 | | Chromium oxide | Cr | 76-6 | 956-78 | | Chromic acid | Cr | 50-3 | 628-39 | | Cobalt protoside | Co | 38 | 475 | | Copper suboxide (red) | Cu | 71-4 | 891-39 | | Copper protoside | Cu | 99-7 | 495-69 | | Glacina | G | 38 | 490-05 | | Iron protoside | Fe | 36 | 450-57 | | Iron protoside (red) | Fe | 100-054 | 29-97 | | Lead protoside | Pb | 112 | 1394-50 | | Lime or Calcite | Ca | 15 | 186-9 | | Lithia | Li | 21 | 254-50 | | Magnesia | Mg | 36 | 445-89 | | Manganese protoside | Mn | 80 | 991-77 | | Molybdic acid | Mo | 70 | 875-83 | | Nickel protoside | Ni | 37 | 462-28 | | Nitric acid | N | 54 | 675-06 | | Phosphoric acid | P | 71 | 892-28 | | Potassa | K | 47-2 | 588-866 | | Silica (Gmelin) | Si | 31 | 387-5 | | Silica (Berzelius) | Si | 46-2 | 577-31 | | Soda | Na | 31-2 | 390-90 | | Strontia | Sr | 52 | 647-29 | | Sulphuric acid | S | 40 | 500-75 | | Tantalic acid | Ta | 209 | 2607-43 | | Thorina | Th | 67-6 | 844-90 | | Tin protoside | Sn | 75 | 892-29 | | Titanic acid | Ti | 41 | 503-88 | | Tungstic acid | W | 116 | 1450-78 | | Uranium protoside | U | 68 | 842-84 | | Vanadic acid | V | 144 | 1702-72 | | Water | H | 9 | 112-48 | | Ytria | Y | 40 | 502-51 | | Zinc oxide | Zn | 40-2 | 506-59 | | Zirconia | Zr | 30-4 | 114-2 |

Note.—In this table double atoms are indicated by the black letters, or Al = Al, Fe = Fe, &c. Similar to the compounds of oxygen are those with sulphur, usually named sulphurets, and considered analogous to the oxidized bases. A few of more electro-negative character, resembling acids, have been distinguished as sulphides. Some other compounds have been named haloid salts, and consist of certain electro-negative elements, combined with electro-positive ones, as bases.

Many of these combinations occur as independent species in the mineral kingdom, especially those with oxygen and sulphur. Thus the most abundant of all minerals, quartz, is an oxide, and corundum is of similar nature. Many oxides of the heavy metals, as of iron, tin, copper, and antimony; and some super-oxides, as of lead and manganese (pyrolusite),—are very common. Compounds with sulphur also abound, and either as sulphides, with the character of acids, like realgar, orpiment, and stibnite; oras sulphurets, resembling bases, like galena, argentite, and pyrite. Less frequent are haloid salts, with chlorine and fluorine, as common salt and fluorspar; and still rarer those with iodine and bromine. On the other hand, metallic alloys, or combinations of electro-negative with electro-positive metals, are far from uncommon, especially those with arsenic, tellurium, or antimony.

Combinations of these binary compounds with each other are still more common, the greater number of minerals being composed of an acid and base. By far the greatest number are oxygen-salts, distinguished by giving to the acid the termination ate; thus sulphate of lead, silicate of lime, and in like manner numerous carbonates, phosphates, arseniates, aluminates. The sulphur-salts (two metals combined with sulphur, and again combined with each other) are next in number, and perform a most important part in the mineral kingdom. The hydrates, or combinations of an oxide with water, are also common, and much resemble the oxygen salts, the water sometimes acting as an electro-positive, at other times as an electro-negative element.

Combinations of a higher order are likewise common, especially the double salts, or the union of two salts into a new body; and even these again with water, as alum and many hydrous silicates. The chemical formula for these compound salts are formed by writing the signs of the simple salts with the sign of addition between them: thus CaC + MgC, Ca, carbonate of lime and carbonate of magnesia, or brown spar; HSi + KSi, or orthoclase; 3NaF + AlF, or cryolite, composed of three compound atoms of fluorine and sodium united to one compound atom, consisting of three of fluorine and two of aluminium.

Influence of the Chemical Composition on the External Characters of Minerals.

That the characters of the compound must in some way or other depend on those of its component elements seems, as a general proposition, to admit of no doubt. Hence it might be supposed possible, from a knowledge of the composition of a mineral, to draw conclusions in reference to its form and other properties; but practically this has not yet been effected. The distinction between the mineralizing and mineralizable, or the forming and formed, elements, lies at the foundation of all such inquiries. Certain elements in a compound apparently exert more than an equal share of influence in determining its physical properties. Thus the more important non-metallic elements, as oxygen, sulphur, chlorine, fluorine, are remarkable for the influence they exert on the character of the compound. The sulphurets, for example, have more similarity among themselves than the various compounds of one and the same metal with the non-metallic bodies. Still more generally it would appear that the electro-negative element in the compound is the most influential, or exerts the greatest degree of active forming power. After the non-metallic elements the brittle, easily fusible metals rank next in power; then the ductile igneous metals; then the noble metals; then the brittle, difficultly fusible; and last of all, the metals of the earths and alkalies.

It is sometimes stated that each particular substance can crystallize only in one particular form or series of forms. This is, however, only partially true; and sulphur, for instance, which usually crystallizes in the rhombic system, when melted may form monoclinohedric crystals. This property is named dimorphism; and hence the same chemical substance may form two, or even more, distinct bodies or mineral species. Thus carbon in one form is the diamond, in another graphite; carbonate of lime appears as calc-spar or aragonite; the bisulphuret of iron as pyrite and marcasite. An example of trinorphism occurs in the titanic acid, forming the three distinct species, anatase, rutile, and brookite. Even the temperature at which a substance crystallizes influences its forms, and so far its composition, as seen in aragonite, Glauber salt, natron, and borax.

Still more important is the doctrine of isomorphism, designating the fact that two or more simple or compound substances crystallize in one and the same form; or often in forms which, though not identical, yet approximate very closely. This similarity of form is generally combined with a similarity in other physical properties. Among minerals that crystallize in the tesserai form, isomorphism is of course common and perfect, there being no diversity in the dimensions of the primary form; but for this very reason it is of less interest. It is of more importance among mono-axial crystals, the various series of which are separated from each other by differences in the proportion of the primary form. In these perfect identity is seldom observed, but only very great similarity.

The more important isomorphic substances are the following:

I. Simple substances: (1.) Fluorine and chlorine. (2.) Sulphur and selenium. (3.) Arsenic, antimony, tellurium. (4.) Cobalt, iron, nickel. (5.) Copper, silver, quicksilver, gold (?)

II. Combinations with oxygen: (1.) Of the formula R. (a.) Lime, magnesia, protoxide of iron, protoxide of manganese, oxide of zinc, oxide of nickel, oxide of cobalt, potassa, soda. (b.) Lime, baryta, strontia, lead-oxide. (2.) Of the formula R. (a.) Alumina, peroxide of iron, peroxide of manganese, oxide of chromium. (b.) Antimony oxide, arsenious acid. (3.) Formula R. Tin-oxide, titanium-oxide. (4.) Formula R. Phosphoric acid, arsenic acid. (5.) Formula R. (a.) Sulphuric acid, selenic acid, chromic acid, manganese acid. (b.) Tungstic acid, molybdic acid.

III. Combinations with sulphur: (1.) Formula R. Sulphuret of iron Fe', and sulphuret of zinc Zn'. (2.) Formula R. Sulphuret of antimony Sb", and sulphuret of arsenic As". (3.) Formula R. Sulphuret of copper Cu, and sulphuret of silver Ag'.

These substances are named vicarious, from the singular property that in chemical compounds they can mutually replace each other in indefinite proportions, and very often without producing any important change in the form or other physical properties. But there are numerous instances among the silicates, where the mutual replacement of the isomorphous bodies, especially when the oxides of the heavy metals come in the room of the earths and alkalies, exerts a most essential influence on the external aspect of the species; particularly in regard to colour, specific gravity, and transparency. The varieties of hornblende, augite, garnet, epidote, and many other minerals, are remarkable proofs of this influence. This intermixture of isomorphic elements confers many valuable properties on minerals, and to it this department of nature owes much of its variety and beauty. Without the occasional presence of the colouring substances, especially the oxides of iron and manganese, the non-metallic combinations would have exhibited a very monotonous aspect. It is also remarkable that in some silicates the substitution of a certain portion of the metallic oxides for the earthy bases seems to be almost a regular occurrence; whilst in others, as the felspars and zeolites, this rarely happens. This fact is often of great economic importance, as drawing attention to important elements often combined with others of less value. Thus iron oxide and chrome oxide, sulphuret of copper and sulphuret of silver, nickel and cobalt, may be looked for in connection.

The general chemical formula for such compounds is formed by writing R (radicle or basis) for the whole isomorphic elements; and in special instances to place their signs either one below the other, connected by a bracket, or, as is more convenient, to inclose them in brackets one after the other, separated by a comma. Thus the general sign for the garnet is $R^3 Si^4 + R^2 Si$, which, when fully expressed, becomes $(Ca, Fe, Mn)^3 Si^4 + (Al, Fe) Si$.

Chemical Reaction of Minerals.

The object of the chemical examination of minerals is the discovery of those elementary substances of which they consist. This examination is named qualitative when the nature of the elements alone, quantitative when also their relative amount, is sought to be determined. Mineralogists are in general content with such an examination as will discover the more important elements, and which can be carried on with a simple apparatus, and small quantities of the substance investigated. The indications thus furnished of the true character of the mineral are, however, frequently of high importance. Two methods of testing minerals are employed, the one by heat chiefly applied through the blowpipe, the second by acids and other reagents in solution.

Use of the Blowpipe.

The blowpipe in its simplest form is merely a conical tube of brass or other metal, curved round at the smaller extremity, and terminating in a minute circular aperture not larger than a fine needle. Other forms have been proposed, one of the most useful being a cone of tin open for the application of the mouth at the smaller end, and with a brass or platina beak projecting from the side near the other or broad end. With this instrument a stream of air is conveyed from the mouth to the flame of a lamp or candle, so that this can be turned aside, concentrated, and directed upon any small object. The flame thus acted on consists of two parts,—the one nearest the beak of the blowpipe forming a blue obscure cone, the other external to this being of a shining yellow or reddish-yellow colour. The blue cone consists of the inflammable gases not yet fully incandescent, and the greatest heat is just beyond its point, where this is fully effected. The blue flame still needs oxygen for its support, and consequently tends to withdraw it from any body placed within its influence, and is named the reducing flame. At the extremity of the yellow cone, on the other hand, the whole gases being consumed, and the external air having free access, bodies are combined with oxygen, and this part is named the oxidising flame. Their action being so distinct, it is of great importance for the student to learn to distinguish accurately these two portions of the flame. This is best done by experimenting on a piece of metallic tin, which can only be kept pure in a good reducing flame, and acquires a white crust when acted on by the oxidising flame.

The portion of the mineral to be examined should not be larger than a peppercorn, or a fine splinter a line or two long. It is supported in the flame either by a pair of fine pincers pointed with platinum, or on slips of platinum-foil, or on charcoal. Platinum is best for the siliceous minerals, whereas for metallic substances charcoal must be employed. For this purpose solid uniform pieces are chosen, and a small cavity formed in the surface in which the mineral to be tested can be deposited.

In examining a mineral by heat, it should be first tested alone, and then with various reagents. When placed alone in a matrass or tube of glass closed at one end, and heated over a spirit lamp, water or other volatile ingredients, mercury, arsenic, tellurium, often sulphur, may readily be detected, being deposited in the cooler part of the tube, or, like fluorine, acting on the glass. It may next be tried in an open tube of glass, through which a more or less strong current of air passes according to the inclination at which the tube is held, so that volatile oxides or acids may be formed; and in this way the chief combinations of sulphur, selenium, tellurium, and arsenic are detected. On charcoal, in the reducing flame, arsenic, and in the oxidising flame, selenium or sulphur, are shown by their peculiar odour; antimony, zinc, lead, and bismuth leave a mark or coloured ring on the charcoal; and other oxides and sulphures are reduced to the pure metal. On charcoal or in the platinum pincers the fusibility of minerals is tested, and some other phenomena should be observed—as whether they intumesce (bubble up), effervesce, give out fumes, become shining, or impart a colour to the flame. The colour is seen when the assay is heated at the point of the inner flame, and is—

Reddish-yellow, from soda and its salts; Violet, from potash and most of its salts; Red, from lime, strontia, and lime; Green, from baryta, phosphoric acid, boracic acid, molybdic acid, copper oxide, and tellurium oxide; Blue, from chloride of copper, bromide of copper, selenium, arsenic, antimony, and lead.

The fusibility, or ease with which a mineral is melted, should also be observed; and to render this character more precise, von Kobell has proposed this scale:—(1.) Antimony glance, which melts readily in the mere candle flame; (2.) Natrolite, which in fine needles also melts in the candle flame, and in large pieces readily before the blowpipe; (3.) Almandine (garnet from Zillertal), which does not melt in the candle flame even in fine splinters, but in large pieces before the blowpipe; (4.) Strahlstein (hornblende from Zillertal) melts with some difficulty, but still more readily than (5.) Orthoclase (or adularia felspar); and (6.) Bironzite or diaglass, of which only the finest fibres can be rounded by the blowpipe. In employing this scale, fine fragments of the test minerals and of that to be tried, and nearly of equal size, should be exposed at the same time to the flame. A more common mode of expressing fusibility is to state whether it is observable in large or small grains, in fine splinters, or only on sharp angles. The result or product of fusion also yields important characters, being sometimes a glass, clear, opaque, or coloured; at other times an enamel, or a mere slag.

The most important reagents for testing minerals with the blowpipe are the following:—(1.) Soda (the carbonate), acting as a flux for quartz and many silicates, and especially for reducing the metallic oxides. For the latter purpose, the assay (or mineral to be tried) is reduced to powder, kneaded up with moist soda into a small ball, and placed in a cavity of the charcoal. Very often both the soda and assay sink into the charcoal, but by continuing the operation they either again appear on the surface, or, when it is completed, the charcoal containing the mass is finely pounded and washed away with water, when the reduced metal is found in the bottom of the vessel. (2.) Borax (bichromate of soda) serves as a flux for many minerals, which are best fused in small splinters on platinum wire. The borax when first exposed to the flame swells up or intumesces greatly, and it should therefore be first melted into a small bead, in which the assay is placed. During the process the student should observe whether the assay melts easily or difficulty, with or without effervescence, what colour it imparts to the product both when warm and when cold, and also the effect both of the oxidizing and reducing flames. (3.) Microcosmic salt, or salt of phosphorus (phosphate of soda and ammonia) is specially important as a test for metallic oxides, which exhibit far more decided colours with it than with borax. It is also a useful reagent for many silicates, whose silica is separated from the base and remains undissolved in the melted salt. (4.) Solution of cobalt (nitrate of cobalt dissolved in water), or dry oxalate of cobalt, serve as tests of alumina, magnesia, and zinc oxide.

In examining minerals in the moist way, the first point to be considered is their solubility, of which three degrees may be noted: (1) minerals soluble in water; (2) minerals soluble in hydrochloric or nitric acid; and (3) those unaffected by any of these fluids. The minerals soluble in water are either acids (almost only the horacic acid or sassolin and the arsenious acid), or oxygen or haloid salts. These are easily tested, one part of the solution being employed to find the electro-positive element or basis, the other the electro-negative or acid.

Minerals insoluble in water may next be tested with the above acids; the nitric acid being preferable when it is probable, from the aspect of the mineral or its conduct before the blowpipe, that it contains an alloy, a sulphuret, or arseniate of some metal. In this manner the carbonic, phosphoric, arsenic, and chromic acid salts, many hydrous and anhydrous silicates, many sulphures, arseniates, and other metallic compounds, are dissolved, so that further tests may be employed.

The minerals insoluble either in water or these acids are sulphur, graphite, cinnabar, some metallic oxides, some sulphates, and compounds with chlorine and fluorine, and especially quartz, and various silicates. For many of these no test is required, or those furnished by the blowpipe are sufficient. The silicates and others may be fused with four times their weight of anhydrous carbonate of soda when they are rendered soluble, so that further tests may be applied.

Chemical Reaction of the more Important Elements.

It is not intended in this place to describe the chemical nature of the elementary substances, and still less to enumerate the whole of those marks by which the chemist can detect their presence. Our object is limited principally to the conduct of minerals before the blowpipe, and to a few simple tests by which their more important constituents may be discovered by the student.

I.—NON-METALLIC ELEMENTS, AND THEIR COMBINATIONS WITH OXYGEN.

Nitric Acid.—Most of its salts detonate when heated on charcoal. In the closed tube they form nitrous acid, easily known by its orange colour and smell; a test more clearly exhibited when the salt is mixed with copper filings and treated with concentrated sulphuric acid. When to the solution of a nitrate, a fourth part of sulphuric acid is added, and a fragment of green vitriol placed in it, the surrounding fluid becomes of a dark brown colour.

Sulphur and its compounds, in the glass tube or on charcoal, form sulphurous acid, easily known by its smell. The minutest amount of sulphur or sulphuric acid may be detected by melting the pulverized assay with two parts soda and one part borax, and placing the head moistened with water on a plate of clean silver, which is then stained brown or black. Solutions of sulphuric acid give with chloride of barium a heavy white precipitate, insoluble in acids.

Phosphoric Acid.—Most combinations with this acid tinge the blowpipe flame green, especially if previously moistened with sulphuric acid. The experiment must be performed in the dark, when even three per cent. of the acid may be detected. If the assay is melted with six parts of soda, digested in water, filtered, and neutralized with acetic acid, the solution forms an orange-yellow layer round a crystal of nitrate of silver. This solution, with muriate of magnesia, forms a white crystalline precipitate.

Selenium and Selenic Acid are readily detected by the strong smell of decayed horse-radish, and leave a gray deposit with a metallic lustre on the charcoal.

Chlorine and its salts. When oxide of copper is melted with salt of phosphorus into a very dark-green bead, and an assay containing chlorine fused with this, the flame is tinged of a beautiful reddish blue colour, till all the chlorine is driven off. If very little chlorine is present, the assay is dissolved in nitric acid (if not soluble it must first be melted with soda on platinum wire), and the diluted solution gives, with nitrate of silver, a precipitate of chloride of silver, which is first white, but on exposure to the light becomes gradually brown, and at length black.

Iodine and its salts, treated like chlorine, impart a very beautiful bright-green colour to the flame; and heated in the closed tube with sulphate of potash, yield violet-coloured vapours. In solution it gives, with nitrate of silver, a precipitate similar to chlorine, but which is very difficultly soluble in ammonia. Its surest test is the blue colour it imparts to starch, best seen by pouring concentrated sulphuric acid over the mineral in a test tube which has a piece of paper or cotton covered with moist starch over its mouth.

Bromine and its salts, treated in the same manner with salt of phosphorus and oxide of copper, colour the blowpipe flame greenish blue. In the closed tube with nitrate of potassa they yield bromine vapours, known by their yellow colour and peculiar disagreeable smell. Treated with sulphuric acid, bromine in a few hours colours starch pomegranate-yellow.

Fluorine is shown by heating the assay with sulphate of potassa, in a closed tube with a strip of logwood paper in the open end. The paper becomes straw-yellow, and the glass is corroded. Another test is to heat the pulverized mineral with concentrated sulphuric acid in a shallow dish of platinum (or lead), over which a plate of glass covered with a coat of wax, through which lines have been drawn with a piece of sharp-pointed wood, is placed. If fluorine is present the glass is etched where exposed.

Boracic Acid.—The mineral alone, or moistened with sulphuric acid when melting, colours the flame momentarily green. If the assay be heated with sulphuric acid, and alcohol added, and set on fire, the flame is coloured green from the vapours of the boracic acid.

Carbon, pulverized and heated with saltpetre, detonates, leaving carbonate of potassa. Carbonic acid is not easily discovered with the blowpipe, but the minerals containing it effervesce in hydrochloric acid, and the colourless gas that escapes renders limmus paper red. In solution it forms a precipitate with lime-water, with is again dissolved with effervescence in acids.

Silica, before the blowpipe, alone is unchanged; is very slowly acted on by borax, very little by salt of phosphorus, but with soda melts entirely with a brisk effervescence into a clear glass. The silicates are decomposed by salt of phosphorus, the silica being left in the bead as a powder or a skeleton. Most of them melt with soda to a transparent glass. Some silicates are dissolved in hydrochloric acid, and this the more readily the more powerful the basis, the less proportion of silica, and the greater the amount of water they contain. Sometimes the acid only extracts the basis, leaving the silica as a powder or jelly; or the silica too is dissolved, and only gelatinizes on evaporation. The insoluble silicates may be first melted with some carbonate of an alkali, when the solution gelatinizes, and finally leaves a dry residuum of which the part insoluble in warm hydrochloric acid has all the properties of silica.

II.—THE ALKALIES AND EARTHS.

Ammonia, heated with soda in a closed tube, is readily known by its smell. Its salts, heated with solution of potassa, also yield the vapour, known from its smell, its action on turmeric paper, and the white fumes that rise from a glass tube tipped in hydrochloric acid held over it.

Soda imparts a reddish-yellow colour to the external flame when the assay is fused or kept at a strong red heat. In solution it yields no precipitate with chloride of platinum or sulphate of alumina.

Lithia is best recognised by the beautiful carmine-red colour it imparts to the flame during the fusion of a mineral containing it in considerable amount. Where the proportion is small, the colour appears if the assay be mixed with 1 part flour spar and 1/4 parts sulphate of potassa. In concentrated solutions it forms a precipitate with the phosphate and carbonate of soda, but none with bichloride of platinum, sulphate of alumina, or acetic acid.

Potassa gives a violet colour to the external cone, when the assay is heated at the extremity of the oxidising flame. The presence of lithia or soda, however, disturbs this reaction. It may still be discovered by melting the assay in borax glass coloured brown by nickel oxide, which is changed to blue by the potassa. In concentrated solutions of potassa the bichloride of platinum gives a citron-yellow precipitate; acetic acid a white, granular precipitate; and sulphate of alumina, after some time, a deposit of alum-crystals.

Baryta.—The carbonate of this earth melts easily to a clear glass, milk-white when cold; the sulphate is very difficultly fusible. Both strongly heated at the point of the blue flame impart a green tinge to the outer flame. When combined with silica it cannot be well discovered by the blowpipe. In solution, salts of baryta yield, with sulphuric acid or solution of sulphate of lime, immediately a fine white precipitate insoluble in acids or alkalies.

Strontia, the carbonate, even in thin plates, only melts on the edges, and forms cauliflower-like projections of dazzling brightness; the sulphate melts easily in the oxidising flame, and in the reducing flame is changed into sulphuret of strontium, which, dissolved in hydrochloric acid, and evaporated to dryness, gives a fine carmine-red colour to the flame of alcohol. Strontia in solution gives a precipitate with sulphuric acid, or with sulphate of lime, but not immediately.

Lime.—The carbonate is rendered caustic by heat, when it has alkaline properties, and readily absorbs water. The sulphate in the reducing flame changes to the sulphuret of calcium, which is also alkaline. Sulphuric acid precipitates lime only from very concentrated solutions; oxalic acid even from very weak ones; and silico-hydrofluoric acid not at all. As baryta and strontia also form precipitates with the first two reagents, they must previously be separated by sulphate of potassa. Chloride of calcium tinges the flame of alcohol yellowish-red.

Magnesia, alone, or as a hydrate, a carbonate, and in some other combinations, when ignited with solution of cobalt, or the oxalate of cobalt, assumes a light-red tint. It is not precipitated from a solution either by sulphuric acid, oxalic acid, or silico-hydrofluoric acid; but phosphoric acid, with ammonia, throws down a white crystalline precipitate of phosphate of ammonia and magnesia.

Alumina alone is infusible. In many combinations, when ignited with solution of cobalt, it assumes a fine blue colour. It is thrown down by potassa or soda as a white voluminous precipitate, which in excess of the alkali is easily and completely soluble, but is again precipitated by muriate of ammonia. Carbonate of ammonia also produces a precipitate which is not soluble in excess.

Glucina, Ytrria, Zirconia, and Thorina are not properly distinguished by blowpipe tests, though the minerals in which they occur are well marked in this way. In solution glucina acts with potassa like alumina; but the precipitate with carbonate of ammonia is again soluble, with excess of the alkali, and the two earths may thus be separated. Ytrria is precipitated by potassa, but is not again dissolved by excess of the alkali. With carbonate of ammonia it acts like glucina. It must be observed, however, that the substance formerly named ytrria is now considered a mixture of this earth with the oxides of erbium, terbium, and lanthanum. Zirconia acts with potassa like ytrria, and with carbonate of ammonia like glucina. Concentrated sulphate of potassa throws down a double salt of zirconia and potassa, which is very little soluble in pure water.

III.—THE METALS.

Arsenic and its sulphuret on charcoal yield fumes, with a smell like garlic, and sublime in the closed tube. The greater number of alloys of arsenic in the reducing flame leave a white deposit on the charcoal; or where it is in larger proportion, give out grayish-white fumes with a smell of garlic. Some alloys also yield metallic arsenic in the closed tube. In the open tube all of them yield arsenious acid, and those containing sulphur also sulphurous fumes. Many arsenic acid salts emit evident odours of arsenic when heated on charcoal with soda; and some sublime metallic arsenic when heated with pulverized charcoal in the closed tube.

Antimony melts easily on charcoal, emitting dense white fumes, and leaving a ring of white crystalline oxide on the support. In the closed tube it does not sublime, but burns in the open tube with white smoke, leaving a sublimate on the glass, which is easily driven from place to place by heat. Most of its compounds, with sulphur or with the other metals, show similar reaction. Antimony oxide on charcoal melts easily, fumes, and is reduced, colouring the flame pale greenish-blue.

Bismuth melts easily, fumes, and leaves a yellow oxide on the charcoal. In the closed tube it does not sublime, and in the open tube scarcely fumes, but is surrounded by the fused oxide, dark-brown when warm, and bright-yellow when cold. Its oxides are easily reduced. A great addition of water produces a white precipitate from its solution in nitric acid.

Tellurium fumes on charcoal, and becomes surrounded by a white mark with a reddish border, which, when the reducing flame is turned on it, disappears with a bluish-green light. In the closed tube tellurium gives a sublimate of the gray metal; and in the open tube produces copious fumes, and a white powder which can be melted into small clear drops.

Mercury in all its combinations is volatile, and yields a metallic sublimate when heated alone, or with tin or soda in the closed tube.

Zinc, when heated with soda on charcoal, forms a deposit, which, when warm, is yellow; when cold, white; is tinged of a fine green by solution of cobalt, and is not further volatile in the oxidating flame. In solution zinc is precipitated by potassa as a white gelatinous hydrate, easily redissolved in the excess of the alkali.

Tin forms a white deposit on the charcoal behind the assay, which takes a bluish-green colour with the solution of cobalt. The oxide is easily reduced by soda.

Lead forms a sulphur-yellow deposit with a white border on the charcoal when heated in the oxidating flame, and with soda is easily reduced. The solutions of its salts are colourless, but give a black precipitate with sulphuretted hydrogen; with sulphuric acid a white, and with chromate of potassa a yellow, precipitate.

Cadmium produces, with soda, a reddish-brown or orange-yellow ring, with iridescent border on the charcoal, and also on platinum-foil.

Manganese alone, melted with borax or salt of phosphorus on the platinum wire in the oxidating flame, forms a fine amethystine glass, which becomes colourless in the reducing flame. In combination with other metals, the pulverized assay mixed with two or three times as much soda, and melted in the oxidating flame on platinum-foil, forms a bluish-green glass. Potassa or ammonia throws down from solutions of its salts a white hydrate, which in the air becomes gradually dark-brown.

Cobalt, melted with borax in the oxidating flame, gives a beautiful blue glass. Minerals of metallic aspect must be first roasted on charcoal. The salts of protoxide of cobalt form bright-red solutions, from which potassa throws down a blue flaky hydrate, which becomes olive-green in the air.

Nickel, the assay, first roasted in the open tube and on charcoal, produces in the oxidating flame, with borax, a glass, which hot, is reddish or violet-brown; when cold, yellowish or dark red; and by the addition of saltpetre changes to blue. In the reducing flame the glass appears gray. With salt of phosphorus the reaction is similar, but the glass is almost colourless when cold. The salts in solution have a bright-green colour, and with potassa form a green precipitate of hydrated nickel-oxide, which is unchanged in the air.

Copper may in most cases be discovered by melting the assay (if apparently metallic, first roasted) with borax or salt of phosphorus in the oxidating flame, when an opaque reddish-brown glass is produced, a small addition of tin aiding in the result. In the reducing flame the glass, when warm, is green; when cold, blue. With soda metallic copper is produced. A small proportion of copper may often be detected by heating the assay, moistened with hydrochloric acid, in the oxidating flame, which is then tinged of a beautiful green colour. Solutions of its salts are blue or green, and produce a brownish-black precipitate, with sulphuretted hydrogen. Ammonia at first throws down a pale-green or blue precipitate, but in excess produces a very fine blue colour.

Silver in the metallic state is at once known, and from many combinations can be readily extracted on charcoal with soda. From its solution in nitric acid silver is thrown down by hydrochloric acid as a white chloride, which in the light soon becomes black, is soluble in ammonia, and can again be precipitated from this solution by nitric acid as chloride of silver.

Gold, when pure, is readily known, and is easily separated from its combinations with tellurium on charcoal. If the grain is white, it contains more silver than gold, and must then be heated in a porcelain capsule with nitric acid, which gives it a black colour, and gradually removes the silver, if the gold is only a fourth part or less. If the proportion of gold is greater, the nitro-chloric acid must be used, which then removes the gold. From its solution in this acid the protoclirhode of tin throws down a purple precipitate (purple of Cassius), and the sulphate of iron, metallic gold.

Platinum, and the metals usually found with it, cannot be separated from each other by heat. Only the Osmitum-iridium strongly heated in the closed tube with saltpetre is decomposed, forming osmium acid, known from its peculiar pungent odour. The usual mixture of platinum grains is soluble in nitro-chloric acid, leaving osmium-iridium. From this solution the platinum is thrown down by sal-ammonia as a double chloride of platinum and ammonium. From the solution evaporated, and again diluted, with cyanide of mercury, the palladium separates as cyanide of palladium. The rhodium may be separated by its property of combining with fused bisulphate of potassa, which is not the case with platinum or iridium.

Cerium, when no iron-oxide is present, produces, with borax and salt of phosphorus, in the oxidating flame, a red or dark-yellow glass, which becomes very pale when cold, and colourless in the reducing flame. Lanthanum oxide forms a white colourless glass; didymium a dark amethystine glass.

Iron, the peroxide and hydrated peroxide, become black and magnetic before the blowpipe, and form, with borax or salt of phosphorus, in the oxidating flame, a dark-red glass, becoming bright-yellow when cold; and in the reducing flame, especially on adding tin, an olive-green or mountain-green glass. The peroxide colours a bead of borax containing copper oxide bluish-green; the protoxide produces red spots. Salts of protoxide of iron form a green solution, from which potassa or ammonia throws down the protoxide as a hydrate, which is first white, then dirty-green, and finally yellowish-brown. Carbonate of lime produces no precipitate. The salts of the peroxide, on the other hand, form yellow solutions from which the peroxide is thrown down by potassa or ammonia as a flaky-brown hydrate. Carbonate of lime also causes a precipitate.

Chromium forms, with borax or salt of phosphorus, a glass, fine emerald-green when cold, though when hot often yellowish or reddish. Its solutions are usually green, and the metal is thrown down by potassa as a bluish-green hydrate, again dissolved in excess of the alkali. The chrome in many minerals is very certainly discovered by melting the assay with three times its bulk of saltpetre, which, dissolved in water, gives with acetate of lead a yellow precipitate.

Vanadium, melted on platinum wire with borax or salt of phosphorus, gives a fine green glass in the reducing flame, which becomes yellow or brown in the oxidating flame, distinguishing it from chrome.

Uranium, with salt of phosphorus, forms in the oxidating flame a clear yellow; in the reducing flame a fine green glass. With borax its reaction is similar to that of iron.

Molybdenum forms in the reducing flame, with salt of phosphorus, a green; with borax, a brown glass.

Tungsten or Wolfram forms, with salt of phosphorus, in the oxidating flame, a colourless or yellow, in the reducing flame, a very beautiful blue glass, which appears green when warm. When accompanied by iron the glass is blood-red, not blue. Or melt the assay five times as much soda in a platinum spoon, dissolve it in water, filter, and decompose the result with hydrochloric acid, which throws down the tungstic acid, which is white when cold, but citron-yellow when heated.

Tantalium, as tantalic acid, is readily dissolved by salt of phosphorus, and in large quantity into a colourless glass, which does not become opaque in cooling, and does not acquire a blue colour from solution of cobalt. Or fuse the assay with two times as much saltpetre, and three times as much soda, in a platinum spoon; dissolve this, filter, and decompose the fluid by hydrochloric acid: the tantalic acid separates as a white powder, which does not become yellow when heated.

Titanium in anatase, rutile, brookite, and titanite, is shown by the assay forming, with salt of phosphorus, in the oxidating flame, a glass which is and remains colourless; in the reducing flame, a glass which appears yellow when hot, and whilst cooling passes through red into a beautiful violet. When iron is present, however, the glass is blood-red, but is changed to violet by adding tin. When titanate of iron is dissolved in hydrochloric acid, and the solution boiled with a little tin, it acquires a violet colour from the oxide of titanium. Heated with concentrated sulphuric acid, the titanate of iron produces a blue colour.

**Chap. IV.—Classification of Minerals.**

A mineral species was formerly defined as a natural inorganic body, possessing a definite chemical composition and peculiar external form. The account given of these properties shows that the form of a mineral species comprehends not only the primary or fundamental figure, but all those that may be derived from it by the laws of crystallography. Irregularities of form arising from accidental causes, or that absence of form which results from the limited space in which the mineral has been produced, do not destroy the identity of the species. Even amorphous masses, when the chemical composition remains unaltered, are properly classed under the same species, as the perfect crystal.

The definite chemical composition of mineral species must be taken with equal latitude. Pure substances, such as they are described in works on chemistry, are very rare in the mineral kingdom. In the most transparent quartz crystals traces of alumina and iron oxide can be detected; the purest spinel contains a small amount of silica, and the most brilliant diamond, consumed by the solar rays, leaves some ash behind. Such non-essential mixtures must be neglected, or each individual crystal would form a distinct mineral species. The isomorphous elements introduce a wider range of varieties, and render the limitation of species more difficult. Carbonate of lime, for instance, becomes mixed with carbonate of magnesia or of iron in almost innumerable proportions; and the latter substances also with the former. Where these mixtures are small in amount, variable in different specimens, and do not greatly affect the form or physical characters of the predominant element, they may safely be neglected, and the mineral reckoned to that species with which it most closely agrees. Where, however, the mixture is greater, and the two substances are frequently found in definite chemical proportions, these compounds must be considered as distinct species, especially should they also show differences in form and other external characters.

Amorphous minerals with definite composition must also be considered as true species. But when they show no definite composition, as in many substances classed as clays and ochres, they cannot be accounted true mineral species, and properly ought not to be included in a treatise on mineralogy. Some of them, however, from their importance in the arts, others from other circumstances, have received distinct names and a kind of prescriptive right to a place in mineralogical works, from which they can now scarcely be banished. Many of them are properly rocks, or indefinite combinations of two or more minerals; others are the mere products of the decomposition of such bodies. Their number is of course indefinite, and their introduction tends much to render mineralogy more complex and difficult, and to destroy its scientific character.

In collecting the species into higher groups, and arranging them in a system, several methods have been pursued. Some, like Mohs, have looked only at the external characters, and asserted that they alone were sufficient for all the purposes of arranging and classifying minerals. Others, led by Berzelius, have, on the contrary, taken chemistry as the foundation of mineralogy, and clasped the species by their composition, without reference to form or physical characters.

Neither system can be exclusively adopted, and a natural classification of minerals should take into account all their characters, and that in proportion to their relative importance. Among these the chemical composition undoubtedly holds a high rank, as being that on which the other properties will probably be ultimately found to depend. Next in order is their crystalline form, especially as exhibited in cleavage; and then their other characters of gravity, hardness, and tenacity. But the properties of minerals are as yet far from showing that subordination and co-relation which has been observed in the organic world, where the external forms and structures have a direct reference to the functions of the living being. Hence even when all the characters are taken into account, there is not that facility in classifying the mineral that is presented by the other kingdoms of nature. Many, or rather most, of the species stand so isolated that it is scarcely possible to find any general principle on which to collect them into larger groups, especially such groups as, like the natural families of plants and animals, present important features of general resemblance, and admit of being described by common characteristics. Certain groups of species are indeed united by such evident characters, that they are found together in almost every method; but other species are not thus united, and the general order of arrangement is very uncertain. Hence, though some classifications of very considerable merit have been proposed, no natural system of minerals commanding general assent has yet appeared.

The arrangement followed in this treatise is chiefly founded on that proposed by Professor Weiss of Berlin. We have, however, made considerable changes, which the progress of the science and the more accurate knowledge of many species require. This classification appears to us to come nearer than any other we have seen to a natural system, which in arranging and combining objects takes account of all their characters, and assigns them their place, from a due consideration of their whole nature, and is thus distinguished from artificial systems, which classify objects with reference only to one character.

Besides species, two higher grades in classification seem sufficient at once to exhibit the natural relations, and to facilitate an easy and complete review of the species composing the mineral kingdom. These are families and orders. In forming the families those minerals are first selected which occupy the more important place in the composition of rocks, and consequently in the crust of the globe. Thus quartz, felspar, mica, hornblende, garnet, among siliceous minerals; calc-spar, gypsum, rock-salt, less so fluor spar and heavy spar, among those of saline composition, stand out prominently as the natural centres or representatives of so many distinct families. To these certain metallic minerals, as iron pyrites, lead-glanz or galena, blende, magnetic iron ore, the sparry iron ore, and a few more, are readily associated as important families. But the minerals thus geologically distinguished are not sufficient to divide the whole mineral kingdom into convenient sections, and additional groups must be selected from the peculiarity of their natural-historical or chemical properties. Thus the zeolites are easily seen to form such a natural group. The precious stones or gems also, notwithstanding their diverse chemical composition, must ever appear a highly natural family, when regarded as individual objects. Their great hardness, tenacity, high specific gravity without the metallic aspect, their brilliant lustre, transparent purity, and vivid colours—all mark them out as a peculiar group. Only the diamond, which might naturally seem to take the chief place in this class, differs so much, not only in elementary composition, but in physical properties, that it must be assigned to a diverse place.

Round these species thus selected the other less important minerals are arranged in groups or families. It is evident that no precise definition of these families can be given, as the connection is one of resemblance in many points, not of identity in any single character. In other words, it is a classification rather according to types than from definitions, as every true natural classification must be. The same cause, however, leaves the extent of the families somewhat undefined, and also permits considerable license in the arrangement of species. But both circumstances are rather of advantage in the present state of the science, as allowing more freedom in the grouping of species than could be obtained in a more rigid system of classification.

In collecting the families into orders, the guidance of chemistry is followed rather than of natural history, though the latter is also taken into consideration. Chemical names are assigned to the orders, but still regarded as names derived from the prevailing chemical characters, and not as definitions. Hence it must not be considered an error should two or three mineral species be found in an order with whose name, viewed as a definition, they may not agree.

Guided by these, and similar considerations, minerals may be divided into the following orders and families:

**Order I.—The Oxidized Stones.**

Families: 1. Quartz. 2. Feldspar. 3. Scapolite. 4. Haloid stones. 5. Leucite. 6. Zeolite. 7. Mica.

8. Serpentine. 9. Hornblende. 10. Clays. 11. Garnet. 12. Gems. 13. Metallic stones.

**Order II.—Saline Stones.**

Families: 1. Calc spar. 2. Fluor spar. 3. Heavy spar.

4. Gypsum. 5. Rock salt.

**Order III.—Saline Ores.**

Families: 1. Sparry iron ores. 2. Iron salts.

3. Copper salts. 4. Lead salts.

In describing the species we have followed this general plan. First, that name which it seems most expedient to adopt is given, with the principal synonyms, followed in the same line by the probable chemical formula. In these, silica is commonly assumed as Si; but we have given also the formula with Si for the more important species. In the descriptions the system of crystallization is noted, and the mineral more precisely characterized, by enumerating some of its more common forms and combinations with their characteristic angles. The physical characters of the species, its state of aggregation, cleavage, fracture, hardness (H.), and specific gravity (G.), follow; then its lustre, pellucidity, colour, and any other marked peculiarities. Next come its chemical characters, or its conduct before the blowpipe (B.B.), and the effect of acids, specially the hydrochloric (h.), nitric (n.), and sulphuric (s.). The chemical composition, or the amount of the different elements in 100 parts, generally deduced from the formula, but with notices of the more important variations indicated by the best analyses either from the substitution of isomorphous elements or other substances, are then noted. The principal localities where each species occurs, especially in our own country, with certain miscellaneous particulars, conclude the description.

We have also given similar characters of the orders and families, so far as this was possible. These, of course, apply chiefly to the more important and better marked or typical species (indicated by one or two asterisks [*] or **) prefixed to the name), but in many points are also descriptive of the others. The possibility of forming such general characters is the best proof that the groups are so far natural, and that the object of a scientific classification has been partially at least attained.

**PART II.—DESCRIPTION OF MINERAL SPECIES.**

**Order I.—The Oxidized Stones.**

The minerals contained in this order are either simple oxides, or compounds of oxides. Oxides of the true metals are not abundant, and occur generally as isomorphous with, or replacing, the earths and alkalies which compose the greater number. They have all a stony character, non-metallic lustre and colours, and are often white and more or less translucent, except the family of the Metallic Stones, which forms a transition group to the following order.

**Family I.—Quartz.**

Contains only one true species, and hence no general characteristic. Quartz is the true type or representative of the mineral kingdom.

**I.—Quartz.—Si, or Si.**

Hexagonal; the purest varieties tetartohedral. The primary pyramid P has the middle edge = 103° 34', and the polar edges = 135° 44', and is often perfect. Very frequently it appears as a rhombohedron R (or 4 P), with polar edges = 94° 15'. Crystals often of αP. P; αP. P. 4P, the forms αP and 4P being combined in an oscillatory manner, producing striæ on the face of the prism; αP. P. 4(2P 2) (fig. 101), the last face appearing as a rhomb replacing the angles between the two other forms. They are prismatic, or pyramidal, or rhombohedric when P is divided into R and −R; the latter very often wanting. Twins or macles common, with parallel axes, and either merely in juxtaposition (see fig. 80), or interpenetrating. The crystals occur either single, attached, or imbedded, or in groups and druses. Most frequently granular, massive, fibrous, or columnar; also in pseudomorphs, petrifications, and other forms. Cleavage, rhombohedric along R very imperfect; prismatic along $aP$ still more imperfect. Fracture conchoidal, uneven, or splintery. $H = 7$; $G = 2.5$–2.8; or 2.65 in the purest varieties. Colourless, but more often white, gray, yellow, brown, red, blue, green, or even black. Lustre vitreous, inclining to resinous; transparent or translucent, sometimes almost opaque. B.B. infusible alone; with soda effervesces and melts into a clear glass; insoluble in acids, except the fluorine; when pulverized, slightly soluble in solution of potash. Chem. com. 48% silicon and 51-96 oxygen, but frequently a small amount of the oxides of iron or titanium, of lime, alumina, and other substances.

Varieties are—Rock-crystal, highly transparent and colourless; Dauphiné, Switzerland, Tyrol, Hungary, Madagascar, and Ceylon. Amethyst, violet-blue (from iron peroxide or manganese), and often marked by zig-zag or undulating lines, and the colour disposed in clouds; Siberia, Persia, India, Ceylon, Brazil (white or yellow named topaz); Hungary, Siebenburg, Ireland, near Cork, and Aberdeen-shire. Wine yellow, or citrin and gold topaz; the brown or smoky quartz; and the black or morion; Siberia, Bohemia, Pennsylvania, and other places. Cairngorm stone, brown or yellow; Aberdeenshire mountains. The above are valued as ornamental stones; less so—

Rose-quartz, red inclining to violet-blue; Ben Macdhui, and Rabenstein in Bavaria. Milk-quartz, milk-white and slightly opalescent; Greenland. Prase, leek, and other shades of green; Saxony and Cedar Mountain in South Africa. Cats-eye, greenish-white or gray, olive-green, red, brown, or yellow; Ceylon and Malabar. Acanthite, yellow, red, or brown; India, Spain, and Scotland. Siderite, indigo or Berlin blue; Golling in Salzburg.

Common quartz, crystallized or massive, white or gray, also red, brown, &c., is a frequent constituent in many rocks. Some varieties are so impure as to be properly rocks, as—

(1.) Ferruginous quartz; or iron-flint, red, yellow, or brown, often associated with iron ores.

(2.) Jasper, red, yellow, or brown, but also green, gray, white, and black alone, or in spots, veins, and bands (Ribbon or Egyptian jasper); the Ural, Tuscan Apennines, the Harz, and many parts of Scotland.

(3.) Lydian stone, or flinty slate, black, gray, or white; has a splintery or conchoidal fracture, breaks into irregular fragments, and passes by many transitions into clay slate, of which it is often merely an altered portion, as in Scotland; used as a touchstone for gold, and at Eldal manufactured into ornaments.

(4.) Hornstone or chert, compact, conchoidal splintery fracture; translucent on the edges, and dirty gray, red, yellow, green, or brown; passes into flint, flinty slate, or common quartz; common in the mountain limestone, oolite, and greensand formations; and often contains petrifications, as shells, madreporites, and wood.

Other siliceous minerals seem intermediate between quartz and opal, as—Flint, grayish-white, gray, or grayish-black, also yellow, red, or brown; sometimes in clouds, spots, or stripes; semitransparent; lustre dull; fracture flat conchoidal; occurs chiefly in the chalk formation of England, North Ireland, Aberdeenshire, France, Germany, and other countries; sometimes in beds or vertical veins, oftener in irregular lumps or concretions, inclosing petrifications, as sponges, echinites, shells, or siliceous infusiona. The colour is partly derived from carbon or organic matter. It is used for gun-flints, and for the manufacture of glass and pottery, and cut into cameos or other ornaments.

Calcedony, semitransparent or translucent; white, gray, blue, green, yellow, or brown; stalactitic, reniform, or botryoidal, and in pseudomorphs or petrifications; Trevascus mine in Cornwall, Scotland, Hungary, Tyrol, Bohemia, Oberstein. Carnelian, chiefly blood-red, but also yellow, brown, or almost black; India, Arabia, Surinam, and Siberia; also Bohemia, Saxony, and Scotland (Perthshire). Plasma, leek or grass-green, and waxy lustre; Olympus, Schwarzwald, India, and China. Chrysoprase, apple-green; Silesia, and Vermont in North America. Heliotrope or bloodstone, dark-green, sprinkled with deep-red spots; Siberia, Bohemia, the Fassa Valley, the Island of Rum and other parts of Scotland. Agates, mixtures chiefly of calcedony in layers, with jasper, amethyst, or common quartz, abound in the amygdaloids of our own and other countries. Onyx, alternate layers of white, brown, or black, was much used in ancient times for cameos.

Some crystals are remarkable for their great size, as one in the Museum at Paris, measuring 3 feet in diameter, and weighing nearly 8 cwt. Other specimens contain cavities inclosing various substances, more than 24 known, as silver, iron pyrites, rutile, magnetite, tremolite, amianthus, mica, tourmaline, topaz; also air, water, naphtha, or other fluids.

#2. Opal.—Si, H.

Amorphous; fracture conchoidal; very brittle. $H = 5$–6.5; $G = 2.1$–2.2. Transparent to opaque; vitreous, inclining to resinous. Colourless, but often white, yellow, red, brown, green, or gray, with a beautiful play of colours. B.B. decrepitates and becomes opaque, but is infusible; in the closed tube yields water; almost wholly soluble in solution of potash. Chem. com., silica, with 5 to 13 per cent. water; or probably a mere hardened natural gelatine of silica with water as an accidental mixture.

Varieties are—(1.) Hyalite, glassy-opal, or Muller's glass, transparent, colourless, very glassy; small botryoidal or incrusted; Frankfort on the Maine, Kaisersuhl in the Breisgau, Schemnitz in Hungary, in Silesia, Moravia, Mexico, and other places. (2.) Fire-opal or girasol, transparent, brilliant vitreous lustre; bright hyacinth red or yellow; Zimapan in Mexico, and the Faroe Islands. (3.) Noble opal, semitransparent or translucent; resinous inclining to vitreous; bluish or yellowish-white, with brilliant prismatic colours; in irregular masses or veins at Czernowitz near Eperies in Hungary, Frankfort, and Gracios a Dics in Honduras. (4.) Common opal, semitransparent, vitreous; white, yellow, green, red, or brown; Hungary, also Faroe, Iceland, the Giant's Causeway, and the Western Isles of Scotland. (5.) Semi-opal, duller and less pellucid. Wood-opal or lithozoyth, with the form and texture of wood distinctly seen; Hungary, also Bohemia, and near Hobart's Town in Tasmania. (6.) Menilite, compact, reniform; opaque and brown or bluish-gray; Mont Menil near Paris. (7.) Opal jasper, blood-red, brown, or yellow. (8.) Cacholong, opaque, dull, glimmering, or pearly, and yellowish or rarely reddish-white; in veins or reniform and incrusting; Faroe, Iceland, the Giant's Causeway, and in Buchara. One variety is named Hydroplane, from imbibing water and becoming translucent. (9.) Siliceous sinter, deposited from the Geyser and other hot springs near volcanoes; and Pearl sinter, incrusting volcanic tufa at Santa Flora in Tuscany (Fiorti), in Italy, and in Auvergne. That from the Geyser contains 84% silica, 3% alumina, 1% peroxide of iron, 1% magnesia, 0.7 lime, 0.9 potash and soda, and 7.9 water.

2 b. Earthly Silica.—(a) Spongiform quartz, coarse earthy, soft and often friable, and yellow or grayish-white; porous, and swims on water till saturated; St Ouen near Paris. (b) Tripoli, coarse or fine earthy; white, gray, or yellow; near Tripoli in Africa, Corfu, Bohemia, Saxony, and Bavaria. (c) Polishing slate (Polirschiefer), white or yellow; slaty texture, opaque, brittle, and swims on water; at Bilin in Bohemia; consists of the siliceous remains of animals or plants (Diatomaceae). (d) Adhesive slate, from Montmartre near Paris; and (e) Mountain meal, snow-white, pearly, gray, or greenish; have a similar origin; Santa Fiora in Tuscany, Oberohle in Hanover, Kymmenegard in Sweden (where used as food), in Bohemia, and the Isle of France.

**Family II.—Felspar.**

Crystallization monoclinohedric or triclinohedric, both very similar in aspect and angles. Cleavage very distinct, especially the basal \( P \); less so the clino- or brachy-diagonal \( M \). \( G = 24 \ldots 32 \), but mostly \( 25 \ldots 28 \); \( H = 6 \), or a little more. Slightly or not at all soluble in acids. B.B. fusible, but often with difficulty. Translucent, pure varieties highly transparent. Colourless, white, or shades of red; less common, green or yellow. Chem. com. anhydrous silicates of alumina, and of an alkali or lime.

The felspars are very important constituents of the earth's crust, occurring in nearly all the igneous rocks, and in many of the stratified crystalline schists. In true strata, they are found chiefly as fragments or decomposed, and in the latter state form a large part of most soils and clays. In the older mineralogists' popular language many species are conjoined under the common name of felspar, which are now considered as distinct, each of them having not only its peculiar physical and chemical characters, but also geognostic position and associated group of minerals. Thus orthoclase, and the other more siliceous felspars with potash, abound in granite and the plutonic rocks; the less siliceous, with soda and lime, characterize the volcanic rocks—as labradorite the basaltic group, glassy felspar the trachytic. Orthoclase occurs with quartz, hornblende, and mica; glassy felspar only with hornblende and mica, or only with augite; labradorite only with augite, rarely if ever with quartz or hornblende.

The felspars are best known from similar minerals by their hardness (scarce scratch with a good knife), difficult fusibility, and unequal cleavages. The following marks may aid the student in distinguishing the more common species. If the basal cleavage plane is turned to the spectator, then in orthoclase it forms a right angle with the clinodiagonal cleavage planes \( M \) on both hands; in albite, oligoclase, and petalite it forms an obtuse angle with \( M \) on his right hand; and in labradorite and anorthite on his left hand. Orthoclase, albite, andesine, and oligoclase are insoluble in acids; ryacolite, labradorite, and anorthite more or less soluble.

S. von Waltershausen states that the felspars form a series with the oxygen of the silica, alumina, and \( R = x : 3 : 1 \), in which \( x \) ranges from 24 to 4. Baulite (with 80 silica), albite (69 silica), and anorthite (44 silica), being the three true species, of which the others are mixtures, according to a peculiar law (isomorphism of groups).

**3. Orthoclase.**—\( Al_2Si_3O_8 + K_2SiO_3 \) or \( Al_2Si_3O_8 + K_2SiO_3 \). Monoclinohedric; \( C = 65^\circ 47', \alpha P = 118^\circ 50', \beta P = 65^\circ 53', (2P) \( 90^\circ \), \( 2P = 35^\circ 12' \). Crystals often of \( \alpha P \). \( OP \) \( P \); or (\( \alpha P \)) \( M \). \( \alpha P \) (\( T \); \( l \)) \( OP \) (\( P \)). \( 2P = 90^\circ \) (fig. 102), are short rhombic prisms, when \( \alpha P \) predominates; or tabular when (\( \alpha P \)); or short hexagonal prismatic when \( \alpha P \) and (\( \alpha P \)); or rectangular prismatic when \( OP \) and (\( \alpha P \)) predominate; and occur single, attached, or in druses. Macles are frequent, especially with the twin axis parallel to the chief axis, and often partially interpenetrating as in fig. 103; also massive and coarse or fine granular. Cleavage, basal (\( P \)) very perfect; clinodiagonal (\( M \)) perfect (\( P \) to \( M = 90^\circ \)); and hemiprismatic \( \alpha P \) in traces. Fracture conchoidal or uneven and splintery. \( H = 6 \); \( G = 253 \ldots 258 \). Transparent to translucent on the edges; vitreous, but often pearly on the more perfect cleavage; and also opalescent, with bluish or changing colours. Colourless, but generally red, yellow, gray, or green. B.B. fuses with difficulty to an opaque vesicular glass; not affected by acids. Chem. com. 65% silica, 18 alumina, and 16% potash, but generally 10 to 14 potash, 1 to 4 soda, 0 to 1% lime, 0 to 2 iron peroxide.

Varieties are—(1.) Adularia and Ice-spar, transparent or translucent, splendid, and almost or wholly colourless. Some with a bluish opalescence are named Moonstone; St Gotthardt, Mont Blanc, Dauphine, Arendal, Southern Norway, Greenland, and Ceylon.

(2.) Common felspar, less splendid and transparent, and generally white or red, especially flesh-red, is a very common constituent of many rocks. Crystals at Baveno on Lago Maggiore, Lomnitz in Silesia, Mourne Mountains and Wicklow in Ireland, Aberdeenshire (at Rubislaw, 4 or 5 inches long) in Scotland, and at Carlsbad and Elbogen in Bohemia. Amazon stone, verdigris-green, from Lake Ilmen; and Murchisonite, golden or grayish-yellow, from Arran and Dawlish, seem varieties.

(3.) The Glassy felspar or sanadine (\( C = 63^\circ 55', \alpha P = 119^\circ 13' \)), contains 3 to 12 potash, 3 to 10 soda, 0 to 3 lime, and 0 to 2 magnesia. Crystals imbedded, yellowish-white or gray; vitreous; transparent or translucent, and often much cracked;

Drachenfels on the Rhine, Mont d'Or and other parts of Auvergne, Hungary, Italy, Iceland, Mexico, Chili, and other countries; also in Arran, Rum, and other parts of Scotland. Ryacolite, from Vesuvius and Lake Laach, is only a variety—the specimen analysed, having been impure. Loxoclase, from Hammond, New York, also a variety with much soda. Baudite and Krablite from Iceland, probably mixtures with quartz.

Orthoclase occurs in granite, gneiss, and porphyry in many countries. It is commonly associated with quartz, sometimes, as in the graphic granite of Portsoy and Aberdeenshire, in regular combinations. It is very liable to decomposition, when it is converted especially into kaolin, used for manufacturing porcelain and stoneware. The adularia or moonstone, and the green amazon stone are cut as ornamental stones.

Compact felspar, or feldstein, a mixture of orthoclase and quartz, often harder than the pure mineral. \( G = 259 \ldots 3 \). White, gray, red, or yellow, sometimes in spots or bands. The softer varieties, or claystones, often bluish or purplish. \( G = 221 \). B.B. most melt with difficulty to a white enamel (hornstone is infusible). Common in the porphyry rocks of many countries, as in Scotland (Cheviots, **4. Albite.** \( \text{Al}_2\text{Si}_3 + \text{Na}_2\text{Si} \) or \( \text{Al}_2\text{Si}_3 + \text{Na}_2\text{Si} \).

Triclinohedric; \( OP (P) = \infty P \approx (M) = 86^\circ 24', \infty P' (l) = 122^\circ 15' \). Crystals, generally like those of orthoclase, are tabular or prismatic (fig. 105). Maces very common, especially united by a face of \( \infty P \approx \) (fig. 106), the re-entering angle between the faces of \( OP (P \) and \( P' = 172^\circ 48' \)) being very characteristic. Fig. 107 is another mace common in periclase. Also massive and foliated or radiating. Cleavage, basal and brachydioagonal almost equally perfect, prismatic along \( \infty P \) imperfect; fracture conchoidal or uneven. \( H. = 6...65; G. = 2.6...2.67 \). Rarely transparent, usually translucent or only on the edges; vitreous, inclining to pearly on the cleavage. Colourless, but generally white, gray, green, red, or yellow; streak white. B.B. difficultly fusible, tinging the flame yellow, to a white semi-opaque glass; not affected by acids. Chem. com. 69-3 silica, 19-1 alumina with 0.1 to 1 iron peroxide and 11-6 soda with 0.3 to 4 lime, 0 to 2-5 potash, and 0 to 0.5 magnesia. Hence albite and orthoclase both contain soda and potash, only in different proportions. Albite is best marked by the frequent re-entering angles, its more easy fusibility, and the obliquity (93° 35') of its cleavage planes. *Periclase*, with \( G. = 2.54...2.6 \), and slight diversity in angles, is only a variety.

Albite is a constituent of many greenstones (Edinburgh), of granite (Aberdeenshire), syenite, gneiss, porphyry, and trachyte; also in beds and veins; crystals at Barèges in the Pyrenees, Bourg d'Oisans in Dauphiné, St Gotthard, the Tyrol, Salzburg, and Arendal. *Adinole* is a compact gray or red mixture of albite and quartz.

**5. Andesine.** \( \text{Al}_2\text{Si}_3 + (\text{Na}, \text{Ca})_2\text{Si} \).

Triclinohedric; crystals and physical properties similar to albite, but the cleavage less distinct. \( G. = 2.67...2.73 \). B.B. more easily fusible (like oligoclase) to a milky somewhat porous glass. Chem. com. 60 silica, 23 alumina, 7 soda, 6 lime, 1 potash, and 1 magnesia. Cordilleras, in andesite or diorite porphyry; Vosges Mountains, near Dresden, and Iceland.

*Saccorhile*, compact, or fine granular; white or apple-green; Frankenstein, Silicia, and Canada; seems a variety.

**6. Labradorite.** \( \text{Al}_2\text{Si}_3 + (\text{Ca}, \text{Na})_2\text{Si} \), or \( \text{Al}_2\text{Si}_3 + \text{R}_2\text{Si} \).

Triclinohedric; \( OP : \infty P \approx = 86^\circ 25'; OP' : \infty P' = 114^\circ 26' \). Crystals rare; mostly massive and granular; maces like those of periclase (fig. 107). Cleavage basal, very perfect; brachydioagonal less so; both usually striated. \( H. = 6; G. = 2.68...2.74 \). Translucent, or only on the edges; vitreous, on the cleavage pearly or resinous. Gray, passing into white, green, yellow, or red. The faces of \( \infty P \approx \) often exhibit very beautiful changing colours,—blue, green, yellow, red, or brown,—sometimes in bands intersecting at certain angles. B.B. fuses more readily than orthoclase to a compact colourless glass; soluble when pulverized in n. acid. Chem. com. 53-7 silica, 29-7 alumina with 1 to 2 iron peroxide, 12-1 lime, and 4-5 soda with 0.3 to 2 potash, 0.1 to 2 magnesia, and 1 to 3 water—the latter probably not essential.

Common constituent of dolerite, greenstone, the gabbro, and hypersthene rocks. Labrador, Finland, Harz, Meissner, Tyrol, Mourne Mountains, Campsie and Milngavie near Glasgow, and Skye; also Etna and Vesuvius, and in meteoric stones.

*Scolezerose*, from Pargas, is a pure lime-labradorite.

*Glaucolite*, from Lake Baikal, pale blue or greenish, with traces of cleavage in two directions, and \( G. = 2.72...3.2 \), is not distinct. *Sauveterre*, compact, dull, subtranslucent; gray, inclining to blue, green, or red; B.B. fuses to a gray or greenish-white enamel, and is not acted on by acids; is merely an impure labradorite. Alps near Geneva, Harz, Styria, Apennines, and Corsica.

**7. Couzermanite.** \( 2 \text{Al}_2\text{Si}_3 + 3(\text{Ca}, \text{K}, \text{Na}, \text{Mg})_2\text{Si} \).

Monoclinohedric; \( C = 87^\circ; \infty P = 96^\circ \). Cleavage clinodioagonal. \( H. = 6; G. = 2.69 \). Opaque, vitreous, or resinous. Pitch-black, blackish-blue, or gray. B.B. melts to a white enamel; not affected by acids. Chem. com. by Dufresnoy's analysis, 52-37 silica, 24-02 alumina, 11-85 lime, 1-40 magnesia, 5-52 potash, and 3-96 soda. Couzernas in the Pyrenees.

**8. Anorthite, Christianite.** \( \text{Al}_2\text{Si}_3 + \text{Ca}_2\text{Si} \), or \( 3 \text{Al}_2\text{Si}_3 + \text{R}_2\text{Si} \).

Triclinohedric; \( OP : \infty P \approx = 85^\circ 48'; \infty P' : \infty P = 120^\circ 30' \). Crystals and maces like albite, with angle between \( P \) and \( P' = 188^\circ 24' \). Cleavage, basal and brachydioagonal perfect. \( H. = 6; G. = 2.7...2.76 \). Transparent or translucent; vitreous. Colourless or white. B.B. fuses to a clear glass; soluble without gelatinizing in conc. h. acid. Chem. com. 43-9 silica, 36-3 alumina, and 19-8 lime with 1 to 5 magnesia, 0.3 to 8 soda, 0.2 to 1 potash, and 0.1 to 2 iron peroxide. Monte Somma, Iceland, Java.

*Amphodelite* has the same composition and a close resemblance in crystalline forms, cleavage, and maces; is reddish-gray, or dirty peach-blossom red. Lojo in Finland, and Tunaberg in Sweden. *Indianite* from the Carpathian; gelatinizes with acids; and B.B. is infusible.

**9. Oligoclase.** \( 2 \text{Al}_2\text{Si}_3 + \text{Na}_2\text{Si} \), or \( \text{Al}_2\text{Si}_3 + \text{Na}_2\text{Si} \).

Triclinohedric; \( OP : \infty P \approx = 86^\circ 45'; \infty P' : \infty P \) about 120°. Crystals rather rare, and maces resemble albite. Cleavage, basal perfect; brachydioagonal less perfect; \( \infty P' \) imperfect. \( H. = 6; G. = 2.64...2.68 \). More or less translucent; vitreous, pearly or resinous on the cleavage. White, with a tinge of green, gray, or red. B.B. melts easier than orthoclase or albite to a clear glass; not affected by acids. Chem. com. 68 silica, 23 alumina, and 14 soda; but 20 to 24 alumina, 7 to 12 soda, 1 to 4 potash, 5 to 4 lime, 0 to 1 magnesia, and 0 to 4 iron peroxide, Scotland, Scandinavia, Ural, Harz, and Morea. The *Sunstone* or *Aventurine felspar* from Tvedestrand, Norway, Lake Baikal, and Ceylon, with a fine play of colour, belongs to this species. *Hofnafeldite*, in lava, Hafnelford, Iceland; \( G. = 2.729 \); is a lime-oligoclase.

**10. Latrobeite.**

*Diploite.* \( 4 \text{Al}(\text{Mn})_2\text{Si} + 3(\text{Ca}, \text{Mg}, \text{K})_2\text{Si} \).

Triclinohedric; crystals indistinct, prismatic; mostly massive. Cleavage in three directions, intersecting at 91°, 93° 30', and 98° 30'; fracture uneven. H. = 5 to 6; G = 2-7. Translucent; vitreous. Rose-red to reddish-white. B.B. becomes white, intumesces, and melts on the edges to a porous mass. Amitok Island in Labrador, and Bolton in Massachusetts.

11. PETALITE.—4 Al Si₄ + 3 (Li, Na) Si₄.

Probably mono- or triclinohedric, but only coarse granular. Cleavage in one direction distinct, in a second less so, and mere traces of a third. H. = 6-5; G. = 2-4...2-5. Greenish, grayish, or reddish white, to pale red. Translucent; vitreous or pearly. B.B. melts easily into an obscure porous glass, colouring the flame red; not affected by acids. Chem. com. 77% silica, 18% alumina, 3% lithia, and 3% soda. Uteo, Bolton in Massachusetts, and York in Canada.

12. STROUMENNE, Triphane. {4 Al Si₄ + 3 (Li, Na, K) Si₄, or

Monoclinohedric; C. = 60° 40' P = 87°; isomorphous with augite (diopside). Cleavage, prismatic ∥ P perfect; orthodiagonal more perfect, chiefly massive or foliated. H. = 6-5...7; G. = 3-1...3-2. Translucent; vitreous or pearly. Pale greenish-gray or white to apple-green; streak white. B.B. intumesces slightly, tinged the flame momentarily purplish-red, and fuses easily to a colourless glass; not affected by acids. Chem. com. 65% silica, 28% alumina, and 6% lithia, with 0-1 to 2% soda, 0 to 4% potash, and 0 to 1 lime. Uteo in Sweden, Sterzing and Lisens in the Tyrol, Killiney near Dublin, Peterhead in Scotland, and crystals at Norwich in Massachusetts.

KILLINITE.—Crystalline foliated. Cleavage along a prism of 135°. H. = 4; G. = 2-65. Greenish-gray, yellow or brownish-green. B.B. melts difficultly to a white porous enamel. Chem. com. 2 Al Si₄ + R Si₄ + 3 H₂O, being potash, lime, magnesia, iron protoxide, and lithia. Killiney near Dublin, with spodumene.

13. KASTOR.—2 Al Si₄ + Li Si₄.

Monoclinohedric. Cleavage distinct in two directions, meeting at 141°. H. = 6...6-5; G. = 2-38...2-40. Transparent; splendid vitreous. Colourless. B.B. melts difficultly to a transparent colourless bead, tinged the flame deep carmine-red; not soluble in n. acid. Chem. com. 78% silica, 18% alumina, and 2% lithia. Elba. Probably a variety of petalite.

14. POLLUX.—Al Si₄ + K Si₄ + Na Si₄ + H₂O (?).

Massive. Traces of cleavage; fracture conchoidal. H. = 6...6-5; G. = 2-87...2-89. Transparent; splendid vitreous. Colourless; optically biaxial. B.B. melts on thin edges to an enamel-like porous glass, colouring the flame reddish-yellow. Elba, with castor. Both much resemble quartz.

15. ZYGADITE.—Si₄ Al₄ Li₄.

Triclinohedric, in macle like albite. H. = 5-5; G. = 2-51. Subtranslucent; vitreous. Reddish or yellowish white. Andreasberg.

16. AMORPHOUS FELSPAR.

Mineral substances, with no regular structure, and rather rocks than minerals.

(a) OBSIDIAN.—Compact in globular grains or masses. Fracture conchoidal; brittle. H. = 6...7; G. = 2-2...2-4. Semitransparent to translucent on the edges; vitreous. Black, gray, green, red, and brown, or striped and spotted. B.B. melts to a foamy mass, a glass or enamel. Chem. com. indeterminate, but 70 to 80 silica, 6 to 12 alumina, 3 to 10 sodas, 3 to 6 potash, 1 to 7 lime, 1 to 2 magnesia, and 1 to 6 iron peroxide. Streams or detached masses near volcanoes, as Iceland, Lipari Islands, Milo, Santorin, Teneriffa, Mexico, and Hungary.

(b) PUMICE.—Porous, vesicular, or fibrous. Fracture conchoidal or flat; very brittle. White, gray, yellow, brown, or black. H. = 5; G. in powder—2-19...2-2; in masses swarms on water. B.B. melts more or less easily to a white enamel. Chem. com. like obsidian, of which it seems a peculiar state. Andernach on the Rhine, Lipari, and Ponza Islands. Used as a polishing material.

(c) PEARLSTONE.—Roundish concentric globules imbedded in a vesicular basis. Fracture conchoidal; very brittle. H. = 6; G. = 2-2...2-4. Pearly. Reddish, bluish, or ash-gray; also yellow, red, or brown in stripes or spots. B.B. melts to a white fungus-like mass. Chem. com. indefinite, or a mixture of felspar and opal, with 2 to 4 per cent. water. Hungary, Siberia, Mexico. Sphaerulite, small spherical concretions in pearlstone in Hungary and Mexico, and in pitchstone in Arran and Meissen.

(d) PITCHSTONE.—Compact, slaty, or in concentric scaly concretions. Fracture conchoidal; splintery. H. = 5-5...6; G. = 2-2...2-3. Subtranslucent to opaque; resinous. Gray, green, yellow, red, brown, black. B.B. melts to a porous glass or gray enamel. Chem. com. indefinite; but 64 to 76 silica, 11 to 14 alumina, 1 to 3 lime, 1 to 6 soda, 0 to 6 potash, 0 to 7 magnesia, 1 to 4 iron peroxide, and 5 to 9 water. Beds or veins at Tokai, Kremsnitz, Scheinitz in Hungary, Meissen, Saxony, Newry in Ireland, and Arran in Scotland (the latter said to contain 2 per cent. of bitumen).

FAMILY III.—SCAPOLITE.

Crystallization tetragonal or hexagonal (prehnite rhomboic). Cleavage more or less perfect. H. = 5...6, or a little more in prehnite; G. = 2-6...3. All fusible and soluble in acids, and gelatinize. Chem. com. anhydrous silicates of alkalies or lime, and of alumina. They are generally transparent or translucent. Colourless, but often with green or yellow tinge and resinous lustre. They occur chiefly in volcanic or in plutonic rocks.

17. SCAPOLITE, Wernerite. {Al₂ Si₄ + 3 (Ca, Na) Si₄, or

Tetragonal; P 63° 32'. Crystals ∥ P, ⊥ P, ⊥ P, often long prismatic; also massive and granular or columnar. Cleavage, ∥ P ⊥ rather perfect, ⊥ P less perfect. H. = 5...5-5; G. = 2-6...2-8. Transparent or translucent; vitreous, pearly, or resinous. Colourless, but pale gray, green, yellow, or red. B.B. melts with effervescence to a vesicular glass; in the closed tube many show traces of fluorine; with solution of cobalt become blue; soluble in h. acid. Chem. com. 49% silica, 27% alumina (with 0 to 3% iron peroxide), 22% lime and soda (but 12 to 21 lime, 1 to 7 soda, 0 to 2 magnesia, and 1 to 3 potash). Analyses differ widely, and some resemble the anorthite, others the labradorite felspars. Arendal, Tunaberg, Pargas, Bolton in Massachusetts, and Governor in New York. Easily known by its distinct rectangular cleavage, the resinous lustre on fracture surfaces, and its action before blowpipe.

18. MEONITE.—Al₂ Si₄ + 3 Ca₂ Si₄.

Tetragonal; P 63° 48'. Crystals, ∥ P ⊥ P, ⊥ P, prismatic. Cleavage, ∥ P ⊥ perfect, ⊥ P imperfect. Fracture conchoidal, H. = 5...6; G. = 2-6...2-7. Translucent and transparent; vitreous. Colourless or white. B.B. fuses with much intumescence to a vesicular glass; soluble in h. acid without gelatinizing. Chem. com. 42-5% silica, 31-5% alumina, and 26 lime (but 21 to 24 lime, 0-5 to 2 soda, 0-3 to 1 potash, and 0 to 1 magnesia.) Somma, Vesuvius.

19. The following are varieties of, or closely related to scapolite:

Nuttelite.—Tetragonal; P 64° 40'; forms and cleavage like scapolite. H. = 5-5; G. = 2-74...2-75. Vitreous; on fracture resinous. Ash or greenish gray. B.B. like scapolite. Bolton in Massachusetts.

Barrowite.—Granular or compact, with one distinct cleavage. Translucent on the edges; pearly. Snow-white. Mineralogy.

Gelatinizes in warm h. acid. Chem. com. about 49 silica, 34 alumina, 5-6 lime, and 1-5 magnesia. Barsowaskoi in Ural. Bytownite, translucent; vitreous; light greenish-blue, Bytown in Upper Canada; is similar.

20. Palagonite. \((\text{Al}, \text{Fe})_3 \text{Si} + 3 (\text{Ca}, \text{Mg}, \text{Na}) \text{Si}\) \(+ 9 \text{H}\).

Amorphous; fracture conchoidal. H. nearly 5; G = 2-4. Transparent or translucent; resinous to vitreous. Wine-yellow to yellowish-brown. B.B. fuses readily to a shining magnetic bead. Easily soluble in acid. Palagonia in Sicily, Iceland, Galapagos, Nassau, and Cassel. Rather a rock.

21. Diopside. \(-\text{Al} \text{Si} + 4 (\text{Ca}, \text{Na}) \text{Si}\).

Tetragonal, in rounded eight-sided prisms. Cleavage, \(x\) P and \(x\) P \(z\). Scratches glass. G = 2-646. Vitreous. Whitish or reddish. B.B. becomes opaque, and melts readily to a white vesicular glass. Slightly affected by acids. Chem. com. 55-7 silica, 25-1 alumina, 9-1 lime, and 10-1 soda. Mauléon, and Castillon in the Pyrenees.

22. Nepheline, Elacolite. \((\text{Al}, \text{Si})_4 + 4 (\text{Na}, \text{K}) \text{Si}\), or \(\text{Al} \text{Si} + \text{R}^2 \text{Si}\).

Hexagonal; P 88° 6. Crystals, \(x\) P, \(x\) P, \(x\) P, \(x\) P, \(x\) P, imbedded, or in druses; also massive granular. Cleavage, basal and \(x\) P imperfect. Fracture conchoidal or uneven. H. = 5-5...6; G. = 2-68...2-64. Transparent or translucent; vitreous. Colourless or white (nepheline); or more opaque, dull resinous, and green, red, or brown (elacolite). B.B. melts difficulty (nepheline), or easily with slight effervescence (elacolite), into a vesicular glass. Soluble and gelatinizes in h. acid. Chem. com. 44-84 silica, 23-04 alumina, 16-05 soda, 6-07 potash, with 0-2 to 2 lime, and 0-5 to 1-5 iron peroxide. Nepheline at Monte Somma, Capo di Bove, Katzenbuckel in the Odenwald, Aussig, and the Lansitz. Elacolite in the zircon syenite at Laurvig, Fredrikshamn, Brevig, and Miask.

Davinci, \(P 51° 46'\); long prismatic. G. = 2-43. Contains a little chlorine and carbonic acid. Vesuvius and Somma.

23. Cancrinite. \(-\text{Al} \text{Si} + 4 \text{Na} \text{Si} + 2 \text{Ca} \text{C}\).

Hexagonal; massive and columnar. Cleavage, prismatic \(x\) P perfect. H. = 5...5-5; G. = 2-42...2-46. Translucent or transparent; resinous, vitreous, or pearly on cleavage. Green, yellow, and rose-red. B.B. melts to a white vesicular glass. Soluble with effervescence in h. acid. Chem. com. one atom of a nepheline silicate with two atoms carbonate of lime = 39-3 silica, 29 alumina, 7-6 soda, and 14-1 carbonate of lime. Miask, and Litchfield in Maine; but in the latter the carbonate is Na C + Ca C. Stroganovite has the soda chiefly replaced by lime. Sládjanova River in Dauria.

24. Gehlenite. \((\text{Al}, \text{Fe})_3 \text{Si} + (\text{Ca}, \text{Mg}, \text{Fe}) \text{Si}\).

Tetragonal. Crystals, OP, \(x\) P, thick tabular or short prismatic. Cleavage, basal rather perfect, \(x\) P traces. H. = 5-5...6; G. = 2-9...3-1. Translucent on the edges; dull resinous. Mountain, leek, or olive green, to liver-brown. B.B. melts difficulty in thin fragments. Gelatinizes with h. acid. Chem. com. 31-4 silica, 20 to 24 alumina, 3 to 6 iron peroxide, 35 to 38 lime, 0 to 4 magnesia, 0 to 1-7 iron protoxide, and 1 to 3 water. Mount Monzoni in the Fassa Valley.

25. Humboldtnite. \((\text{Al}, \text{Fe})_3 \text{Si} + 2 (\text{Ca}, \text{Mg}, \text{Na}, \text{K}) \text{Si}\).

Tetragonal; P 66° 24'; OP, \(x\) P, tabular or short prismatic. Cleavage, basal perfect. H. = 5...5-5; G. = 2-91...2-95. Translucent on the edges; vitreous or resinous. Yellowish-white, honey-yellow, and yellowish-brown. B.B. melts easily to a light or blackish coloured glass. Gelatinizes with h. acid. Chem. com. about 40 silica, 32 lime, 6 to 7 magnesia, 2 to 4 soda, 0-3 to 1 potash, 6 to 11 alumina, and 4 to 10 iron peroxide. Vesuvius and Capo di Bove. Melilite, Somervellite, and Zurlite are identical. Sarkolite, from Vesuvius, is similar.

26. Prehnite, Koupbolite. \((\text{Al}, \text{Si})_2 + 2 \text{Ca} \text{Si} + \text{H}\), or \((\text{Al}, \text{Si})_2 + \text{Ca} \text{Si} + \text{H}\).

Rhombic, \(x\) P 99° 56', \(x\) P \(x\) 33° 0', \(x\) P \(x\) 126° 46'. Crystals \(x\) P, \(x\) P, or \(x\) P (m), \(x\) P (P), \(x\) P (O), \(x\) P (e) (fig. 108), tabular or short prismatic, in druses, fan-shaped or cock's-comb groups. Also granular or spherical, reniform and fibrous. Cleavage, basal rather perfect, \(x\) P imperfect. H. = 6...7; G. = 2-8...3. Semi-transparent or translucent on the edges; vitreous, on \(x\) P pearly. Colourless, but mostly greenish-white, olive, apple, or leek-green. When heated becomes polar-electric. B.B. melts easily, with much intumescence, to a porous enamel. Soluble in con. h. acid, but only gelatinizes perfectly when previously ignited or fused. Chem. com. 44-4 silica, 24-6 alumina, 26-7 lime, and 4-3 water (but with 0-1 to 7 peroxide of iron and manganese). Cape of Good Hope; Bourg d'Oisans in Dauphine; Ratschinges and Passa in Tyrol; Friskie Hall and Campsie, Dumbartonshire; Hartfield Moss, Renfrewshire; Corstorphine Hill, the Castle Rock, and Salisbury Craigs, near Edinburgh; Mull; Skye; and Dalnabo, near Glengairn, Aberdeenshire.

Prehnitoid, like prehnite, but scarce affected by h. acid. Wexio in Sweden.

27. Karpholite. \(-\text{Al} \text{Si} + \text{Mn} \text{Si} + 2 \text{H}\).

Rhombic; radiating or stellated and acicular. H. = 5...5-5; G. = 2-9...3. Translucent; silky. Straw to wax yellow. B.B. intumesces and forms an opaque brown glass, scarcely affected by acids. Chem. com. 37 silica, 30-6 alumina, 21-6 manganese protoxide, 10-8 water, with iron protoxide and fluoric acid. Schakenwald and Wippra in the Harz.

28. The following minerals may follow prehnite:

(a) Kirunomite.—Spheroidal; radiating fibrous. H. = 2; G. = 2-9. Opaque; dark olive-green. B.B. becomes black, and partially fuses. Chem. com. 40-5 silica, 11-4 alumina, 23-9 iron protoxide, 19-8 lime, and 4-4 water. Mourne Mountains, Ireland.

(b) Huronite.—Granular or foliated. H. = 3-25; G. = 2-86. Translucent; pearly or resinous. Pale yellowish-green. B.B. infusible, but greyish-white. Not affected by acids. Chem. com. 45-8 silica, 33-9 alumina, 4-3 iron protoxide, 8-1 lime, 1-7 magnesia, and 4-2 water. Lake Huron.

(c) Nerolite.—Fine columnar. H. = 4-25; G. = 2-47. Translucent or opaque. Greenish-yellow. B.B. infusible, but becomes snow-white and pulverulent. Chem. com. 73 silica, 17-4 alumina, 3-3 lime, 1-5 magnesia, and 4-3 water. Stamstead in Lower Canada.

Family IV.—Haloid Stones.

These minerals are so named from their resemblance to salts. Their crystallization is rhombic or monoclinohedric. H. = 4...6; G. = 2-3...3-1. Soluble in acids. Generally infusible, or with difficulty. Most colour the B.B. flame bluish-green from phosphoric acid, being compounds of this acid with alumina, in some also with magnesia or iron protoxide. Are brightly-coloured minerals, of blue, green, or yellow tints. Most contain water, and do not form constituents of rocks.

29. Lazulite, Azurite. \(-\text{Al} \text{P} + (\text{Mg}, \text{Fe})_3 \text{P} + 2 \text{H}\).

Monoclinohedric. C. = 88° 2', \(x\) P 91° 30', P 99° 40', \(P\) 100° 20', \(P\) \(x\) 30° 2'; crystals pyramidal, tabular or prismatic, but rare; usually massive or granular. Cleavage, prismatic \(x\) P imperfect; fracture uneven, splintery. H. = 5...6; G. = 3...3-1. Translucent on the edges; vitreous. Indigo, smalt, or other shades of blue inclining to green or white; streak white. In closed tube yields water and loses its colour. B.B. intumesces, but does not melt. With cobalt solution assumes a fine blue colour. Scarcely affected by acids till after ignition, when almost wholly soluble. Chem. com. 44-1 phosphoric acid, 31-7 alumina, 9 to 12 magnesia, 2 to 10 iron protoxide, 1 to 4 lime, and 5-7 water. Werfen in Salzburg, Vorau (Vorautite) and Krieglach in Styria, Tijuco in Brazil, and Lincoln county in North Carolina.

30. Calaite, Turquoise.—AP P + 5 H.

Reniform; stalactitic or incrusting. Fracture conchoidal. H. = 6; G. = 2-6...2-8. Opaque or translucent on the edges; dull or waxy. Sky-blue, greenish-blue, rarely green; streak greenish-white. In the closed tube yields water, decrepitates violently, and becomes black. B.B. infusible, but colours the flame green. Soluble in acids. Chem. com. 46-89 alumina, 32-57 phosphoric acid, and 20-54 water, but mixed with phosphate of iron and copper. Silesia, Lausitz, and Voigtländer. Oriental turquoise, in veins, at Meschid near Herat; in pebbles in Khorazan, Bucharia, and Syrian desert. Takes a fine polish, and is valued as an ornamental stone.

31. Fischerite.—AP P + 8 H.

Rhombic; ∞P 118° 32', mostly in crusts or indistinct six-sided prisms. H. = 5; G. = 2-46. Transparent; vitreous; green. Slightly soluble in h. or n., wholly in s. acid, and on heating becomes white or partly black. Chem. com. 42 alumina, 29 phosphoric acid, 29 water, with a little lime and copper oxide. Nischmal Taglask.

Pegmatite.—Probably rhombic, ∞P 127° nearly; in very small prismatic crystals or thin crusts. Emerald, grass-green, or white. H. = 3-5; G. = 2-49...2-54. Chem. com. like Fischerite, but 6 H. Strigis in Saxony.

Variolite.—Reniform; incrusting; weak resinous; greasy feel; green. G. = 2-31...2-38; H. = 5. In the closed tube it yields much water, and assumes a rose-red colour. Chem. com. chiefly phosphate of alumina, with water, magnesia, protoxide of iron, and chrome-oxide. Plauen in the Voigtländer.

*32. Wavellite, Lasionite.—AP P + 12 H.

Rhombic; ∞P 126° 25', P∞ 106° 46'; crystals ∞P∞ (P), ∞P (d), P∞ (e) (fig. 109); but generally small, acicular, and in hemispherical radiated fibrous masses. Cleavage, along ∞P and P∞ rather perfect. H. = 3-5...4; G. = 2-3...2-5. Translucent; vitreous. Colourless, but generally yellowish or grayish, sometimes green or blue. In closed tube yields water. B.B. in the fireplaces colours the flame weak bluish-green; on charcoal intumesces, and becomes snow-white. Soluble in acids. Chem. com. 38-0 alumina, 35-3 phosphoric acid, and 26-7 water; but generally traces of fluoric acid (2 per cent.). Beraun in Bohemia, Amberg in Bavaria, Frankenberge in Saxony, Tanne in the Harz, Barnstaple in Devonshire, St Austell in Cornwall, near Clonmel, Cork, and Portrush, Ireland, and in the Shiant Isles in Scotland; also in New Hampshire and Tennessee.

33. Wagnerite.—Mg P + Mg F.

Monoclinohedric; C = 63° 25', ∞P 57° 35', P∞ 71° 53'. Cleavage, prismatic and orthodiagonal imperfect. Fracture conchoidal or splintery. H. = 5...5-5; G. = 3-0...3-1. Translucent or transparent; resinous. Wine-yellow, honey-yellow, and white. B.B. fuses with great difficulty in thin splinters to a dark greenish-gray glass. Chem. com. 43-32 phosphoric acid, 11-35 fluorine, 37-64 magnesia, and 7-69 magnesium; but with 3 to 4-5 iron protoxide, and 1 to 4 lime. Very rare; Werfen in Salzburg.

34. Amblygonite.—(Al P + (Li, Na) P + Al F) + (Li, Na) F.

Rhombic; coarse granular. Cleavage, ∞P 106° 10', tolerably perfect. Fracture uneven and splintery. H. = 6; G. = 3-3...3-1. Translucent; vitreous; pearly on ∞P. Grayish or greenish-white to pale mountain-green. In closed tube yields water, sometimes corroding the glass. B.B. fuses very readily to a transparent glass, opaque when cold. Finely pulverized it is slowly soluble in acids. Chem. com. 47-9 phosphoric acid, 3-5 alumina, 6-9 lithia, 6 soda, and 8-3 fluorine. Penig in Saxony.

Family V.—Leucite.

Tesseral. H. = 5...6; G. = 2-2...2-5. All fusible except leucite, and all soluble and mostly gelatinize in hydrochloric acid. They are mostly silicates of alumina and of alkalies (or lime), often with chlorine, sulphur, or sulphuric acid. Their colours are white, gray, or often blue. They are mostly found imbedded in volcanic rocks.

35. Leucite.—(Al Si + K Si) or 3 Al Si + K Si.

Tesseral; only 202 (fig. 6). The crystals generally single. Cleavage, hexahedral very imperfect. Fracture conchoidal. H. = 5-5...6; G. = 2-4...2-5. Transparent to translucent on the edges; vitreous, inclining to resinous. Colourless, but grayish, yellowish, or reddish-white, or gray; streak white. B.B. infusible; with cobalt solution becomes blue. Soluble in h. acid, without gelatinizing. Chem. com. 55-7 silica, 31-1 alumina, and 21-2 potash. Abundant in the lavas of Vesuvius, the tufts near Rome, and the peperino of Albano; also at the Kaiserstuhl, and near Lake Laach. Readily distinguished from Analcime by its infusibility and by never showing faces of the cube.

36. Porcelain Spar.—3 Al Si + (Ca Na) Si + K Cl.

Rhombic; ∞P 92° nearly. Massive and coarse granular. Fracture uneven. H. = 5-5; G. = 2-67...2-68. Translucent, or only on the edges; vitreous or pearly. Yellowish or bluish-white, or pale gray. B.B. fuses easily with intumescence to a colourless vesicular glass. Soluble under gelatinizing in con. h. acid. Chem. com. 49-55 silica, 27-40 alumina, 15-62 lime, 4-75 soda, 1-39 potassium, and 1-29 chlorine. Obernellen near Passau (Passaute), forming porcelain earth when decomposed.

37. Sodaite.—3 (Al Si + Na Si) + Na Cl.

Tesseral; ∞O (fig. 3); massive and granular. Cleavage, ∞O more or less perfect. Fracture conchoidal or uneven. H. = 5-5; G. = 2-28...2-29. Translucent; vitreous, inclining to resinous. White, gray, green, and rarely blue. B.B. becomes white and fuses easily alone, sometimes intumesces to a clear glass; with difficulty in borax. Gelatinizes with acids. Chem. com. 37-8 silica, 31-3 alumina, 25-3 soda, and 5-6 chlorine. Greenland, Vesuvius, Valle di Noto in Sicily, Lake Laach, Ilmen Hills, Fredrikshavn in Norway, and Litchfield in Maine.

38. Hauyne.—3 (Al Si + Na Si) + 2 Ca S.

Tesseral chiefly ∞O, but more common in grains. Cleavage ∞O more or less perfect. H. = 5...5-5; G. = 2-4...2-5. Semi-transparent or translucent; vitreous or resinous. Azure or sky blue; streak bluish-white. B.B. decrepitates violently, and melts to a bluish-green vesicular glass. Soluble, and gelatinizes in h. acid. Chem. com. 32-5 silica, 27-1 alumina, 16-4 soda, 9-9 lime, and 14-1 sulphuric acid. Vesuvius, Mount Vultur near Melfi, the Campagna of Rome, and Niedermendig near Andernach.

39. Nosean.—3 (Al Si + Na Si) + Na Si.

Tesseral, like Hauyne, but oftener granular. H. = 5-5; G. = 2-25...2-27. Translucent; vitreous to resinous. Ash or yellowish gray, sometimes blue, brown, or black. B.B. becomes paler, and melts to a vesicular glass. Soluble in acids. Chem. com. 36-65 silica, 30-59 alumina, 24-82 soda, **Family VI.—Zeolites.**

Crystallization chiefly rhombic and monoclinohedric; also tetragonal and tesserai. \( H = 3 \ldots 6 \), or mostly scratched by steel; \( G = 2 \ldots 3 \). Mostly hyaline, and white or red, gray or yellow coloured. Cleavage generally distinct. All yield water in closed tube; all fusible B.B.; all soluble in acids, and mostly gelatinize or deposit silica. They are hydrated silicates of alkalies, or alkaline earths, mostly with silicates of aluminas, but rarely contain magnesia. They are generally found in amygdaloidal cavities or fissures of trap or plutonic rocks, apparently as deposits from water percolating through them. Also in veins, but rare.

*43. Analcime.* \[ \text{Al}_2\text{Si}_3 + \text{Na}_2\text{Si}_2 + 2\text{H}, \text{or} \]

Tesseral; crystals 20°, seldom \( \infty O \times 20° \) (fig. 115) in druses; also granular. Cleavage hexahedral, very imperfect; fracture uneven. \( H = 5 \); \( G = 2 \ldots 2 \). Transparent to translucent on the edges; vitreous. White, grayish, greenish, yellowish, or reddish white; also flesh-red, and very rarely leek-green. B.B. melts quietly to a clear glass. Completely soluble and gelatinizes in h. acid. Chem. com. 55-2 silica, 22-9 alumina, 18-9 soda, and 8 water, with occasionally a little potash or lime. Seisser Alp in Tyrol, Dumbarton in Scotland, and in Siebenburg; Cypriote Islands, Sicily; the Vicentine, Norway, Faroe, Iceland, Nova Scotia; also Giant's Causeway; and the Hebrides, Glenfarg, Salisbury Crags, and other parts of Scotland. Sarcosite, Cuboit, and the Cluthalite, from near Dumbarton, are varieties.

*44. Natrolite, Mesotype.* \[ \text{Al}_2\text{Si}_3 + \text{Na}_2\text{Si}_2 + 2\text{H}, \text{or} \]

Rhombic; \( \infty P 91° \), \( \infty P \) polar edges 143° 20', and 142° 40', middle edges 53° 20'; crystals, \( \infty P \), \( P \) (fig. 111), fine prismatic, acicular or fibrous, and radiating. Cleavage, \( \infty P \) perfect. \( H = 5 \ldots 5 \); \( G = 2 \ldots 2 \). Pellucid; vitreous. Colourless or grayish-white, but sometimes bluish or yellow, seldom red or brown. Is not pyroelectric. B.B. becomes obscure and melts quietly to a clear glass. Gelatinizes in h. acid. Chem. com. 48 silica, 26-6 alumina, 16-1 soda, and 9-3 water, with a little lime and iron oxides. Clermont in Auvergne, Alpstein in Hessa, Hohentwiel in Swabia, Norway; in Scotland, as in Mull, Canna, and near Tantallon Castle; and in Ireland, Nova Scotia, and other countries. Bergmannite and Radiolite are varieties. Galactite, \( H = 4 \), with 4 lime and 10-5 water. Glenfarg, Kilpatrick, and Bishopstown, probably distinct.

*45. Scolecite, Needlestone.* \[ \text{Al}_2\text{Si}_3 + \text{Ca}_2\text{Si}_3 + 3\text{H}, \text{or} \]

Monoclinohedric; \( C = 89° 6' \), \( \infty P 91° 35' \), \( P 144° 20' \); crystals, \( \infty P \), \( P \), prismatic or acicular. Twin crystals very common, united by a face of \( \infty P \), and one face with feathery striae (fig. 112); also massive and radiating. Cleavage, \( \infty P \) rather perfect. \( H = 5 \ldots 5 \); \( G = 2 \ldots 2 \). Pellucid; vitreous, fibrous varieties silky. Snow-white, grayish, yellowish, and reddish white. Distinctly pyro-electric. B.B. bends and twists in a vermicular manner, and melts easily to a porous glass. In h. acid dissolves and gelatinizes. Chem. com. 46-6 silica, 25-8 alumina, 14 lime, and 13-6 water. Very fine on Staffa; at Beruford in Iceland; in Faroe, Greenland; and the Vendyiah Mountains in India; also in Tyrol, Ireland, &c.

The following are either varieties of, or closely allied to, Scolecite or Natrolite:

*Melolite,* with 4 to 5 soda; Staffa, Antrim, and Iceland.

*Caporcianite,* reddish-gray, radiating fibrous; Caporciano, Tuscany.

*Lepidinite,* fine scaly, flesh-red. \( G = 1-953 \); \( H = 2 \ldots 5 \). Glenarm, Ireland.

*Poonahlite,* rhombic prisms of 92° 20', otherwise like Scolecite, from Poonah in Hindustan.

*Brevicite,* radiated, massive, white, reddish-gray, or dark-red; Brevig.

*Harringtonite,* compact, earthy, snow-white; Portrush in Ireland.

*Antrimolite,* white, fibrous, and opaque. \( G = 2-096 \); \( H = 3-75 \). Antrim.

*Stellite,* fine rhombic prisms grouped in concentric stars. White, transparent, silky. \( H = 3 \ldots 3 \); \( G = 2-612 \). Kilsyth, Scotland.

*Mesole* or *Farielle,* radiating, fibrous; transparent, pearly; white, yellow, or gray. \( H = 3 \). Chem. com. 41-3 silica, 28-4 alumina, 11-5 lime, 5-7 soda, and 13-2 water. Faroe, Schonen; Storr, Uig, and Portree, in Skye. The last is perhaps a distinct species.

*46. Thomsonite, Comp-tonite.* \[ \text{Al}_2\text{Si}_3 + \text{Ca}_2\text{Si}_3 + 7\text{H}, \text{or} \]

Rhombic; \( \infty P 90° 40' \), usually like fig. 113, terminating in an extremely obtuse dome of 177° 35', like the basis with the plane broken. In druses, fan-shaped or radiated. Cleavage, macrodialonal and brachydialonal equally perfect. \( H = 5 \ldots 5 \); \( G = 2 \ldots 2 \). Translucent, but often obscure; vitreous, sometimes pearly. White. B.B. intumesces, becomes opaque, and fuses with difficulty to a white enamel. Soluble, and gelatinizes in h. acid. Chem. com. 38-2 silica, 31-6 alumina, 17-2 lime, with 1 to 8 soda, and 13 water. Vesuvius, Sicily, Bohemia, Tyrol, Iceland, Faroe, Scotland (Lochwinnoch, Kilpatrick Hills), and Nova Scotia. Chalcedony, a compact variety; Antrim.

47. Stilbite, Desmine. \( \text{Al}^3\text{Si}^3 + \text{Ca}^2\text{Si}^2 + 6\text{H}_2\text{O} \) or \( \text{Al}^3\text{Si}^3 + \text{Ca}^2\text{Si}^2 + 6\text{H}_2\text{O} \).

Rhombic; P polar edges, 119° 16', and 114°; crystals, \( \text{P}^\infty(M) \), \( \text{P}^\infty(T) \), \( \text{P}^\infty(r) \), \( \text{OP}(P) \) (fig. 114), broad pyramidal, very often fascicular or diverging; also radiating or broad columnar, or macle. Cleavage, macrodiagonal very perfect. \( H = 3-5...4 \); \( G = 2-1...2-2 \). Translucent, or only on the edges; vitreous; pearly on \( \text{OP}^\infty \). White, red, gray, yellow, and brown. B.B. intumesces greatly, and melts with difficulty to a white enamel. Decomposed by c.h.acid, leaving slimy silica. Chem. com. 58-2 silica, 16 alumina, 8-8 lime, with 1 to 3 soda or potash, and 17 water. Andreasberg in the Harz, Kongsberg and Arendal, Iceland, Faroe, and the Venayah Mountains in Hindostan; in Scotland, in Skye, Kilpatrick, Kilmacolm, and Arran. Spherostilbite and Hypostilbite are related species. Edelforsite; fibrous or columnar; \( H = 6 \); \( G = 2-6 \); is a stilbite with two atoms less water, or a laumontite mixed with quartz. Edelfors in Sweden.

48. Heulandite. \( \text{Al}^3\text{Si}^3 + \text{Ca}^2\text{Si}^2 + 5\text{H}_2\text{O} \) or \( \text{Al}^3\text{Si}^3 + \text{Ca}^2\text{Si}^2 + 5\text{H}_2\text{O} \).

Monoclinohedric; \( C = 63° 40' \), \( P = 50° 20' \); crystals \( \text{P}^\infty(P) \), \( \text{P}^\infty(O) \), \( \text{P}^\infty(F) \) (fig. 115); mostly tabular, rarely prismatic in druses or radiated lamellar. Cleavage, clinodiagonal very perfect; brittle. \( H = 3-5...4 \); \( G = 2-1...2-2 \). Transparent to translucent on the edges; vitreous or pearly. White, but often flesh or brick-red, and yellowish or hair-brown. B.B. exfoliates, intumesces, and melts to a white enamel. Soluble in h. acid, leaving slimy silica. Chem. com. 59-9 silica, 16-7 alumina, 9 lime, and 14-5 water. Arendal, Kongsberg, Andreasberg, Fassa Valley, Iceland, Faroe, Nova Scotia, New Jersey, and the Venayah Mountains, Hindostan; at Campsie, in Skye, and other parts of Scotland. Beaumontite is the same; Baltimore.

49. Brewsterite. \( \text{Al}^3\text{Si}^3 + (\frac{3}{2}\text{Sr} + \frac{1}{2}\text{Ba})\text{Si}^2 + 5\text{H}_2\text{O} \).

Monoclinohedric; \( C = 86° 20' \); crystals short prismatic, of several vertical prisms, bounded by an extremely obtuse clinodome (172°) (fig. 116), are mostly small. Cleavage, clinodiagonal very perfect. \( H = 5...5-5 \); \( G = 2-12...2-2 \). Pellucid; vitreous or pearly. White, gray, yellow, brown, or green. B.B. froths, intumesces, and fuses to a porous glass. Soluble in h. acid, and gelatinizes. Chem. com. 54-3 silica, 15-0 alumina, 10-1 strontia, 7-4 baryta with 1-3 lime, and 13-1 water; and thus with all the three alkaline earths. Strontian in Scotland, Giants' Causeway, Freiburg in the Breisgau, and the Pyrenees.

50. Epistilbite. \( \text{Al}^3\text{Si}^3 + \text{Ca}^2\text{Si}^2 + 5\text{H}_2\text{O} \).

Rhombic; \( \text{P}^\infty(135°10') \), \( \text{P}^\infty(109°46') \), \( \text{P}^\infty(147°40') \); in long prismatic crystals (fig. 117). Macles united by a lace of \( \text{P}^\infty \) are more common; also massive and granular. Cleavage, brachydiagonal very perfect. \( H = 3-5...4 \); \( G = 2-3...2-4 \). Pellucid; vitreous or pearly. Colourless or white. B.B. melts with intumescence to a porous enamel. Soluble without gelatinizing, but after ignition is insoluble. Chem. com. 59 silica, 17-5 alumina, 9 lime, with 1-5 soda, and 14-5 water, or like Heulandite. Iceland and Faroe; also, it is said, in Skye, and at Portrush in Ireland.

51. Aporophyllite. \( 4\text{Ca}^2\text{Si}^2 + \text{K}^2\text{Si}^2 + 16\text{H}_2\text{O} \).

Tetragonal; \( P = 121° 4' \); crystals, \( \text{P}^\infty(P) \) (fig. 118) and \( \text{OP}^\infty \) are pyramidal, or short prismatic, or tabular; usually in druses or lamellar. Cleavage, basal perfect; \( \text{P}^\infty \) imperfect; brittle. \( H = 4-5...5 \); \( G = 2-3...2-4 \). Pellucid; vitreous; on \( \text{OP}^\infty \) pearly (ichthyophthalm). Colourless, but yellowish, grayish, or reddish white, to rose or flesh red. B.B. exfoliates, intumesces, and melts easily to a white enamel. Powder readily soluble in h. acid, leaving slimy silica. Chem. com. 52-8 silica, 25-4 lime, 5-3 potash, and 16-3 water; in some with 0-24 to 1-54 fluorine. Occurs at Utoe in Sweden, Aussig in Bohemia, the Seisser Alp in Tyrol, St Andreasberg in the Harz, Nertschinsk in Siberia, in Greenland, Iceland, Faroe, and Raith in Fife.

Gyrolite, spherical radiated concretions, with 50-7 silica, 14-8 alumina, 33-24 lime, 0-18 magnesia, and 14-18 water, seems a variety; Storr in Skye. Also Xylochor, from Iceland.

52. Okenite, Dyclasite. \( \text{Ca}^2\text{Si}^2 + 2\text{H}_2\text{O} \).

Rhombic; \( \text{P}^\infty(122°19') \); usually fine columnar or fibrous. \( H = 5 \); \( G = 2-28...2-36 \). Pellucid; slightly pearly. Yellowish to bluish-white. B.B. froths up and melts to an enamel. In powder easily soluble in h. acid, leaving gelatinous flakes; after ignition insoluble. Chem. com. 57 silica, 26 lime, and 17 water. On Disco Island, Greenland, Faroe, and Iceland.

53. Pectolite. \( 8\text{Ca}^2\text{Si}^2 + \text{Na}^2\text{Si}^2 + 3\text{H}_2\text{O} \), or \( 6\text{R}^2\text{Si}^2 + \text{H}_2\text{O} \).

Monoclinohedral (5), but only spheroidal, radiating, and columnar. \( H = 5 \); \( G = 2-69...2-74 \). Translucent on the edges; slightly pearly. Grayish-white or yellowish. B.B. melts easily to a white enamel-like glass. Soluble in h. acid, leaving flaky silica; after ignition gelatinizes perfectly. Chem. com. 52-1 silica, 34-2 lime, 9-5 soda, with 0-6 to 1-6 potash and 4-2 water. Monte Baldo, Monte Monzon in Tyrol, Kilsyth (Wollastonite), Ratho, Corstorphine near Edinburgh, and Storr in Skye.

54. Levynite. \( \text{Al}^3\text{Si}^3 + \text{Ca}(\text{K}, \text{Na})\text{Si}^2 + 4\text{H}_2\text{O} \).

Rhombohedric; \( R = 75° 29' \); crystals, \( \text{OR}, \text{R} = \frac{1}{2}\text{R} \), thick tabular, in perfect intersecting macles (fig. 119). \( H = 4 \); \( G = 2-1...2-2 \). Chem. com. 44-5 silica, 23-8 alumina, 10-7 lime, 1-6 potash, 1-4 soda, and 17-4 water. Otherwise like chabasite. Faroe, Glenarm, Skye, and Hartfield Moss in Renfrewshire.

55. Charasite, Lime-Ch. \( \text{Al}^3\text{Si}^3 + \text{Ca}(\text{Na}, \text{K})\text{Si}^2 + 6\text{H}_2\text{O} \).

Rhombohedric; \( R = 94° 46' \); \( R \) mostly alone, but also with \( -\frac{1}{2}R \) and \( -2R \). Intersecting macles very common; crystals in druses and striated. Cleavage, \( R \) rather perfect. \( H = 4...4-5 \); \( G = 2-2...2-2 \). Transparent to translucent; vitreous. Colourless, grayish, yellowish, reddish to flesh-red. B.B. fuses to a finely porous enamel. Soluble in h. acid, leaving slimy silica. Chem. com. 48-2 silica, 20 alumina, 10-8 lime, with 0 to 2-5 soda, and 0-2 to 3 potash, and 21 water. Faroe, Iceland, Greenland, Aussig in Bohemia, Giants' Causeway, Kilmacolm in Renfrewshire, in Skye, and other places in Scotland. Phacolite, with rather less silica and more alumina, is a variety; Leipa in Bohemia.

56. Gmelinite, Soda-Chabasite. \( \text{Al}^3\text{Si}^3 + \text{Na}(\text{Ca}, \text{K})\text{Si}^2 + 6\text{H}_2\text{O} \).

Hexagonal; \( P = 80° 8' \); crystals \( \text{P}^\infty \), \( \text{OP}^\infty \) (fig. 120). The faces of \( \text{P}^\infty \) striated parallel to their polar edge; those of the prism horizontally. Cleavage, $\alpha P$ distinct.

Gelatinizes with h. acid; otherwise like chabasite. Chem. com. 47-6 silica, 19-7 alumina, 12 soda, with 3 to 5 lime, and 0-4 to 2 potash, and 20-7 water. Glenarm in Antrim, Vicenza (Sarcolite). Lederite, with only 9 per cent. water, seems a variety; Cape Blomidon, Nova Scotia.

57. Faujasite.—$2 \text{Al}^3\text{Si}^3 + (\text{Ca}, \text{Na})^2 \text{Si}^3 + 18 \text{H}_2$. Tetragonal; $P = 105^\circ 30'$. Fracture uneven; brittle. Scratches glass. $G = 1-923$. Transparent; vitreous or adamantine. White or brown. B.B. intumesces and fuses to a white enamel. Soluble in h. acid. Chem. com. 46 silica, 17 alumina, 5 lime, 5 soda, and 27 water. Kaiserstuhl.

58. Edingtonite.—$4 \text{Al}^3\text{Si}^3 + 3 \text{Ba} \text{Si}^3 + 12 \text{H}_2$. Tetragonal, hemihedral; $P = 87^\circ 9'$; formed as a sphenoid ($P$), with polar edges $92^\circ 5'$, and $\alpha P (n)$, polar edges $129^\circ 5'$, and $\alpha P (m)$ (fig. 121). Cleavage, $\alpha P$, perfect. $H = 4...4\frac{1}{2}$; $G = 2-7...2-75$. Translucent; vitreous. Grayish-white. B.B. fuses difficultly to a colourless glass. Chem. com. 37-3 silica, 23-7 alumina, 26-5 barya, and 12-5 water (analysis). Kilpatrick Hills, Dumbartonshire.

59. Harmotome, Cross-stone.—$3 \text{Al}^3\text{Si}^3 + \text{Ba} \text{Si}^3 + 5 \text{H}_2$. Rhombic; $P$ polar edges $119^\circ 4'$, and $121^\circ 6'$, and $\alpha P = 88^\circ 14'$; crystals, $\alpha P = q$, $\alpha P = o$, $P$, $P \alpha$, short prismatic. Generally in perfectly intersecting macles (fig. 122). Cleavage, brachydioanal imperfect, macrodional less distinct; brittle; fracture uneven. $H = 4-5$; $G = 2-3...2-5$. Translucent; vitreous. Colourless, but white, gray, yellow, brown, or red. B.B. fuses rather difficulty but quietly to a clear glass. Soluble, but not readily, in h. acid, with deposition of silica. Chem. com. 47-25 silica, 15-67 alumina, 23-39 barya (with 1 to 3 lime and 1 to 2-5 potash), and 18-76 water. Andreasberg, Kongsberg, Oberstein; Dumbartonshire and Strontian (Morenite), Scotland.

60. Phillipsite.—$3 \text{Al}^3\text{Si}^3 + (\text{Ca}, \text{K}) \text{Si}^3 + 5 \text{H}_2$. Rhombic; $P$ polar edges $119^\circ 18'$ and $120^\circ 42'$. Forms, macles, and other characters like harmotome. $G = 2-15...2-20$. B.B. fuses easily with slight intumescence; gelatinizes in h. acid. Chem. com. 48-6 silica, 20-2 alumina, 7-3 lime, 6-2 potash, and 17-7 water. Giessen, Marburg, Cassel, Iceland, and the Giants' Causeway.

61. Herschelite.—$3 \text{Al}^3\text{Si}^3 + (\text{Na}, \text{K}, \text{Ca}) \text{Si}^3 + 3 \text{H}_2$. Hexagonal; $P$ polar edges, $124^\circ 40'$; crystals $\alpha P$, $P$, $P \alpha$. $H = 4-5$; $G = 2-06$. Translucent; pearly; white. B.B. fuses readily to a white enamel. Chem. com. 48-5 silica, 20-1 alumina, 9-2 soda, 4-6 potash (with 0-2 to 5 lime), and 17-6 water. Aci Reale and Palagonia in Sicily.

62. Zragonite.—$2 \text{Al}^3\text{Si}^3 + 2 (\text{Ca}, \text{K}) \text{Si}^3 + 7 \text{H}_2$. Rhombic; $P$ polar edges $120^\circ 37'$ and $121^\circ 44'$; crystals single or in groups. $H = 5$, on angles and edges = 7 or more; $G = 2-213$. Transparent; vitreous. Colourless, white, or bluish. B.B. becomes white, falls down, shines, and melts to a clear glass. Capo di Bove. Variety of Phillipsite (?).

63. Gismondine, Abrazite.—$3 \text{Al}^3\text{Si}^3 + \text{Ca} (\text{K}) \text{Si}^3 + 4 \text{H}_2$. Tetragonal (or rhomboic ?); $P = 92^\circ 30'$; crystals, $P$ or with $\alpha P \alpha$, in groups. Cleavage, $P$ imperfect. $H = 5$, on edges and angles = 6; $G = 2-265$. Semitransparent to translucent; vitreous. Grayish-white to pale-red. B.B. intumesces, shines, and melts to a white enamel. Chem. com. 35 silica, 29 alumina, 15-7 lime (with 2-8 potash), and 20-3 water. Vesuvius, Aci Castello, and Capo di Bove.

64. Laumontite.—$3 \text{Al}^3\text{Si}^3 + \text{Ca} \text{Si}^3 + 4 \text{H}_2$. Monoclinohedric; $C = 68^\circ 40'$, $\alpha P = 86^\circ 15'$, $\alpha P = 2 P = 113^\circ 30'$; crystals prismatic, also columnar. Cleavage, prismatic perfect; clinodiamondal in traces; rather brittle. $H = 3...3\frac{1}{2}$ (when fresh = 5...6?); $G = 2-2...2-3$. Pellucid; vitreous; on cleavage pearly. White, grayish, yellowish, and reddish. In the air soon decomposed, B.B. intumesces and melts easily to a white enamel, which becomes clear in a stronger heat. Soluble and gelatinizes in h. acid. Chem. com. 51-8 silica, 21-5 alumina, 11-3 lime, and 15-4 water. Huelgoet in Brittany, Eule near Prague, Fahlun, Iceland, Faroe, Snizort and Storr in Skye, Dumbarton, and other parts of Scotland, and in North America.

65. Leonardite.—$4 \text{Al}^3\text{Si}^3 + 3 \text{Ca} \text{Si}^3 + 12 \text{H}_2$. Monoclinohedric; $\alpha P = 83^\circ 30'$, $\alpha P = OP = 114^\circ$; crystals, $\alpha P$, $P$, prismatic, and grouped in bundles; also granular or columnar. Cleavage, $\alpha P$ very perfect, basal imperfect. Very friable. $H = 3...3\frac{1}{2}$; $G = 2-25$. Translucent on the edges; pearly; yellowish-white. B.B. exfoliates, froths, and melts easily to a white enamel. Becomes opaque, and decomposes quickly in the air. Chem. com. 53-9 silica, 23-8 alumina, 9-8 lime, and 12-5 water. Schemitz.

66. Glottalite.—$3 \text{Al}^3\text{Si}^3 + 3 \text{Ca} \text{Si}^3 + 8 \text{H}_2$. Tesselar; $O$ and $\alpha O$; in druses. $H = 3...4$; $G = 2-18$. Highly translucent; vitreous. Colourless or white. B.B. melts with intumescence to a white enamel. Chem. com. 37-4 silica, 15-6 alumina, 25-3 lime, and 21-7 water. Near Port-Glasgow. Probably chabasite.

**FAMILY VII.—Mica.**

Crystallization monoclinohedric or rhombic, and hexagonal or rhombohedric. Cleavage mostly very perfect in one direction (basal), and thin laminae flexible. Pellucid, with a strong, often semimetallic lustre. $H = 2...3$, rarely 1...6; $G = 2-5...3$. B.B. mostly fusible. Are silicates of alumina, with silicates of potash, magnesia, lithia, and protoxides of iron and manganese, with or without water. They are mostly constituents of the plutonic or volcanic rocks.¹

**67. Potash-mica, Muscovite.**

Monoclinohedric, or probably rhombic. Crystals chiefly rhombic or six-sided tables, with $\alpha P = 120^\circ$ and $60^\circ$ nearly. Imbedded, or in druses; also scaly, foliated, or lamellar. Macles rather rare. Cleavage, basal highly perfect; sectile, and in thin laminae elastic. $H = 2...3$; $G = 2-5...3-1$. Pellucid in various degrees; optically biaxial; metallic-pearly, on some faces vitreous. Colourless, but white, gray, green, red, brown, black, and rarely yellow. In closed tube usually yields water, with traces of fluorine. B.B. loses its transparency, and fuses to an obscure glass or white enamel. Not affected by h. or s. acids. Chem. com. very variable, but nearly 48 silica, 39-8 alumina, and 12-2 potash; but analyses give 40 to 48 silica, 32 to 37 (rarely 9 to 10) alumina, 3 to 9 (or 36) peroxide of iron, 1 to 2 peroxide of manganese, 5 to 10 potash, 1 to 3 protoxide of iron (with traces of lime, magnesia, and soda), and most 1 to 4 water and 1 to 3 fluorine. The green micas (Fuchsite) also 4 to 6 chrome oxide. Abundant as a constituent of granite, gneiss, mica-slate, and other rocks. Large plates in Norway, Sweden, and especially in

¹ Neither the optical nor crystallographical characters of the micas, Nos. 67 to 71, are well determined. The magnesia micas were formerly regarded as monaxial and hexagonal, but now appear to be biaxial, with the angle between the axes small, in blotto under 5°, often 0° to 1° or 2°; in phlogopite, 5° to 20°. The crystallization of the potash micas and lepidolite is more probably rhomboic. The chem. com. also cannot be represented by any general formula. Mineralogy.

Siberia, often a yard in diameter, and used for windows, but become white on exposure. Fine crystals, Vesuvius, St Gotthardt, Pargas, Arendal, Utoe, Fahlun, Kimito, Cornwall, and Aberdeenshire.

68. DAMOURITE.—$3 \text{Al}^3\text{Si} + \text{K}^+ \text{Si}^2 + 2 \text{H}$.

Fine foliated. $H = 1-5; G = 2-7...2-8$. Translucent on the edges; pearly; yellowish-white. B.B. yields water, intumesces, becomes milk-white, and melts with difficulty to a white enamel. Soluble in sulphuric (not in h.) acid, leaving silica. Chem. com. 45-7 silica, 38-1 alumina, 11-7 potash, and 4-5 water. Pontivy in Brittany. The mica slate of St Gotthardt (Paragonite) is similar externally, but contains 50-20 silica, 35-90 alumina, 2-36 iron peroxide, 8-45 soda, and 2-45 water; and is fusible B.B. Didomite from Zillerthal, and Margarodite from Connecticut, are similar hydrous micas.

69. LITHIA-MICA, Lepidolite. $\{3 \text{Al}^3\text{Si}^2 + 2 \text{Li}^+ \text{Si} + (\text{KF}, \text{Si}^2)$.

Crystallization and physical characters like potash-mica, but colour often rose or peach-blossom red. In the closed tube shows evident fluorine reaction. B.B. melts very easily with effervescence to a colourless, brown, or rarely black magnetic glass, colouring the flame red. Imperfectly soluble in acids, wholly so after fusion. Chem. com. 51-6 silica, 28-5 alumina, 8-7 potash, 5-3 lithia, and 5-9 fluoric acid; analyses give 46 to 52 silica, 20 to 29 alumina, 0 to 18 iron peroxide, 0 to 5 manganese peroxide, 5 to 10 potash, 2 to 6 lithia, 4 to 6 fluorine, and 0 to 15 soda. Cornwall, Bohemia, Saxony; and also at Portsoy (serpentine), Loch Fine, and Balnahulish (limestone), in Scotland. It is sometimes used as an ornamental stone.

70. BIOTITE, Magnesia-Mica. $\{\text{Al}^3\text{Si}^2 + (\text{Mg}, \text{K}, \text{Fe})^3\text{Si}, \text{or Al}^3\text{Si} + \text{R}^3\text{Si}\}$.

Rhombohedral; $R 71° 4'$ to about 73° (but perhaps rhombic); crystals mostly tabular, rarely short prisms. Cleavage, basal very perfect; sectile; in thin plates elastic. $H = 2-5...3; G = 2-85...2-9$. Transparent, but often only in very thin plates (and generally monoaxial?); metallic pearly. Usually dark-green, brown, or black; streak greenish-gray or white. B.B. difficultly fusible to a gray or black glass. Completely soluble in con. s. acid, leaving white pearly plates of silica. Chem. com. very variable, but analyses give 40 to 42 silica, 13 to 16 alumina, 0 to 20 iron peroxide, 0 to 20 iron protoxide, 10 to 25 magnesia, 4 to 10 potash, 0 to 2 fluorine, and 1 to 3 water. Pargas, Bodenmais, Monroe in New York, Greenland, near Aberdeen, and in other parts of Scotland. Rubellan, brownish-red, Bohemia and Saxony, seems a variety.

71. PHLOGOPITE.—$\text{Al}^3\text{Si} + (\text{Mg}, \text{K}, \text{Na})^3\text{Si}$.

Rhombic (or rhombohedral?), in rhombic or hexagonal prisms. Cleavage, basal. Yellow or copper-red; also colourless, white, and brown. B.B. fuses to a white enamel. Chem.com.38 to 42 silica, 13 to 20 alumina, 2 to 7 iron oxides, 25 to 30 magnesia, 6 to 10 potash, 1 to 5 soda, and 0-2 to 4 fluorine. In limestones, New York, Vosges Mountains, Sala.

72. LEPIDOMELANE.—$(\text{Al}, \text{Fe})^3\text{Si} + (\text{Fe}, \text{K})^3\text{Si}$.

Hexagonal, small six-sided tables. Cleavage, basal perfect; rather brittle. $H = 3; G = 3-0$. Highly vitreous; opaque and raven-black; or translucent and leek-green; streak mountain-green. B.B. becomes brown, and fuses to a black magnetic bead. Soluble in h. acid, leaving pearly scales of silica. Chem. com. 37-4 silica, 11-6 alumina, 27-7 iron peroxide, 12-4 iron protoxide, 9-2 potash, with 0-6 magnesia and lime. Persberg, Sweden.

73. CHLORITOID.—$3 \text{Fe}^3\text{Si} + (\text{Fe}, \text{Mg})^3\text{Si}$.

Granular, foliated. Cleavage, in one direction perfect; brittle. $H = 5-5...6; G = 3-55$. Opaque; weak pearly. Blackish-green; streak greenish-white. B.B. infusible, but becomes darker and magnetic. Not affected by acids.

Chem. com. 26-2 silica, 43-4 alumina, and 30-4 iron protoxide, with 0 to 4 magnesia, and mostly 6 to 7 water. Kosolbrod in the Ural, Tyrol. Sissmundite, St Marcel in Piedmont, is similar; and Masonite, from Rhode Island.

74. OTTRELITE.—$3 \text{Fe}^3\text{Si} + 3 (\text{Fe}, \text{Mn})^3\text{Si} + 3 \text{H}$.

Thin hexagonal tables. Cleavage, parallel to the lateral faces, rather perfect. Scratches glass. $G = 4-4$. Translucent; vitreous. Greenish or blackish-gray. B.B. melts difficulty on the edges to a black magnetic globule. Powder soluble in warm s. acid. Chem. com. 43-9 silica, 24-3 alumina, 17-0 iron protoxide, 8-5 manganese protoxide, and 6-3 water. In gray clay-slate at Ottrelz in Belgium.

75. CHLORITE (Rip). $\{2 \text{R}^3\text{Si} + \text{R}^3\text{Si} + 3 \text{H}$, or dolite, G. Rose). $\{3 \text{R}^3\text{Si} + \text{R}^3\text{Si} + 9 \text{H}$ (Rams).

Hexagonal; $P 106° 50'$; crystals tabular of OP. $\infty P$, or OP. $P_1$ (fig. 123), often in comb-like or other groups; generally foliated and scaly. Cleavage, basal perfect; lamina flexible, but not elastic. $H = 1...1-5; G = 2-78...2-96$. Thin plates transparent or translucent; pearly. Leek to blackish green, often red transverse to the chief axis; streak greenish-gray. In the closed tube yields water. B.B. difficultly fusible on thin edges; soluble in con. sul. acid. Chem. com. when 4 R $= 3 \text{Mg}^3\text{Fe}_2 = 26-3 \text{sil}, 21-8 \text{al}, 25-5 \text{mag}, 15-0 \text{Fe}, \text{and} 11-5 \text{water}$, $= 2 \text{Mg}^3\text{Fe}_2 = 24-6 ... 20-1 ... 16-9 ... 28-5 ... 10-9 ...$

but the analyses variable. Common in the Alps, Scandinavia, the Ural, the Harz, Cornwall, and many parts of Scotland.

76. RIPIDOLITE, Penninite $\{3 \text{Mg}^3\text{Si} + \text{Mg}^3\text{Al} + 4 \text{H}$, or Chlorite, G. Rose). $\{3 \text{R}^3\text{Si} + \text{R}^3\text{Si} + 9 \text{H}$ (Rams).

Rhombohedral ($?) ; $R 68° 15'$; crystals chiefly tabular, in comb-like or fan-shaped groups. Cleavage, basal very perfect; sectile and flexible, but not elastic. $H = 2...3; G = 2-6...2-77$. Translucent, in thin leaves transparent; pearly. Green, but red by light transmitted transverse to the axis; streak greenish-white. B.B. exfoliates, becomes white, and fuses on the edges to a white enamel. Completely soluble in warm s. acid. Chem. com. 33-2 silica, 18-8 alumina, 35-7 magnesia, and 13-8 water, but with 1 to 7 peroxide, and 1 to 6 protoxide of iron. Zermatt in Valais, Schwarzenstein in Tyrol, and Maulenon in the Pyrenees. Leuchtenbergite, yellowish-white, from Slatoust, is the same.

N.B.—Chlorite and Ripidolite may be regarded as one species, with the formula $3 \text{R}^3\text{Si} + \text{Al}^3\text{Si} + 3 \text{H}$ (Rams.)

77. CLINOCHLORIDE.

Monoclinohedral; $C = 76° 4'; OP = 113° 59', OP' = \infty P 102° 8'$. Marles common; also in groups and druses. Other characters and chem. com. like ripidolite, and the two probably identical. West Chester in Pennsylvania, Achmatowsk in Ural, and Leugast in Bavaria (massive).

Epichlorite, Metachlorite, Helmuth, Delesse, and Grengeite are other chlorite-like minerals.

78. TALC.—$\text{Mg}^3\text{Si} + \text{H}$, or $\text{Mg}^3\text{Si} + 2 \text{H}$.

Monoclinohedral; $\infty P_2 = 105° 50'$. Rarely found in six-sided or rhombic tables. Generally massive, granular, or scaly. Cleavage, basal very perfect. Soft, sectile, and flexible, in thin plates. $H = 1; G = 2-68...2-80$. Transparent in thin plates, and optically biaxial; pearly or resinous. Colourless, but generally greenish or yellowish-white, to apple, leek, or olive green. Feels very greasy. B.B. emits a bright light, exfoliates, and hardens ($H = 6$), but is infusible. Not soluble in h. or s. acid before or after ignition. Chem. com. 62-5 silica, 33-9 magnesia, and 3-6 water; but analyses give 57 to 63 silica, 0 to 4-7 alumina, 30 to 35 magnesia, 0 to 2-3 iron protoxide, with traces of lime and nickel oxide, and 2 to 6 water. Greiner in Tyrol, Sala, Fahlun, the Pyrenees, Unst in Zetland, and many parts of the Scottish Highlands (talc-slate). Used as crayons; also for forming crucibles and porcelain.

**Steatite.** Massive. Gray, red, yellow, or green. B.B. melts in fine splinters to a white enamel; but in other respects acts like talc, of which it seems only a compact variety. Briancon, Wunsiedel, the Lizard Point, Cornwall, and near Kirkcaldy, Scotland. Savage nations cut the steatite into culinary utensils. **Potstone** is a mixture of talc, chlorite, and other minerals. Steatite and talc are apparently altered forms of other minerals, chiefly augite and hornblende.

79. **Schillerspar.** \( \text{Mg} (\text{Fe}, \text{Ca})_2 \text{Si}_3(\text{Al}, \text{Fe})_4 + \text{H} \).

Monoclinohedric; only granular and foliated. Cleavage very perfect in one direction, less so in another, meeting at 87°; fracture uneven, splintery. \( H = 3\ldots4; G = 2\ldots2.8 \). Translucent on thin edges; metallic pearly. Olive or pistacio green, yellow, brown, or black; streak greenish white. Imperfectly soluble in h., wholly in s. acid. B.B. becomes magnetic, and fuses in thin splinters on the edges. With borax traces of iron when hot, of chrome when cold. Chem. com. 43 silica, 26 magnesia, 2.7 lime, 7.4 iron protoxide, 3.3 iron peroxide, 2.4 chrome-oxide, 1.7 alumina, and 12.4 water. Baste in the Harz; other localities uncertain. Probably an altered augite.

**Metamict**, massive, asbestosform, weak pearly, and greenish-white; \( H = 2\ldots2.5 \) nearly; \( G = 2.52 \); Schwarzenberg; is closely related.

80. **Pyrosmalite.**

\[ \begin{align*} & \text{Hexagonal;} P_{101}^{\circ} 34^\circ; \text{crystals } \propto P, OP, \text{tabular;} \\ & \text{also granular. Cleavage, basal perfect, } \propto P \text{ imperfect; brittle.} \\ & H = 4\ldots4.5; G = 3\ldots3.2. \text{ Translucent to opaque; resinous, or metallic pearly. Liver-brown to olive-green. B.B.} \\ & \text{fuses to a black magnetic globule. Wholly soluble in c. n. acid. Chem. com. 38.5 silica, 22 iron protoxide, 22 manganese protoxide, 13 iron peroxide, 3.4 hydrochloric acid, and 1.1 water. Nordmark in Sweden.} \end{align*} \]

81. **Cronstedtite.**

\[ \begin{align*} & \text{Chloromelan;} \text{Rhombohedric, chiefly radiated, columnar. Cleavage,} \\ & \text{basal perfect; thin lamina elastic. } H = 2\ldots3; G = 3\ldots3.5. \text{ Opaque or translucent; highly vitreous. Raven-black; streak dark-green. B.B. intumesces, and melts on the edges slowly to a steel-gray globule. Gelatinizes with h. or s. acid. Chem. com. 21.8 silica, 37.6 iron protoxide (with 2.9 manganese protoxide), 25.4 iron protoxide, 4.7 magnesia, and 10.5 water. Przibram in Bohemia; Huel Maulin, Cornwall; and Congonhas do Campo in Brazil (Sideroscholite). \end{align*} \]

82. **Stilpnomelane.** \( (\text{Fe}, \text{Mg})_2(\text{Si}, \text{Al})_3 + 2 \text{H} \).

Massive or radiating-foliated. Cleavage in one direction very perfect; rather brittle. \( H = 3\ldots4; G = 3\ldots3.4 \). Opaque; vitreous, inclining to pearly. Greenish-black; streak greenish. B.B. fuses with difficulty to a black shining globule. Imperfectly decomposed by acids. Chem. com. 45.3 silica, 6.9 alumina, 38.3 iron protoxide (with 2 to 3 magnesia), and 9.5 water. Zuckmantel in Silesia, and Wielburg in Nassau.

83. **Clintonite, Seybertite, Holm-site, Xanthophyllite, Chrysophane.** \( (\text{Fe}, \text{Na}, \text{H}) \).

Hexagonal tables, or massive and foliated. Cleavage very perfect in one direction, traces in another. \( H = 4\ldots6; G = 3\ldots3.16 \). Translucent; pearly on the cleavage planes. Wax-yellow, yellowish, or reddish-brown. Soluble in concentrated acids. B.B. infusible alone, but some become white and colour the flame yellow. Chem. com. uncertain. Amity, New York; Stalstout in the Ural.

**Disterrite, Brandisite,** from Monzoni, in Tyrol; \( H = 5 \) on basis, 6.65 on the prism; when fresh blackish-green, but reddish-brown after exposure; is closely allied.

**Groppite.** Coarse foliated. \( H = 2\ldots5; G = 2\ldots7.3 \). Rose or brown-red. Groppertorp in Sweden.

84. **Margarite, Pearl.**

\[ \begin{align*} & \text{Mica, Emerylite;} \text{Rhombic; rarely in six-sided tables; generally granular foliated. Cleavage, basal very perfect. Thin plates slightly elastic. } H = 3\ldots4\ldots5; G = 3\ldots0.32. \text{ Translucent; vitreous,} \\ & \text{or pearly. Snow-white, reddish-white, or pearl-gray. B.B.} \\ & \text{intumesces and difficultly fusible. Soluble in acids. Chem.} \\ & \text{com. 30.1 silica, 51.2 alumina, 11.6 lime, 2.6 soda, 0.5 to 3} \\ & \text{magnesia, and 4.5 water. Sterzing in Tyrol; Asia Minor and} \\ & \text{Greece, with emery; and in Pennsylvania. Diphanite, in} \\ & \text{hexagonal prisms, bluish-white; B.B. fuses to an enamel;} \\ & \text{from the Ural; is nearly allied.} \end{align*} \]

**Euphylite.** Like mica, but less readily cleavable. \( H = 4; G = 3 \). Pellucid; bright pearly; colourless. B.B. exfoliates with a bright light, and fuses on the edges. Contains 40 silica, 42 alumina, 14 iron peroxide, 14 lime, 33 potash, 5 soda, and 55 water. Unionville, Pennsylvania.

85. **Pyrophyllite.**

\[ \begin{align*} & \text{Rhombic(?), but radiated, columnar, or foliated. Cleavage} \\ & \text{very perfect; flexible; sectile. } H = 1; G = 2\ldots2.8. \text{ Translucent;} \\ & \text{pearly. Light verdigris-green to yellowish-white. B.B.} \\ & \text{swells up with many twistings to a white invisible mass.} \\ & \text{Partially soluble in sulphuric acid. Chem. com. 67 silica,} \\ & \text{28.1 alumina, and 4.9 water, with 0.1 to 4 magnesia and 2.8} \\ & \text{lime. Ural, Spa, Morbihan, and Westana in Sweden.} \end{align*} \]

86. **Anauxite.**

Granular, with a very perfect cleavage in one direction. \( H = 2\ldots3; G = 2\ldots2.6 \). Translucent on the edges; pearly. Greenish-white. B.B. becomes white and fuses on thin edges. Chem. com. 55.7 silica, much alumina, a little magnesia, iron protoxide, and 11.5 water. Bilin in Bohemia.

87. **Pholerite, Nacrite.**

\[ \begin{align*} & \text{Fine scaly. } H = 0\ldots5\ldots1; G = 2\ldots3.5\ldots2.57. \text{ Glimmering} \\ & \text{or pearly. Snow or yellowish white. B.B. infusible.} \\ & \text{Chem. com. 40 silica, 44.4 alumina, and 15.6 water. Fins} \\ & \text{in the Allier dept., Mons, Freiberg, and Naxos.} \end{align*} \]

88. **Rosellan, Polycarite, Rosite.**

\[ \begin{align*} & \text{Small grains, with perfect cleavage. } H = 2\ldots3; G = 2\ldots7.2. \text{ Translucent;} \\ & \text{splendid; fine rose-red. B.B. fuses with difficulty to a white slag.} \\ & \text{Chem. com. 45 silica, 35 alumina, 6.6 potash, 3.6 lime, 2.45} \\ & \text{magnesia, and 6.5 water. Aker and Tunaberg in Sweden.} \end{align*} \]

**Family VIII.—Serpentine.**

Massive or rhombic. \( H = 1\ldots4 \), rarely more; \( G = 2\ldots3\ldots3 \). Often compact or fibrous. B.B. infusible or difficulty. Mostly soluble in acids. Colour often green. Chem. com. generally hydrated silicates of magnesia, partly replaced by protoxide of iron or lime, occasionally also with silicate of alumina or iron peroxide. Occur in plutonic or altered rocks; the serpentine often in large masses or beds.

**89. Serpentine.** \( \text{Mg}_2\text{Si}_2 + 2 \text{H}, \text{or Mg}_2\text{Si}_2 + 6 \text{H} \).

Crystallization uncertain; generally massive, and granular or fibrous. Fracture flat-conchoidal, uneven, or splintery. Sectile and slightly brittle. \( H = 3\ldots3.5; G = 2\ldots2.6 \). Translucent to opaque; dull resinous. Green, gray, yellow, red, or brown, often in spots, stripes, or veins; streak white, shining. Feels greasy. In the closed tube yields water and becomes black. B.B. becomes white, and fuses with much difficulty on thin edges. Soluble in h. or easier in s. acid. Chem. com. 48.35 silica, 42.78 magnesia, and 12.87 water, but with 1 to 8 iron protoxide, and also carbonic acid, bitumen, and chrome oxide. Varieties are—1st, Noble Serpentine; 2nd, Marmolite or foliated; 3rd, Picrolite or fibrous (H = 3½–4½); 4th, Common or compact Serpentine; 5th, Chrysotile (Baltimorite, Metaxite), in fine asbestos-like fibres, easily separated, with a metallic or silky lustre. G = 2.219. Common in Norway, Sweden, North America, the Lizard Point in Cornwall, in Shetland, Portsoy, and many parts of Scotland. The chrysotile, at Reichenstein in Silesia, the Vosges Mountains, and North America.

90. Antigorite.—(Mg, Fe)₃Si⁺ + H (?).

Very thin, straight, slaty laminae. H = 2½; G = 2.62. Transparent or translucent. Dull or blackish lead-green, in some parts with brown spots; streak white. B.B. very thin edges fuse to a yellowish-brown enamel. Chem. com. 46 silica, 2 alumina, 13 iron protoxide, 35 magnesia, and 37 water (but others 13 water). Antigorite in Piedmont.

91. Hydrophrite.—(Mg, Fe)₃Si⁺ + 4 H.

Massive or fibrous. Fracture uneven. H = 3…4; G = 2.65. Mountain-green; streak lighter. B.B. infusible. Chem. com. 36-19 silica, 22-73 iron protoxide, 1-66 manganese protoxide, 21-08 magnesia, 0-89 alumina, 0-12 vanadic acid, 16-09 water. Tabog in Sweden, and New York.

92. Picromine.—2 Mg Si + H.

Rhombic, but massive. Cleavage, αP perfect; less so in other directions. Very sectile. H = 2½…3; G = 2½…2½. Translucent or opaque; vitreous, but nearly on αP. Greenish-white, gray, or blackish-green; streak colourless. Yields a bitter odour when breathed on (hence the name). In closed tube gives water and blackens. B.B. becomes white, and hard (= 5). Chem. com. 55-8 silica, 36-1 magnesium, and 8-1 water. Presnitz in Bohemia, and the Greiner in Tyrol.

Monoradite.—Massive, foliated, translucent, and yellowish-gray. H = 6; G = 3.267. Has nearly the same composition, but with half the water. B.B. infusible. Bergen, Norway.

Picrophyll.—Dark-green, foliated. G = 2½; H = 2½. B.B. infusible, but becoming white. Is also nearly related. Sala.

93. Villarsite.—2 Mg³⁺Si⁺ + H.

Rhombic; crystals αP P. P. 0P, with αP = 119° 59' (7); also granular. Fracture uneven. H = 3; G = 2½…3. Translucent. Greenish or grayish-yellow. B.B. infusible; decomposed by acids. Chem. com. 41 silica, 53 magnesia, with 34 iron protoxide and 23 manganese protoxide, and 6 water. Probably a pseudomorph of Olivine. Traversella in Piemont.

94. Spadaite.—Mg³⁺Si⁺ + 4 H.

Only massive, with splintery fracture. Sectile. H = 2½. Translucent; weak resinous. Red; streak white. B.B. fuses to an enamel-like glass; soluble in conc. h. acid, leaving slimy silica. Chem. com. 57 silica, 32 magnesia, and 11 water. Capo di Bove, near Rome.

95. Gymnite, Deweylite.—Mg³⁺Si⁺ + 5 H.

Only massive. H = 2½…3; G = 2½…2½. Semi-translucent; resinous. Pale or dirty orange-yellow. B.B. becomes dark-brown, and fuses on very thin edges. Chem. com. 42-1 silica, 37 magnesia, and 20-9 water. Bare Hills near Baltimore, and Tyrol.

96. Chonkrite.—3 (Mg, Ca, Fe)³⁺Si⁺ + Al + 2 H.

Massive. Fracture uneven. Sectile. H = 2½…3; G = 2½. Translucent; dull or glimmering. Snow, yellowish, or grayish-white. B.B. melts with ebullition to a grayish-white glass; soluble with deposition of silica in h. acid. Chem. com. 35-7 silica, 17-1 alumina, 22-5 magnesia, 12-6 lime, 1-5 iron protoxide, and 9 water. Elba.

97. Pyrosclerite.—3 Mg³⁺Si⁺ + Al + Si⁺ + 4 H.

Massive. Cleavage, in two directions at right angles, the one perfect, the other imperfect; fracture uneven, splintery. Sectile. H = 3; G = 2½…2½. Translucent; dull, or weak pearly. Apple, emerald, or grayish green. B.B. fuses with difficulty to a gray glass. With borax forms a chrome-green glass. The powder soluble in c. h. acid, leaving silica. Chem. com. 36-8 silica, 15-2 alumina (with 1-5 chrome-oxide), 33-7 magnesia, 3-5 iron protoxide, and 10-7 water. Elba, Aker in Södermanland.

98. Kambereite.—3 Mg³⁺Si⁺ + Al + Si⁺ + 5 H.

Hexagonal; OP, αP tabular and prismatic; but usually massive and foliated. Cleavage, basal perfect. Sectile; flexible. H = 1½…2; G = 2½. Translucent; pearly. Violet-blue, reddish, or greenish. Feels greasy. B.B. exfoliates without fusing. Chem. com. 37-0 silica, 14-2 alumina, 1-0 chrome-oxide, 31-5 magnesia, 1-5 lime, 1-5 iron protoxide, and 13-0 water. Bissersk in Siberia.

Rhodochrome.—Massive, fine scale, splintery fracture. H = 2½…3; G = 2½. Greenish-black, in fine splinters peach-blossom red. Tino in Greece, the Ural, Styria, and near Baltimore.

Tabergite, from Taberg; Vermiculite, in fine scales, twisting up, B.B., from Millbury, Mass.; and Loganite, from Canada, are closely allied.

99. Brucite, Nematite.—Mg H.

Rhombohedric; R. 82° 15'; crystals OR, αR; also foliated or columnar. Cleavage, basal very perfect. Sectile; fine laminae flexible. H = 2; G = 2½…2½. Translucent; pearly. Colourless, or grayish and greenish-white. B.B. infusible; easily soluble in acids. Chem. com. 69 magnesia, and 31 water, but after exposure often contains carbonic acid and effervescence. Nematite is the fine fibrous varieties with silky lustre. Swinanes in Unst, Hoboken in New Jersey, and Berezowsk in the Ural.

** Family IX.—Hornblende.**

Monoclinohedric mostly. Distinct cleavage in several directions. H = 4…6, but generally 5, or scratch with knife; G = 2½…4, but mostly high. Mostly coloured, ranging from white, through green (rarely brown), to black. Lustre sometimes silky or metallic pearly. Soluble, but not very readily, in acids; and more or less easily fusible. Chem. com. anhydrous silicates and aluminates of lime, magnesia, iron protoxide, more sparingly of soda, yttria, and manganese protoxide. The chief species are essential constituents of the igneous rocks, and form by their decomposition highly fertile soils.

N.B.—Hornblende and Augite rather represent groups of mineral substances than single species.

**100. Hornblende; f R³⁺Si⁺ = (Mg, Ca, Fe)³⁺(Si₂Al); or Amphibole.**

Monoclinohedric; C = 75° 10', αP 124° 30', P 148° 30'. The crystals short and thick, or long and thin prismatic, formed especially by αP (M) and (αP x) (x), and bounded on the ends chiefly by OP and P (r) (fig. 123). Macles common, with the chief axis the twin axis. Very often radiated, fibrous or columnar, or granular. Cleavage, prismatic along αP 124° 30' very perfect, orthodiagonal and clinodiagonal very imperfect. H = 5…6; G = 2½…3½. Pellucid in all degrees; vitreous, but sometimes pearly or silky. Colourless; often white, but usually some shade of gray, yellow, green, brown, or black. B.B. fuses, generally intumescing and boiling, to a gray, green, or black glass. Those containing most iron are most fusible, and are also partially soluble in hydrochloric acid, which scarcely affects the others. Chem. com. very variable, and hardly reducible to any general formula. Analyses range from 40 to 60 per cent. silica, 0 to 17 alumina, 0 to 30 lime, 0 to 36 iron protoxide (or peroxide), 0 to 4 manganese protoxide, 0 to 8 soda, 0 to 3 potash, and 0 to 1-5 fluorine, with a little water. The more remarkable varieties are—

1. Tremolite, Grammatite, or Colamite.—3 Mg³ Si⁴ + Ca² Si⁴ + Ca² Fe³, with 60-85 silica, 24-53 magnesia, 13-74 lime, and 0-88 fluoric acid. White, gray, green, rarely yellowish or blue; in long prismatic crystals, often bent and striated longitudinally. Pearly or silky; semitransparent or translucent. B.B. fuses readily to a white or nearly colourless glass. Lapland, Sweden, Arendal, Campo Longo, St Gotthardt, and other parts of the Alps; in the Pyrenees, Silesia, Siberia, North America; Glen Tilt, Glenelg, Tiree, and many parts of Scotland.

2. Actinolite, Actinote, or Strahlstein.—Colour green, inclining to black, gray, or brown. Translucent, or only on the edges. Long prismatic crystals, or radiated columnar masses. B.B. melts to a greenish or blackish enamel. Sweden, Tyrol, North America, Glenelg, Isle Oronsay, and Aberdeenshire.

3. Abestus, Amanthus, and Ryssolite.—Fine fibrous. White, gray, or green. The fibres often easily separable, elastic, and flexible. Savoy, Tyrol, and Corsica. Rock-cork, felt-like, and swims on water; Saxony, Sweden, Portsoy and Leadhills in Scotland. Rock-leather, flat and flexible; Leadhills, Aberdeenshire, and Strontian; and Rock-wood, near Sterzing in the Tyrol.

4. Anthophyllite.—Clove-brown to leek-green; translucent, radiating, and columnar; pearly on cleavage planes. B.B. very difficultly fusible. In it the lime is chiefly replaced by protoxide of iron. Kongsberg and near Brevig in Norway, Greenland, and the United States.

5. Hornblende.—Green or black, seldom brown or gray. G. = 3-3...4. B.B. fuses rather easily to a yellow, greenish, or black enamel. (Mg³ + Ca²) Si⁴ + Fe Al, with 47-9 silica, 13-2 alumina, 15-5 magnesia, 14-4 lime, and 9-0 iron protoxide in the black variety. Three varieties are distinguished.

(a.) The Noble or Pargasite, pale eladine or olive-green, and strong pearly or vitreous lustre; at Pargas in Finland, Tyre in Scotland. (b.) Common Hornblende, dark leek or blackish green, opaque; a constituent of many rocks, as in Norway, the Alps, and Scottish Highlands (Ben Lair, East Roma). Streak greenish-gray. (c.) Basaltic, velvet-black, foliated, opaque; streak gray or brown, in basalt and volcanic rock. Ural, Arendal, Bohemia.

Arefedonite.—3 Fe³ Si⁴ + Na² Si⁴, with 62-3 silica (2 alumina), 36-9 iron protoxide, 8-6 soda, and 2 lime. Pure black, opaque; streak grayish-green. Cleavage, very perfect along a prism of 123° 55'. G. = 3-44; H. = 6. Fusible in fine splinters in the flame of a candle. B.B. intumesces much, and melts to a black magnetic globule. Not soluble in acids. Greenland, Frederiksværn in Norway, and Arendal.

The Raphilitic, from Upper Canada, seems only tremolite.

Uralite.—Dark-green or greenish-black, with the outward form of augite, the internal structure and composition of hornblende. The Ural. Is probably a pseudomorph.

**101. Augite, Pyroxene.** (Ca² Si⁴ + (Mg, Fe)² Si⁴, or (Ca² Si⁴ + (Mg, Fe)³ Si⁴.

Fig. 125. Monoclinohedric; C. = 74°, P 87° 6', P 120° 39', —P

Fig. 126.

Mineralogy.

131° 29', 2P 96° 36'. Crystals, P (M), P (r), (P (r)) (P (s)), (fig. 125) P, 2P, OP, 3P, P, P, and P, (P (r)) (P (s)). P (r), almost always prismatic, imbedded, or attached; also granular, columnar, and scaly. Macles (fig. 126) common. Cleavage, prismatic along P (with angles of 87° 6' and 92° 54'), generally rather imperfect; orthodiagonal and clinodagonal imperfect. H. = 5...6; G. = 3-2...3-5. Pellucid in all degrees; vitreous; in some pearly on cleavage. Colourless, and white, but usually gray, green, or black. B.B. generally fusible; imperfectly soluble in acids. Chem. com. generally

| Silica | Lime | Magnesia | Iron | |-------|------|----------|------| | 60-96 | 25-46 | 18-18 | | | 52-72 | 23-31 | 8-50 | 14-27 | | 49-52 | 22-37 | | 28-11 |

Analysis gives 47 to 56 silica, 20 to 25 lime, 5 to 15 magnesia, 1 to 20 iron protoxide, with 0 to 3 manganese protoxide, and 0 to 8 alumina. The alumina, chiefly found in very dark green or black augites, may replace part of the silica.

The more important varieties are—

1. Diopside.—Grayish or greenish-white, to pearl-gray or leek-green; streak white. Crystalized or broad-columnar, or concentric lamellar. Transparent to translucent on the edges. Not affected by acids. B.B. fuses to a whitish semitransparent glass. Mussa Alpe (Musosite) and Ala (Alatile) in Piedmont, Swarzenstein in the Tyrol; also the Alps, Scandinavia, Finnland, Ural, and North America.

2. Sahltite, Matolcite.—Green, rarely yellow, brown or red; streak white. Translucent, or only on the edges; vitreous, inclining to pearly. Seldom crystallized (Baiklite), mostly columnar or lamellar. B.B. melts to a dark-coloured glass. Fassathal (Fassuite), Piedmont, Arendal, Philipstadt in Sweden; in the vicinity of Lake Baikal (Baiklite); near Lake Lherz in the Pyrenees (Lherzolite); Sahla, Sweden; Glentilt, Glenelg, Tiree, in Scotland; Tyrol, and North America. Coccolite is a distinct granular sahlite or augite.

3. Augite.—Leek-green, greenish-black, or velvet-black, rarely brown; streak greenish-gray. Vitreous to resinous; translucent or opaque. Only slightly affected by acids. B.B. fuses to a black, often magnetic glass. An essential component of many rocks, basalt, dolerite, clinestone, and augite porphyry, in Germany, Auvergne, Vesuvius, and in many parts of Scotland; associated chiefly with labradorite, also with olivine, leucite, or nepheline; rarely if ever with quartz.

4. Hedenbergite.—Black or blackish-green; opaque or translucent on the edges. B.B. melts to a black magnetic glass. Seems a lime-iron augite. Tunaberg, Jeffersonite, from Sparta, New Jersey; Hudsonite, from the Hudson River; and Polylite, are related.

5. Amanthus.—Some asbestiform minerals are probably augite, but the greater number are rather hornblende.

6. Breislackite.—Fine yellowish or brown woolly crystals. Vesuvius, and Capo di Bove near Rome.

Hornblende and augite agree so closely in crystalline forms and chemical composition, that it has sometimes been proposed to unite them in one species. They, however, differ too widely to justify their union. Thus, hornblende contains more silica, and a half to one per cent. of fluoric acid, which does not appear in augite. Hornblende, too, is more fusible, and ranges lower in specific gravity (hornblende from 2-931 to 3-445; augite, 3-195 to 3-525). Though both possess a cleavage parallel to their vertical prisms, yet these differ in angular dimensions. They also occur in distinct geognostic positions. Hornblende in rocks containing quartz or free silica, and mostly with minerals that are neutral compounds of silica, as orthoclase and albite; augite in rocks that do not contain free silica, and mostly with minerals that are not neutral silicates, as labradorite, olivine, and leucite. Hence there are two distinct series of massive or igneous rocks; the hornblende series, including granite, syenite, diorite, diorite-porphyry, and red porphyry; and the augite series or hypersthene rock, gabbro, dolerite, nepheline rock, augite-porphyry, and leucite-porphyry.

102. **NEPTUNITE**, Jade. \( \{2 \text{ Mg Si} + \text{Ca Si}, \text{or} \) \( \{3 \text{ Mg Si} + \text{Ca Si}. \)

Compact; fracture coarse splintery. Very tenacious. \( H = 6...6\frac{1}{2}; G = 2.9...3. \) Translucent, dull, or resinous. Leek-green, to greenish-white or blackish-green. Feels slightly greasy. B.B. become white and melt with difficulty to a gray mass. Chem. com. 57% silica, 24% magnesia, 17% lime; or 58% silica, 28% magnesia, and 13% lime, but with 1 to 3 protoxide of iron and 1 to 2.5 water. China and the East, also in New Zealand. Seem varieties of hornblende or augite. Cut into ring-stones or amulets.

103. **BOLTONITE**—(Mg, Fe, Ca) Si.

Granular; cleavage, one perfect, two others in traces. Translucent. Bluish-gray changing to yellowish-gray on exposure. B.B. infusible. Chem. com. 46 to 47 silica, 43 to 44 magnesia, 6 iron protoxide, and 3% lime. Bolton, Massachusetts.

104. **HYPERSTHENITE**, Paulite—(Mg, Fe) Si.

Isomorphous with augite, \( \alpha P 87°. \) Crystalline and granular, or disseminated. Cleavage, orthodiagonal very perfect, prismatic \( \alpha P \) distinct, clinodiagonal very imperfect. \( H = 6; G = 3.3...3.4. \) Opaque or translucent on thin edges; vitreous or resinous, but metallic pearly on the cleavage planes, of which one is copper-coloured, two silvery. Pinchbeck-brown, inclining to copper-red, pitch-black, and grayish-black; streak greenish-gray. Not affected by acids. B.B. melts more or less easily to a greenish-black glass, often magnetic. Chem. com. generally 46 to 58 silica, 0 to 4 alumina, 11 to 26 magnesia, 1 to 5 lime, 13 to 34 iron protoxide, 0 to 6 manganese protoxide. Paul's Island (Paulite), Labrador, and Greenland. Hypersthene rock in Norway, Effilj in Sweden, Skye and Ardnamurchan in Scotland. Also Cornwall; the Harz, and other parts of Germany.

*105. **BRONZITE**—(7 Mg + Fe) Si.

Monoclinohedric, like augite; \( C = 72°; \alpha P 86°; \) indistinct crystals or granular. Cleavage, orthodiagonal very perfect, \( \alpha P \) imperfect, clinodiagonal in traces. \( H = 4.5...5; G = 3.2...3.5. \) Translucent, or only on the edges; resinous or vitreous; on the more perfect cleavage planes, which are often slightly curved and fibrous; metallic-pearly or silky. Clove-brown to pinchbeck-brown, sometimes greenish or yellowish; streak white. Not affected by acids. B.B. very difficultly fusible to a dark-brown or blackish-green glass. Chem. com. 58% silica, 33% magnesia, and 8% iron protoxide; but also 1 to 2 alumina, 0 to 2.2 lime, and 0 to 3 manganese protoxide. Kraubat in Styria, Kupferberg in Baieruth, Ullenthal in Tyrol, and near Marburg.

*106. **DIALLAGE**—(Ca, Mg, Fe) Si.

Like augite, and only a variety, with very perfect cleavage in the clinodiagonal, a metallic-pearly lustre, and gray or pinchbeck-brown colour. B.B. melts easily to a grayish or greenish enamel. Chem. com. 50 to 53 silica, 1 to 5 alumina, 15 to 23 magnesia, 11 to 20 lime, and 5 to 12 manganese protoxide. Constituent of the Gabbro. Baste in the Harz, Silesia, the Alps, Apennines, and Ural. Vanadine-bronze, containing soda and vanadic acid, and Diaclasite, seem merely diallage.

107. **RHODONITE**, Manganese-spar—Mn Si.

Monoclinohedric, crystalline, or granular. Cleavage, \( \alpha P 87° 5' \) imperfect, \( (\alpha P \alpha) \) perfect, also \( \alpha P \beta \). Brittle. \( H = 5...5\frac{1}{2}; G = 3.5...3.6. \) Translucent; vitreous or partly pearly. Dark rose-red, bluish-red, or reddish-brown. Not affected by acids. B.B. fusible. Chem. com. 45-33 silica, and 53-67 manganese protoxide, with 3 to 5 lime, and 0 to 6 iron protoxide. Langhanshytta, Katharinenburg, the Harz, and New Jersey. The Bustamite, pale-greenish or reddish-gray, with 14 lime, Mexico; Fowlerite, New Jersey, with 7 to 11 iron protoxide, and Paisbergite, Sweden, are varieties. Hydropite, Photoite, Allagite, and Horn-manganese, mere mixtures.

108. **WOLLASTONITE**, Tabular-spar—Ca Si.

Monoclinohedric; \( C = 84° 40'; \alpha P 140°; \) or \( C = 69° 48'; \alpha P 87° 28'. \) Very rarely crystallized, mostly broad prismatic or lamellar. Cleavage, along \( OP \) and \( \alpha P \) perfect, but planes uneven or rough; meet at 95° 23'. \( H = 5; G = 2.7...2.9. \) Translucent; vitreous, or pearly on cleavage. White, inclining to gray, yellow, red, or brown; streak white. Phosphoresces with heat or friction; gelatinizes in hydrochloric acid. B.B. difficulty fusible to a semitransparent glass. Chem. com. 52% silica and 47% lime, but with 0 to 2 magnesia, and 0 to 2 iron protoxide. Bannat, Finland, Sweden, North America, Ceylon, Capo di Bove, Monaltrie in Aberdeenshire, and the Castle Rock at Edinburgh.

110. **ACRITE**—2 Fe Si + Na Si.

Monoclinohedric. Crystals long acute-pointed prisms. Cleavage like augite, \( \alpha P (86° 56'). \) \( H = 6...6\frac{1}{2}; G = 3.4...3.6. \) Nearly opaque; vitreous. Brownish or greenish-black; streak greenish-gray. Imperfectly soluble in acids. B.B. fuses easily to a black magnetic glass. Chem. com. 55% silica, 32 iron peroxide, and 12% soda, but with 1 to 3 manganese peroxide, and also 3 to 4 titanic acid. Eger and Porsgrund in Norway.

111. **BABINTONITE**—Rt Si, or Ca Si + 2 Fe Si.

Triclinohedric; \( \alpha P (M) = \alpha P (t) = 112° 30'; \alpha P (h) = \alpha P (g) = 90° 40'; OP (P) = \alpha P = 92° 34'; OP = 88° 0'. \) Crystals very low eight-sided prisms (fig. 127), small, attached. Cleavage, basal and brachydiagonal perfect. \( H = 5...5\frac{1}{2}; G = 3.4...3.5. \) Thin lamellate, transparent, greenish, and brownish. Splendent vitreous; black. Slowly soluble in boiling h. acid. B.B. fuses easily with effervescence to a black magnetic bead. Chem. com. 54% silica, 20% lime, and 25% iron protoxide, but with 0.3 to 6 alumina, 2.2 magnesia, and 2 to 10 manganese protoxide. Arendal, Zeland, and Governeur, New York.

112. **SORDALITE**—Al Si + 4 (Mg, Fe) Si + 2H.

Massive. Fracture conchoïdal; brittle. \( H = 4...4.5; G = 2.55...2.62. \) Opaque; resinous or vitreous. Brownish-black or blackish-green; streak liver-brown. B.B. fuses to a black globule. Chem. com. 50% silica, 12% phosphoric acid, 14 alumina, 19% iron protoxide, 10% magnesia, and 4% water. Sordalite in Finnland.

113. **KROKTIDOLITE**—3 Fe Si + (Na, Mg) Si + 2H.

Very fine, easily separable, but tough elastic fibres. \( H = 4; G = 3.2...3.3. \) Translucent; silky, or dull. Indigo blue; streak lavender-blue. B.B. fuses easily to a black magnetic glass. Chem. com. 50% silica, 35% iron protoxide, 2.2 magnesia, 6.7 soda, and 5% water. Orange River in South Africa, Stavern in Norway, and Greenland.

114. **PYRALLOLITE**.

Triclinohedric; prismatic; usually columnar or granular. Cleavage, \( \alpha P \) to \( \alpha P = 94° 36' \) distinct. Fracture uneven, splintery; rather brittle. \( H = 3.5...4; G = 2.55...2.60. \) Opaque, or translucent on the edges; resinous, or pearly. Greenish-white, asparagus-green, and yellowish-gray. B.B. becomes black, then white, and fuses with very much difficulty. Chem. com. silicate of magnesia with a little silicate of lime, water, and bituminous matter. Storgard, Finnland. Probably decomposed augite.

115. **ISOPYRE**—(Mg, Fe) Si + 3 Ca Si (?). Brittle; fracture conchoidal. H. = 5.5...6; G. = 2.90...2.95. Opaque; vitreous. Grayish or velvet-black, sometimes with red spots; streak pale greenish-gray. Imperfectly soluble in acids. B.B. fuses to a magnetic globule. Chem. com., by Turner's analysis, 47.09 silica, 13.91 alumina, 15.43 lime, 20.07 iron peroxide, 1.94 copper oxide. St Just near Penzance, Calton Hill, Edinburgh (7).

116. TACHYRITE.—Al₂Si₃ + 3(Fe, Ca, Mg, Mn, Na, K)Si. Conchoidal. H. = 6.5; G. = 2.52. Opaque; vitreous or resinous. Velvet, brownish, or greenish black; streak dark-gray. B.B. fuses very easily to an opaque glass; soluble in h. acid. Vogelsberg (Hyalomelan) near Dransfeld, Munden, and Iceland. Seems a vitreous basalt.

FAMILY X.—Clays.

Amorphous, earthy, variously-colored masses. H. = 1...5, but generally low or 1...3; G. = 1...3, but often about 2. Many have a shining streak, adhere to the tongue, feel greasy, and fall down in water. Some then form a ductile paste and are used for pottery. These are slightly affected by acids (under 25 per cent. of mass, soluble.) They are chiefly silicates of alumina, with about 10 to 12 per cent. water. Others with 20 to 25 per cent. water, and almost entirely soluble in acids, do not become plastic, and in the fire become misshapen or fuse; but often combine with grease or oil to an earthy soap. Many are thus of great economic importance. They rarely form true species, and are mostly indefinite mixtures or mere products of the decomposition of rocks and minerals.

*117. KAOLIN, Porcelain-earth.—Al₂Si₃ + 2 H₂O. Massive in beds and veins. Fracture uneven; fine-grained, very soft, sectile, and friable. H. = 1; G. = 2.2. Opaque, dull. White or gray, inclining to blue, green, yellow, or red. Feels meagre when dry, and plastic when wet. B.B. infusible. Not affected by h. acid, but decomposed by warm s. acid, leaving silica. Chem. com. very variable, but approximates to 47.2 silica, 39.1 alumina, and 13.7 water. Chiefly a product of the decomposition of orthoclase, or of granite, porphyry, and other rocks containing this mineral. Cornwall and Devonshire in Britain, Limoges in France, Meissen in Saxony, are the chief localities for the kaolin used in manufacturing porcelain.

*118. CLAY.

Clays are merely varieties of kaolin, mixed with quartz-sand, carbonate of lime, magnesia, the oxyhydrates of iron and manganese, or other substances. Generally they are compact and friable, of white, yellow, red, blue, gray, or brown colours. Their spec. gr. varies from 1.8 to 2.7. Varieties are: Pipe-clay, grayish or yellowish-white, with a greasy feel; adheres strongly to the tongue; and when wet is very plastic and tenacious, and in the fire burns white. Abundant in Devonshire, and in the Trough of Poole in Dorsetshire; in France, Belgium, and Germany. Used for manufacturing tobacco-pipes and similar articles. Potter's clay, red, yellow, green, or blue, becoming yellow or red when burnt; more easily fused than the former, and often effervesces with acids. That used in the potteries in England comes chiefly from Devonshire. Loom, coarser and more impure, with more sand, and consequently less plastic. Shale or Slate-clay, grayish-black, and much mixed with bituminous or carbonaceous matter. Bituminous shale, known by its shining, resinous streak. Black chalk, with more carbon, leaves a black mark on paper. Iron-clay contains much peroxide of iron, is reddish-brown, and forms the basis of many amygdaloids and porphyries.

119. ROCK-SOAP, Bergseife.

Compact. Fracture earthy or conchoidal; sectile. H. = 1...2. Streak resinous. Colour pitch-black and bluish-black. Feels very greasy; writes, but does not soil. Adheres strongly to the tongue, and falls to pieces in water.

Chem. com. 44 to 46 silica, 17 to 26 alumina, 6 to 10 iron peroxide, 13 to 25 water. Arnstedt, Cassel, Bilin, and Isle of Skye. Used for crayons by painters, and for washing cloth.

120. PLINTHITE.

Compact; earthy. H. = 2...3; G. = 2.34. Brick-red or brownish-red. Does not adhere to the tongue. B.B. becomes black, but is infusible. Chem. com. 30-9 silica, 20-8 alumina, 26.1 iron peroxide, 2.6 lime, and 10.6 water. Antrim in Ireland. Erinite, from the same place, is similar.

121. GREEN-EARTH.—Si, Al, Fe, Mg, K, H. Massive, forming crusts. Fracture, fine earthy; sectile. H. = 1...2; G. = 2.8. Opaque; streak shining. Green. Feels greasy. B.B. fuses to a black magnetic glass; not affected by acids. Common in the trap rocks of Faroe, Iceland, Scotland, and other countries; that used in the arts chiefly from Monte Baldo near Verona, and Cyprus. Glaucomite, small round green grains, in the greensand of England, France, Germany, and North America, is essentially a hydrous silicate of iron protoxide and potash, but, with 43 to 57 silica, 5 to 17 alumina, 19 to 27 iron protoxide, 5 to 15 potash, 1 to 4 magnesia, 0 to 3 lime, and 7 to 13 water. In New Jersey forms a valuable manure.

122. YELLOW-EARTH.—(Fe, Al)₂Si₃ + 4 H₂O. Fracture fine earthy or slaty. H. = 1...2; G. = 2.2. Ochre-yellow. Greasy; adheres slightly to the tongue, and pulverizes in water. B.B. infusible, but becomes red; partially soluble in h. acid. A mixture of silicate of alumina, peroxide of iron, and water. Harz, France, and Scotland. Used as a coarse pigment.

123. HALLOYSITE.—Al₂Si₃ + 4 H₂O. Reniform. H. = 1.5...2.5; G. = 1.9...2.1. Semitranslucent, and more so when moist. White, inclining to blue, green, or yellow. Adheres slightly to the tongue. B.B. infusible; soluble in c. s. acid. Chem. com. nearly 41.5 silica, 34.4 alumina, and 24.1 water. Liege, Tarnowitz, Thiviers in France; Eifel (Lenzinit); Scotland (Tuestite).

*124. FULLER'S-EARTH, Walkerde.

Fracture uneven, slaty, or earthy. H. = 1...1.5; G. = 1.8...2.0. Opaque; dull, but streak resinous. Green, gray, or white. Very greasy; scarcely adheres to the tongue. Falls down in water, but does not become plastic. That from Reigate in Surrey contained 53 silica, 10 alumina, 9.75 iron peroxide, 12.5 magnesia, 0.5 lime, and 24 water. It is used in preparing cloth,—the best for this purpose being found in England, as at Reigate, Maidstone in Kent, Woburn in Bedfordshire, &c.; also near Maxton in Scotland, in Saxony, Bohemia, and Styria.

125. ALLOPHANE.—Al₂Si₃ + 5 H₂O. Botryoidal and reniform. Fracture conchoidal, brittle. H. = 3; G. = 1.8...2. Pellucid; vitreous. Pale-blue, white, green, or brown. B.B. intumesces and becomes white, but does not fuse; gelatinizes in acids. Chem. com. often near 24.3 silica, 40.4 alumina, and 35.3 water; occasionally with 2 to 3 oxides of iron or copper and 2 to 4 carbonate of lime or magnesia. Charlton near Woolwich, Baden, Bonn, and Saal-field.

126. SCHÖNERTITE.—Al₂Si₃ + 20 H₂O. Amorphous. Conchoidal. H. = 3...3.5; G. = 2. Greenish, yellowish, or with brown spots. B.B. infusible, but burns white; gelatinizes in h. acid. Freienstein in Styria.

127. BOLE.

Earthy, in nests and veins. Conchoidal. H. = 1...2; G. = 2.2...2.5. Opaque, or translucent on the edges; dull resinous; streak shining. Brown, yellow, or red. Feels greasy; some adhere strongly to the tongue, others not at all. In water crackle and fall to pieces. B.B. harden, and generally fuse to an enamel; in acids are more or less soluble. Chem. com. hydrous silicates of alumina and iron peroxide in various proportions. Dransfield, Stolpen, Cler Mont, Auvergne, the trap rocks of the Hebrides and other parts of Scotland, and Ireland. Sinopite, red, from Asia Minor, is supposed to be the Sinopian earth of antiquity. Fettböl, from Freiberg, and Ochran, of a yellow colour, are infusible B.B.

128. Teratolite.

Fracture uneven, or earthy. H. = 2-3...3; G. = 2-5. Opaque; dull. Lavender-blue to plum-blue, often with reddish-white veins and spots. Feels rough and meagre. B.B. infusible. Schiller's analysis gave 4166 silica, 22-85 alumina, 12-98 iron peroxide, 3-04 lime, 2-55 magnesia, 0-93 potash, 1-68 manganese peroxide, 14-20 water (= 99-89). Planitz near Zwickau; the Terra miraculosa Saxoniae of old authors.

129. Kollywhite.—Al₂Si + 10H.

Fine-earthly. Fracture even or conchooidal. H. = 1...2; G. = 2-0...2-15. Semitranslucent or opaque; dull or glimmering. Snow-white, rarely reddish, greenish, or yellowish. Feels greasy, and adheres strongly to the tongue. B.B. infusible; gelatinizes imperfectly with acids. Chem. com. 14 silica, 46 alumina, and 40 water. Schemnitz, Pyrenees, and Saxony. Scarbroite, from Scarborough, is similar, but with more (48) water.

130. Lithomarge, Steinmark.

Kaolin substances; in general compact, earthy, or pseudomorphous. H. = 2-5...3-0; G. = 2-4...2-6. Opaque, or dimly translucent; dull. White, yellow, or red. Feel greasy, and adhere more or less to the tongue. Landshut, Clausthal, and the Harz. Similar are Carnat, fine red; and Myelin, pale yellow or red, and reniform; both from Rochlitz in Saxony; also Melospite, yellowish or greenish-white, from Neudeck in Bohemia.

131. Miloschin, Serbian.—(Al, Cr) Si + 3H.

Fracture conchoidal, or earthy. H. = 2; G. = 2-13. Indigo-blue to celadine-green. Adheres to the tongue, and cracks in water. B.B. infusible; partially soluble in h. acid. Contains 3-6 chrome oxide. Rudnaik in Servia.

132. Kerolite.—4MgSi + AlSi + 15H.

Reniform. Uneven, conchoidal, or splintery; rather brittle. H. = 2...3; G. = 2-3...2-4. Translucent; dull resinous. White, inclining to gray, yellow, green, or red. Feels greasy, but does not adhere to the tongue. B.B. infusible. Frankenstein in Silesia.

133. Agalmatolite, Figure—} 4AlSi + KSi + 3H.

Stone, Pagodite.

Massive or slaty. Fracture splintery; rather sectile. H. = 2...3; G. = 2-8...2-9. Translucent, or only on the edges; dull or glimmering. Green, gray, red, and yellow. Feels somewhat greasy, but does not adhere to the tongue. B.B. burns white and fuses slightly on very thin edges; soluble in warm s. acid. Chem. com. 55 silica, 33-1 alumina, 7-6 potash, and 4-4 water, with 0-5 to 3 iron peroxide, and 0 to 3 lime. China, where it is cut into various works of art; also Nagyrag in Hungary, and Saxony. Cimolite, pure white clay from Argentiera and Milo, used for cleaning cloth, is similar.

134. Soapstone, Saponite.—6MgSi + AlSi + 5H.

Massive; sectile and very soft. H. = 1-5; G. = 2-26. White, or light-gray, yellow, and reddish-brown; streak shining. Feels greasy, and writes feebly; does not adhere to the tongue. B.B. fuses to a colourless porous glass; soluble in s. acid. Chem. com. 50 silica, 11-8 alumina, 27-8 magnesia, and 10-4 water. Lizard Point and St. Clear in Cornwall, and Dalarme in Sweden (Piotie).

135. Onkosin.—2AlSi + (K, Mg)Si + 2H.

Fracture uneven or splintery; sectile. H. = 2; G. = 2-8. Translucent; slightly resinous. Apple-green or brown. B.B. intumesces and fuses; soluble in s. not in h. acid. Salzburg.

136. Pipestone.—(Al, Fe)Si + (Na, Ca, Mg)Si + H.

Compact; fracture earthy; sectile. H. = 1-5; G. = 2-6. Minera. Opaque, dull. Grayish-blue, black, or red (Cattinite). B.B. infusible. Used by the North American Indians for pipes.

137. Meerschaum.—2MgSi + 3H.

Fracture fine earthy; sectile. H. = 2...2-5; G. = 0-8...1-0 (when moist nearly 2). Opaque, dull. Streak slightly shining. Yellowish and grayish-white. Feels rather greasy, and adheres strongly to the tongue. B.B. contracts, becomes hard, and fuses on the edges; soluble in h. acid, leaving silica. Chem. com. 62-6 silica, 29-2 magnesia, and 9-1 water; but others give also 0-7 to 2-7 carbonic acid, and 14 hygroscopic water. Asia Minor, Greece, near Madrid and Toledo; Moravia and Wermeland (Aphrodite, G. = 2-21). Chiefly used in forming heads for tobacco pipes.

138. Pinellite.—(Ni, Mg)Si + H.

Fracture conchoidal. H. = 2-5; G. = 1-4 (Alizite)...2-3. Translucent; dull resinous. Colour apple-green; streak yellowish-white. Feels greasy. B.B. fuses to a slag only on thin edges. With borax shows reaction for nickel (32-65 nickel oxide). Silesia. Razoumoffskin is by some united to pinellite, but the variety from Kosemutz in Silesia contained no nickel.

139. Dermatin.—(Mg, Fe)Si + 2H.

Reniform. H. = 2-5; G. = 2-136. Resinous. Colour blackish-green; streak yellowish-white. Does not adhere to the tongue. B.B. cracks and becomes black. Waldheim in Saxony.

*Family XI.—Garnet.

Chiefly tesselar. H. = 6...7-5; G. = 3-1...3-8. All fusible and soluble in acids, but not readily, or only after ignition. Mostly highly coloured, and often with fine gemlike lustre; but rarely transparent, mostly translucent or opaque. Are mostly anhydrous silicates of alumina and the earths, coloured by oxides of iron, manganese, and chrome.

Occur imbedded, or in veins and druses, in the older crystalline rocks, but rarely as essential constituents.

**140. Garnet.—R₂Si₄ + 4H₂Si, or R₂Si₄ + 4H₂Si.

Tesselar; most common forms oO (fig. 3), and 202 (fig. 6). These are often combined (figs. 18 and 19). Also granular or compact. Cleavage dodecahedral, but very imperfect; fracture conchoidal, or uneven and splintery. H. = 6-5...7-5; G. = 3-5...4-3. Pellucid in all degrees; vitreous or resinous. Rarely colourless or white; generally red, brown, black, green, or yellow. B.B. in general fuse easily to a glass, black or gray, in those containing much iron, green or brown in the others, and often magnetic; imperfectly soluble in h. acid, some wholly, after long digestion, leaving the silica in powder. Chem. com. exceedingly variable, but generally form two series, according as R is chiefly alumina or chiefly iron peroxide; and these are again divided according as R is more especially lime, iron protoxide, magnesia, or similar bases.

The more important varieties are:

(1.) Almandine, or Noble Garnet.—Columbine-red inclining to violet, blood-red, or reddish-brown; streak white; transparent or translucent; sometimes magnetic. Is an iron-alumina garnet, Fe₃Si₄ + AlSi, with 37 silica, 20-1 alumina, and 42-9 iron protoxide. Common in the primary rocks, in crystals, or rarely forming beds and veins. The finest are from Pegu, Ceylon, and the East. Large crystals at Fabhun, Arendal, Kongsberg, the Tyrol, the Ural, and in North America. It is common in the mica-slates of Perth, Inverness, and Zetland; in granite at Rubislaw, Aberdeen. Used as an ornamental stone.

(2.) Manganese-alumina Garnet; R = Mn; reddish-brown; Spessart, Sweden. (3.) Lime-alumina Garnets.—Ca$^2$Si$^3$ + Al$^3$Si, with 40-7 silica, 22-5 alumina, and 36-8 lime. To these belong—

(a) Grossular.—White to olive-green, and translucent. Wilui River, Siberia, the Ural, and Telemark in Norway.

(b) Cinnamint-stone, Hessonite, or Kancellstein.—Hyacinth-red to honey or orange-yellow, and transparent or translucent. Ceylon and Vemeland. Romanezowite, Kimito in Finland, is similar. When polished, this variety is often named Hyacinth.

(c) Common Lime-garnet.—Red, brown, yellow, orange, and with part at least of the alumina replaced by iron peroxide. Abundant in Piedmont, Vesuvius, the Ural, and North America.

(4.) Magnesia-garnet.—R, chiefly magnesia; opaque, resinous; coal-black. G = 3-157. Arendal.

(5.) Iron-garnets.—Ca$^2$Si$^3$ + Fe$^3$Si, with 36-2 silica, 31-1 iron peroxide, and 33-6 lime. G = 3-7...4. More difficultly fusible and more easily soluble in h. acid than the others.

(a) Common Iron-garnet, Rothofsite, Allocroite.—Subtranslucent or opaque. Green, brown, yellow, or black, with white, gray, or yellow streak. Sweden and Arendal.

(b) Melanite.—Black; opaque; in thin splinters translucent. Streak gray; slightly magnetic. Albano near Frascati, Vesuvius, France, Lappmark. Pyreneites, near Bareges in the Pyrenees.

(c) Colophonite.—Yellowish-brown to pitch-black, also yellow or red; resinous; streak white. G = 3-43. Arendal.

(6.) Uvarovite, or Chrome-garnet.—Emerald-green; vitreous; streak greenish-white. Translucent or only on the edges. G = 3-4; H = 7-5. B.B. infusible. Bissersk and Kyschtinsk in the Ural.

141. Pyrope.—(Mg, Fe, Ca, Mn)$^3$Si$^3$ + Al$^3$Si.

Tesseral, but crystals (cubes) rare and indistinct; generally in roundish grains. Cleavage not perceptible; fracture conchoidal. H = 7-5; G = 3-7...3-8. Transparent or translucent; vitreous. Dark-hyacinth to blood-red. B.B. becomes black and opaque, but regains its colour and transparency on cooling; fuses with difficulty to a black glass; not soluble in acids, partially after fusion. Chem. com. 41-35 silica, 22-35 alumina, 15 magnesia, 9-94 iron protoxide, 5-29 lime, 4-17 chrome-protoxide, and 2-58 manganese-protoxide (Moberg). The chrome has also been considered as the oxide or acid. Zoblitz in Saxony, Meronitz and Mittelgebirge in Bohemia, and Ellie in Fife (Ellie rubies). Valued as a gem.

142. Helvine. $\{ \text{Mn S} + 3 \text{Fe}^2 \text{Si}, \text{or} \text{Mn S, Mn O} + (\text{Mn, Fe})^3 \text{Si}^3 + \text{Fe}^3 \text{Si}. \}$

Tesseral, and tetrahedral. $O_2$ or $O_2$. (fig. 128). Imbedded or attached. Cleavage, octahedral imperfect. H = 6...6-5; G = 3-1...3-3. Translucent on the edges; vitreous to resinous. Wax-yellow, siskin-green, or yellowish-brown. B.B. in the red flame fuses with intumescence to a yellow obscure pearl; soluble in h. acid, evolving sulphuretted hydrogen, and gelatinizes. Chem. com. 34 silica, 10 glaucia, 8 iron protoxide, 43 manganese protoxide, and 5 sulphur. Schwarzenberg in Saxony, and near Modum in Norway.

143. Idocrase.$\{ \text{(Ca, Mg, Fe)}^3 \text{Si}^3 + 2 \text{Al}^3 \text{Si}, \text{or Vesuvian}. \{ \text{(Ca, Mg, Fe)}^3 \text{Si}^3 + 2 \text{(Al, Fe)}^3 \text{Si}. \}$

Tetragonal; P 74° 27'. Crystals of $\alpha P$, $\alpha P$, $\alpha P$, P (56° 29'), $\alpha P$. Columnar; more rarely tabular or pyramidal (figs 129, 130). Also columnar or granular. Cleavage, prismatic along $\alpha P$ and $\alpha P$, but imperfect; fracture uneven, splintery. H = 6-5; G = 3-35...3-45 (or 4). Pellucid; vitreous or resinous. Yellow, green, brown, almost black; rarely azure-blue; streak white. B.B. fuses easily with intumescence to a yellowish-green or brown glass; partially soluble in h. acid, after fusion wholly, and gelatinizes. Chem. com. 39 silica, 22 alumina, 32 lime, 5 iron protoxide, and 2 magnesia. Vesuvius, Wilui River in Siberia, Massa-alp in Piedmont, Egg in Norway, Wicklow in Ireland, Monaltrie in Aberdeenshire, and near Bradford in Skye, in Scotland.

Gahuite, Lobote, Gokumite, from Gokum; Frugardite, from Finnland; Egeran, from near Eger; Cyprine, from Tellemark, Norway (azure-blue or green, contains copper, and B.B. melts easily in the inner flame to a red pearl); Xanthite, from Amity in New York—seem only idocrase.

Used as an ornamental stone, the brown being named hyacinth, the green chrysolite, but is not highly valued.

*144. Epidote.$\{ \text{(Ca, Mg, Fe)}^3 \text{Si}^3 + 2 \text{(Al, Fe, Mn)}^3 \text{Si}^3 \text{or R}^3 \text{Si}^3 + 2 \text{Fe}^3 \text{Si}. \}$ (Rams.)

Monoclinohedric; C = 89° 27', $\alpha P$ 63° 8', P 64° 36', $P \alpha$ 63° 43', P 70° 9'. P 70° 33'. Crystals horizontal-prismatic, as in fig. 131, where $\alpha P$ ($M$), $P \alpha$ ($T$), $P \alpha$ ($r$) — $P$ ($a$). Generally in druses; the surface often horizontally striated. Macles united by a face of $P \alpha$; also columnar, granular, or compact. Cleavage, orthodiagonal very perfect, along $P \alpha$ rather perfect. Fracture conchoidal, uneven, or splintery. H = 6...7; G = 3-2...3-5. Pellucid in all degrees; vitreous, on cleavage adamantine. Especially green, yellow, and gray; rarely red and black. B.B. fusible; strongly ignited, or after fusion all are soluble in h. acid, and gelatinize. Varieties are—

(1.) Zoisite.—White, yellowish, or brownish-gray; chiefly large imbedded crystals, or foliated and columnar. B.B. intumesces and forms a white or yellow porous mass, and on the edges fuses to a clear glass. Is a lime-alumina epidote, = 42-4 silica, 31-4 alumina, 26-2 lime, with very little iron oxide or magnesia. San Alpe in Carinthia, the Ural, and Connecticut. Thulite, rose or peach-blossom red, from Sonland in Norway, is similar.

(2.) Pistazite, Thallite.—Pistacio-green to blackish-green and black, also yellow or brown. Crystallized, granular, or earthy, also in crusts. B.B. fuses on the edges, and swells into a dark-brown slag. Is an iron-epidote, with 10 to 16 peroxide and 2 to 6 protoxide of iron. Arendal, the Ural, the Alps (Mont Blanc), Pyrenees, the Harz, Finnland, Greenland, and North America. In Scotland, in syenite in Zetland, in gneiss in Sutherland, in trap in Mull and Skye, in quartz in Rona, in clay-slate in Arran, and in porphyry in Arran and Glencoe. Puschkinite, from the Ural, Withamite, from Glencoe, in minute bright-red crystals; and Bucklandite, in small black crystals, from Lake Laach and Siberia, are this variety.

(3.) Manganese-epidote.—With much manganese-peroxide (14 to 20). Dark violet-blue or reddish-black; streak cherry-red. H = 6-5; G = 3-4. B.B. melts easily to a black glass. St Marcel in Piedmont. **145. AXINITE.**

\[ (2 \text{Ca, Mg})^2 \text{Si}^3 + 3 (\text{Al, Fe, Mn}) \text{Si} + (\text{Ca, Mg}) \text{B}, \text{or} \\ 2 [\text{Fe Si} + \text{R' Si}] + \text{B Si}. \]

Triclinohedric. Crystals usually very unsymmetrical (figs. 132 and 133), with \( u = P = 135^\circ 24', u = r = 115^\circ 39' \).

\( P \) to \( r = 134^\circ 48' \); attached singly, or in druses. Also laminar or broadly radiated. Cleavage, imperfect along a plane truncating the sharp edge between \( P \) and \( u \). \( H = 6 \ldots 7; G = 3 \ldots 3-3 \). Pellucid; vitreous. Clove-brown, inclining to smoke-gray or plum-blue, but often cinnamon-brown in one direction, dark violet-blue in a second, and pale olive-green in a third. B.B. intumesces and fuses easily to a dark-green glass, becoming black in the ox. flame; not soluble in h. acid till after ignition, when it gelatinizes. Chem. com. about 44 silica, 5 boracic acid, 16 alumina, 11 iron peroxide, 1-5 manganese-peroxide, 2-5 magnesia, and 20 lime. Bourg d'Oisans in Dauphine, and the Botallack mine in Cornwall, Kongsberg in Norway, Arendal, Nordmark in Sweden, Pyrenees, Savoy, Tyrol, Thun in Saxony (Thummerstein), the Ural, and North America.

**146. GLAUCOPHANE.**

\[ (2 \text{Al Si}^3 + 9 (\text{Fe, Na, Mg, Ca}) \text{Si} \]

Rhombic or monoclinohedric, only indistinct; thin four or six-sided prismatic crystals, or granular. Cleavage, prismatic distinct; fracture conchoidal. \( H = 5 \ldots 5; G = 3 \ldots 3 \). Translucent or opaque; vitreous or pearly. Gray, indigo-blue, or bluish-black. B.B. becomes yellowish-brown, and fuses readily to an olive-green glass; partly soluble in acids. Island of Syra. Similar are—

Wichtyne.—Massive; black. B.B. fuses to a black enamel; not affected by acids. Wichtis in Finnland. Violan.—Massive; opaque, resinous. Dark violet-blue. B.B. fuses easily to a clear glass. St Marcel in Piedmont.

**FAMILY XII.—CYANITE.**

Triclinohedric or rhombic, often in long prismatic forms. \( H = 5 \ldots 7-5; G = 2-9 \ldots 3-8 \). B.B. infusible; insoluble in acids. Some show fine colours and high vitreous lustre. They are chiefly anhydrous silicates of alumina. Occur especially in the crystalline strata.

**147. CYANITE, Disthenite.**

\[ \text{Al Si}, \text{or Al}^3 \text{Si} \]

Triclinohedric. Generally broad prismatic lengthened crystals formed by two faces meeting at 106° 16'. Macles are common, united by \( \alpha P \). Also even, curved, or radiated. Cleavage, along the prisms very (or less) perfect; brittle. \( H = 5 \) on cleavage planes, on other faces \( = 7; G = 3 \ldots 5 \) to 3-7. Pellucid, vitreous; on cleavage pearly. Colourless, or blue, gray, green, yellow, or red. Not affected by acids. B.B. infusible. Chem. com. 37-6 silica, and 62-4 alumina. St Gotthardt, Tyrol (Rhaetizite), Pontivy in France, Bohemia, Nigg near Aberdeen, Botriphny in Banffshire, and Hillswick in Zetland.

**148. SILLIMANTITE.**

\[ \text{Al Si} \]

Triclinohedric, with \( \alpha P = \alpha P' = 98^\circ; P' = \alpha P' = 105^\circ \). Crystals long and slender; also fibrous or parallel. Cleavage, macrodiagonal highly perfect. \( H = 7 \ldots 7-5; G = 3 \ldots 2 \ldots 3-26 \). Translucent; vitreous, inclining to pearly. Grayish-brown, clove, or hair-brown. B.B. infusible; not affected by acids. Chem. com. like cyanite, from which it is scarcely distinct. Chester and Norwich in Connecticut, Tvedestrand in Norway. The Xenolite, Finnland; Bucholzite, Fibrolite, and Bamlite, from Bamle in Norway, seem also cyanite; Worthite, an altered variety.

**149. ANDALUSITE.**

\[ \text{Al Si}, \text{or Al}^3 \text{Si} = \text{Al}^3 \text{Si} \]

Rhombic; \( \alpha P = 90^\circ 44'; P = 109^\circ 6' \). Crystals \( \alpha P \cdot OP \), or this with \( P \) (fig. 135); prismatic, attached or imbedded; also columnar, or granular. Cleavage, \( \alpha P \) rather indistinct; traces along \( \alpha P \), \( \alpha P \) and \( P \). Fracture uneven, splintery. \( H = 7 \ldots 7-5; G = 3 \ldots 3-3 \). Pellucid; vitreous. Gray, green, red, or blue. B.B. infusible; not affected by acids. Chem. com. 40-4 silica and 59-6 alumina, with 1 to 2 iron peroxide. Andalusia, Lisens in Tyrol, Penig in Saxony, Westford in Massachusetts, Litchfield in Connecticut; and Botriphny in Banffshire, Tyrie in Aberdeenshire, and Killiney Bay in Wicklow.

Chiolosite.—\( H = 5 \ldots 5-5; G = 3 \). Dirty or pale gray, yellow, or red. Occurs imbedded in clay-slate, and often appears like four crystals separated by a black cross (fig. 136). Fichtelgebirge, Brittany, the Pyrenees, Sierra Morena, Wollsrag near Keswick, and on Skiddaw in Cumberland; near Balahulish in Argyleshire, Boharm in Banffshire, and in Wicklow.

**150. STAUROLITE, Staurotide.**

\[ (\text{Al, Fe})^3 \text{Si} = \text{Fe}^3 \text{Si}, \text{or} \\ (\text{Al, Fe})^3 \text{Si} \]

Rhombic; \( \alpha P = 128^\circ 42'; P = 70^\circ 46' \). Crystals \( \alpha P (M) \), \( \alpha P (o) \cdot OP (p) \). Macles very common, like figs. 137 or 138. Cleavage, brachydiagonal perfect, traces along \( \alpha P \); fracture conchoidal, or uneven and splintery. \( H = 7; G = 3 \ldots 3-8 \). Translucent or opaque; vitreous, inclining to resinous. Reddish to blackish-brown; streak white. B.B. infusible; not affected by h. partially by s. acid. Chem. com. ranges from 28 to 40 silica, 45 to 55 alumina, 15 to 18 iron peroxide, with 0-2 to 2-5 magnesia. St Gotthardt and Greiner in Tyrol, Finisterre, Pyrenees, Spain, the Ural, and in North America; in Scotland, Bixeter Voe in Zetland, in Aberdeenshire, and the Hebrides.

**151. DIASPORE.**

\[ \text{Al H} \]

Rhombic; \( \alpha P = 130^\circ \), broad indistinct prisms, chiefly of \( \alpha P \), bounded by the curved faces of \( P \) (fig. 139). Usually thin foliated or broad radiated. Cleavage, brachydiagonal highly perfect; very brittle. \( H = 6; G = 3 \ldots 3-3 \). Pellucid; vitreous; pearly on \( \alpha P \). Colourless, but generally yellowish or greenish-white; also violet-blue. Insoluble in acids. B.B. infusible, but some decrepitate into small white scales. Chem. com. 85 alumina and 15 water. Rare. Ural and Schenitz, Broddbo and St Gotthard.

**152. HYDRARGILITE.**

Hexagonal; \( OP = \alpha P = \alpha P2 \), or granular scaly. Cleavage, basal very perfect. \( H = 2-5 \ldots 3; G = 2-3 \ldots 2-4 \). Translucent; vitreous; pearly on \( OP \). Colourless or reddish-white. Slowly soluble in warm acids. B.B. exfoliates, and gives out a strong light, but is infusible. Chem. com. 65-3 alumina and 34-5 water. Near Slatoust in the Ural. Stalacitic, greenish or grayish-white (Gibbsite); Richmond, Massachusetts, Villa Rica in Brazil.

153. Periclase.—Mg.

Tesseral, only in octahedrons. Cleavage, hexahedral perfect. H. = 6; G. = 3·75. Transparent; vitreous. Dark-green. B.B. infusible; powder soluble in acids. Chem. com. magnesia, with 5 to 8 protoxide of iron. Monte Somma.

FAMILY XIII.—Gems.

All very hard, H. = 7...9, or scratch quartz, except a few = 6 which are scarcely true gems; G. = 2·6...4·7, but mostly high in the finest. Insoluble in acids, and infusible B.B. in the true gems. These have a high lustre, brilliant colours, and take a fine polish, and are therefore much valued. They are, however, rare, and generally small. Chem. com. variable, but mostly simple. Chiefly occur in the older igneous or metamorphic rocks.

*154. Zircon.—Zr Si, or Zr Si, or Zr Si.

Tetragonal; P 84° 20'. Crystals, often P-P, often with 3 P; also P-P, P, or P-P (s), P (t), P (P), P-P (x), P-P (y), P-P (z) (fig. 140), chiefly prismatic or pyramidal, and in rounded grains. Cleavage, along P and P, both rather imperfect; fracture conchoidal or uneven. H. = 7·5; G. = 2·4·7. Transparent to opaque; vitreous, often adamantine. Rarely white, generally gray, yellow, green, or frequently red and brown. B.B. loses its colour, but is infusible; not affected by any acid except conc. s. acid, after long digestion. Chem. com. 66-23 zirconia (and norite, Stenbergs), and 33-77 silica, with 0 to 2 iron peroxide as colouring matter. Southern Norway, Ilmen Mountains, Arendal, Sweden, Carinthia, Tyrol, Ceylon, and North America; in Scotland, at Scalpay in Harris, and Criffel.

The colourless varieties are often sold for diamonds. The more brilliantly coloured are named hyacinth.

155. Malakon.—3 Zr Si + H.

Tetragonal; P. 82°. Crystals, like zircon. H. = 6; G. = 3·9. Opaque; resinous or vitreous. Internally bluish-white, but on the surface mostly brownish, reddish, yellowish, or blackish. Chem. com. zircon, with 3 per cent. water. Hitterö in Norway, Malakon. Cerestlite from Arendal, Tachyphallite from Krageroe, and Calypotite, are probably altered zircon.

*156. Spinel.—Mg Al, or (Mg, Fe) (Al, Fe).

Tesseral; O alone or predominating, P-O and 3O3. Macles common, united by a face of O (fig. 141); also in grains or fragments. Cleavage, octahedral imperfect; fracture conchoidal. H. = 8; G. = 3·4...3·8. Transparent to opaque; vitreous. Red, blue, green, and black; streak white. B.B. infusible and unchanged. Chem. com. 71 alumina and 29 magnesia; but some 1 to 5 silica, 3 to 20 iron protoxide, 0 to 6 iron peroxide, and the red varieties 1 to 5 chrome. The varieties are:

Spinel or Spinel-ruby, rose-red (Balas ruby), yellow or orange-red (Rubicelle), violet (Almandine ruby) or brown; G. = 3·52; from Ceylon, Ava, and the East. Much prized as ornamental stones. Sapphire.—Pale sapphire-blue to greenish or reddish blue; G. = 3·4...3·7; with 4 per cent. iron protoxide; Aker in Sweden, Greenland, North America. Pleonaste, opaque or translucent, black; G. = 3·65...3·8; with 8 to 20 iron protoxide; Candy in Ceylon (Candite, or Zeilanite), Monte Somma, Monzoni, Arendal, Bohemia (Hercinite), the Ural, and New York. Chlorospinel, grass-green, with a yellowish-white streak; G. = 3·59; Slatoust in the Ural.

157. Autunite, Galnite.—Zn Al.

Tesseral; O, alone or macleled. Cleavage, O perfect; brittle, with conchoidal or splintery fracture. H. = 8; G. = 4·3...4·6. Opaque or translucent on the edges; vitreous, inclining to resinous. Dark lead-green to blackish-green and blue; streak gray. B.B. unchanged; not affected by acids or alkalis. Chem. com. 56 alumina and 44 zinc oxide, but with 1 to 6 protoxide of iron, and 2 to 5 magnesia. Fahlun, Brodöbo, Haddam in Connecticut, and Franklin in New Jersey. Dyselite, yellowish-brown, with manganese, from Sterling, Massachusetts; and Kreittonite, brown, from Bodenmais, are similar.

*158. Corundum.—Al.

Rhombohedral; isomorphous with protoxide of iron and chrome; R 86° 4'. Crystals chiefly of P2 (s), OR (o), R (P), are pyramidal (fig. 142), prismatic (fig. 143), or rhombohedral. Macles common, united by a face of R. Cleavage, rhombohedral along R, or basal. Extremely tough, and difficultly frangible. H. = 9; G. = 3·9...4·2. Transparent or translucent; vitreous, or pearly on OR. Colourless and white, but generally blue, red, yellow, brown, or gray. B.B. unchanged. Chem. com. alumina, with a minute proportion of protoxide of iron or other colouring matter.

Varieties are:—(1.) Sapphire, highly transparent, very imperfect cleavage and conchoidal fracture; colourless, blue (Salamstein), seldom green, yellow, red (Oriental rubies), or brown; Ceylon, Ava, Pegu, Misk, Slatoust, Bilin in Bohemia, and Exailla in Auvergne. (2.) Corundum, rough crystals or foliated, less transparent and duller colours; Malabar, Ceylon, Ava, Canton in China, Siberia, St Gotthard, and Piedmont. Some (Asteria or star sapphire) show a bright opalescent star of six rays. (3.) Adamantine spar, with distinct cleavage, hair-brown, and adamantine; Gellivara, Ural, Malabar, and North America. (4.) Emery, compact, dimly translucent, and gray or indigo-blue; Asia Minor near Smyrna, Naxos, Spain, Saxony, and Greenland. Sapphire and rubies are highly valued as ornamental stones; emery as a polishing material.

159. Chrysoberyl, Cynophane.

Rhombic; P with polar edges 86° 16' and 139° 53'. Crystals of P-P (M), P-P (T), P-P (o), or this with P-P (q), and also with P (o) (fig. 144), are short and broadly columnar, or thick tabular with vertical strike. Macles very common, united by a face of P-P. Cleavage, brachydiagonal imperfect, macrodiagonal more so; fracture conchoidal. H. = 8.5; G. = 3.69...3.8. Transparent or translucent; vitreous, sometimes resinous. Greenish-white, leek-green, olive-green, and greenish-gray; sometimes with a bluish opalescence, or beautiful dichroism. B.B. infusible; not affected by acids. Chem. com. 80.25 alumina and 19.75 glaucia, with 3 to 4 protoxide of iron. Brazil, Ceylon, India, Haddam in Connecticut, and Ural.

*160. TOPAZ. \( \frac{6}{\text{Al}} \text{Si} + (\text{Al F}^3 + \text{Si F}^3) \), or \( \frac{6}{\text{Al}} \text{Si}^3 + (3 \text{Al F}^3 + 2 \text{Si F}^3) \).

Rhombic; \( \alpha P(M) 124° 19', 2P(\alpha) 93°, \alpha P2(l) 93° 8', P(o) \), and numerous other forms. Crystals always prismatic (fig. 145), often hemimorphic, and the prisms finely striated; also granular. Cleavage, basal very perfect, traces in other directions, especially M and I in the Scottish varieties; fracture conchoidal or uneven. H. = 8; G. = 3.4...3.6. Transparent to translucent on the edges; vitreous. Colourless, but yellowish, reddish, or greenish-white, honey-yellow, hyacinth-red, violet-blue, and asparagus-green. Becomes electric from heat or friction. B.B. infusible. Not affected by h. acid, but by long digestion in s. acid gives traces of fluorine. Chem. com. 35.52 silica, 53.33 alumina, and 17.49 fluorine (= 108.33). Brazil, Siberia, Ceylon, New Holland, Peru, Connecticut, Bohemia, Saxony, and Cornwall (St Michael's Mount), Mourne Mountains in Ireland, Cairngorm Mountains in Aberdeenshire (one crystal nineteen ounces). The common or coarse columnar named Pyrophylite, at Finbo, and Broddbo near Falun. Topaz is valued as an ornamental stone. The purest from Brazil, when cut in facets like the diamond, closely resemble it in lustre and brilliance, and are easily known by their electricity.

161. PYCNITE, Schorlute. \( \frac{3}{\text{Ca}} \text{Si} + (\text{Al F}^3 + \text{Si F}^3) \).

Massive; like topaz. H. = 7.5; G. = 3.49...3.54. Translucent; vitreous. Straw-yellow to reddish-white. Chem. com. 39.04 silica, 51.25 alumina, 18.48 fluorine. Altenberg in Saxony, and Schlackenwald and Zinnwald in Bohemia.

162. LEUCOPHANE. \( \frac{3}{\text{Ca}} \text{Si} + \text{Ca F} \).

Triclinohedric; but crystals rare. Cleavage in three directions, intersecting at 53° 25' and 65°. H. = 3.5...4; G. = 2.974. In thin splinters pellucid and almost colourless; in thicker pieces wine-yellow or olive-green; vitreous or resinous. B.B. fuses to a pale violet-blue bead. Near Breivig in Norway.

163. EUCLASE. \( \frac{3}{\text{Al}} \text{Si} + \text{Ca F} \).

Monoclinohedric; C. = 71° 7'; \( \alpha P 115°, P 105° 49' \). Crystals \( \alpha P(s), (\alpha P \infty)(T), P(f) \) (fig. 146). Cleavage, clinodiagonal highly perfect, along \( P \infty \) less so; \( \alpha P \infty \) in traces. Very brittle and fragile; fracture conchoidal. H. = 7.5; G. = 3...3.1. Transparent; splendid vitreous. Pale mountain-green, passing into yellow, blue, or white. B.B. intumesces, becomes white, and melts in thin splinters to a white enamel. Not affected by acids. Chem. com. 44.7 silica, 31.8 alumina, and 23.5 glaucia, with 1 to 2.2 iron protoxide and 0.4 to 0.7 tin oxide. Peru and Brazil, but very rare.

*164. EMERALD, BERYL. \( \frac{4}{\text{Al}} \text{Si}^3 + \text{Ca Si}^3 \), or \( \frac{4}{\text{Al}} \text{Si}^3 + \text{Ca Si}^3 \).

Hexagonal; \( P 59° 53' \). Crystals of \( \alpha P, OP, \) and \( \alpha P \infty P2 \) (fig. 147), are prismatic, generally with vertical striæ. Cleavage, basal rather perfect, \( \alpha P \) imperfect. H. = 7.5...8; G. = 2.6...2.8. Transparent or translucent; vitreous. Colourless or white, but generally green, sometimes very brilliant, also yellow, and smalt-blue. B.B. melts with difficulty on the edges to an obscure vesicular glass. Not affected by acids. Chem. com. 67.9 silica, 18.7 alumina, and 13.8 glaucia, with 0.3 to 3 iron protoxide, and 0.3 to 3.5 chrome oxide in the rich green emerald. Emerald, bright green; G. = 2.710...2.759; occurs in Muso Valley near Bogota, also in Salzburg and the Ural. Beryl, or Aquamarine, colourless, or less brilliant; G. = 2.577...2.725; near Murinsk, and Nertschinsk in Siberia, Salzburg and Brazil; in the United States, at Ackworth in New Hampshire, Royalston in Massachusetts, Haddam in Connecticut; Mourne Mountains in Ireland, and Cairngorm Mountains in Aberdeenshire. Common beryl at Falun in Sweden, Possum in Norway, Limoges in France, Rabenstein in Bavaria, Rubishaw near Aberdeen (Davidsonite). Emerald and beryl are much valued as precious stones.

165. PHENAKITE. \( \frac{3}{\text{Al}} \text{Si}^3 \).

Rhombohedric; R 116° 40'. Crystals R. \( \alpha P2, \alpha P2, \frac{3}{\text{P2}} \) (fig. 148). Macles with parallel axes and intersecting. Cleavage, R and \( \alpha P2 \) not very distinct; fracture conchoidal. H. = 7.5...8; G. = 2.97. Transparent or translucent; vitreous. Colourless, and wine-yellow or brown. B.B. infusible; not affected by acids. Chem. com. 55 silica, and 45 glaucia. Ural, Ilmen Mountains, Framont in Alsace.

*166. CORDIERITE, Iolite, \( \frac{3}{\text{Al}} \text{Si}^3 + 2(\text{Mg, Fe}) \text{Si} \), or Dichroite. \( \frac{3}{\text{Al}} \text{Si}^3 + \text{Rb} \text{Si} \).

Rhombic; \( \alpha P 119° 10', \) middle edge of \( P 95° 36' \). Crystals \( \alpha P(T), \alpha P \infty(T), OP(M), \) and this with \( \alpha P \infty(k), \alpha P3(d), P \infty(n), \) and \( \frac{3}{\text{P2}}(e) \) (fig. 149); short, prismatic. Cleavage, \( \alpha P \infty \) rather distinct, traces along \( P \infty \); fracture conchoidal or uneven. H. = 7...7.5; G. = 2.5...2.7. Transparent or translucent; vitreous, inclining to resinous. Colourless, but chiefly blue, green, brown, yellow, and gray, often with distinct pleochroism. B.B. fuses slowly to a clear glass; slightly affected by acids. Chem. com. 48 to 51 silica, 29 to 33 alumina, 8 to 13 magnesia, 1 to 12 iron protoxide, and 0 to 1.5 manganese protoxide. Cabo de Gata in Spain, Bodenmais (Pelion), Orrijervi (Steinheilite), Norway, Sweden, Greenland, North America, and Siberia. Small rolled masses of an intense blue colour and transparent, found in Ceylon, are the Sapphire d'Eau or Luchssapphire of the jewellers.

The following substances seem cordierite altered, or with 2 to 4 atoms water:

(a) Bondorfite, Hydrous Iolite, greenish-brown, or dark olive-green, near Åbo. (b) Esmarkite, Chlorophyl- lite, large prisms or foliated, green or brownish; near Brevig in Norway, Unity in Maine, and Haddam in Connecticut.

(c.) Fahlunite, Triclastic, compact, greenish-brown or black foliated; $H = 2\frac{5}{6}...3$; $G = 2\frac{5}{6}...2\frac{8}{9}$; Fahlun.

(d.) Weissite, kidney-shaped and ash-gray or brown; Fahlun and Lower Canada.

(e.) Pyrrhellite, indistinct imbedded crystals, black passing into brown or red, dull resinous lustre; $H = 3\frac{5}{6}$; $G = 2\frac{5}{6}$; Helsingfors.

(f.) Pinite, crystallized, or massive and laminar, with imperfect cleavage; $H = 2...3$; $G = 2\frac{7}{8}...2\frac{9}{10}$; semitranslucent or opaque, dull or resinous, and dirty-gray, green, or brown; B.B. fuses to a glass, sometimes clear, at other times dark-colored; Auvergne, Schneeberg, Penig in Saxony, in the Harz, Cornwall, Aberdeenshire, the United States, and Greenland (Giesekite).

Oositite from Geroldseck in Baden, snow-white, opaque, fragile, is similar.

(g.) Gigantolite; $H = 3\frac{5}{6}$; $G = 2\frac{8}{9}...2\frac{9}{10}$; opaque, dull resinous, and greenish-gray or brown; B.B. intumesces slightly, and fuses easily to a greenish slag; Tammela in Finnland.

(h.) Praseolite, lamellar and green; Brevig in Norway.

**167. Tourmaline, Schorl.**

Rhombohedric; $R = 133^\circ 10'$. Crystals of OR ($K$), $\frac{1}{4}R$ ($155^\circ$) ($m$), $R(P)$, $-2R$ ($103^\circ 3'$) ($o$), $\alpha PZ$ ($s$), and $\omega R$ ($t$), usually long prismatic, striated, and remarkable for hemimorphism, $\alpha R$ appearing as a trigonal prism (figs. 150, 151); also radiating, columnar, or fibrous. Cleavage, $R$ and $\alpha P$ both imperfect; fracture conchoidal or uneven. $H = 6\frac{5}{6}...7\frac{5}{6}$; $G = 3...3\frac{3}{4}$. The black opaque, the others pellucid; vitreous. Colourless, but gray, yellow, green, blue, red, brown, and most frequently black. Often several colours in layers perpendicular, or parallel to the axis. By friction acquires positive, by heat polar electricity; powder white, often magnetic. B.B. some fuse, others only intumesce, and some both fuse and intumesce. Powder not soluble in h., only imperfectly in s. acid. Chem. com. very complex, with 36 to 41 silica, 5 to 10 boracic acid, 13 to 27 fluorine, 0 to 0.3 phosphoric acid, 30 to 48 alumina, 0 to 13 iron peroxide, 0 to 5 manganese peroxide, 0 to 10 iron protoxide, 0.5 to 15 magnesia, 0 to 2 lime, 1 to 2.6 soda, 0.1 to 2 potash, and 0 to 1.5 lithia. Rammelsberg makes five groups in two divisions:

A. Tourmalines with no lithia, and little or no manganese:

(1.) Magnesia Tourm. — $R^2 \text{Si}^3 + 3R^2 \text{Si};$ yellow and brown, with much magnesia and little iron.

(2.) Magnesia-iron T. — $R^2 \text{Si}^3 + 4R^2 \text{Si};$ apparently black; with an average amount of magnesia and iron.

(3.) Iron T. — $R^2 \text{Si}^3 + 6R^2 \text{Si};$ deep black with most iron and least magnesia.

B. Tourmalines with lithia and little magnesia:

(4.) Iron-manganese T. — $R^2 \text{Si}^3 + 3R^2 \text{Si};$ blue (or violet) and green T., with iron.

(5.) Manganese T. — $R^2 \text{Si}^3 + 4R^2 \text{Si};$ red or colourless, with no iron.

Groups 2 and 3 are the most common, and known as Mineralogy, the red varieties as Rubellite, the colourless as Adroite.

The finest transparent varieties or noble tourmalines come from Ceylon, Siberia, and Brazil. The dark-blue or Indicolite occurs chiefly in Utoe. Large crystals of the dark opaque varieties occur in Greenland, Arendal, the Tyrol, and various parts of North America. In England, Bovey in Devonshire and St Just in Cornwall, are well-known localities; and in Scotland large prisms, often curved or broken, abound in the granite of Aberdeenshire.

Tourmaline is not much valued as a gem, the colours being rarely pure. Zeuzite seems only Tourmaline.

*168. Chrysolite, Olivine, Peridot.—($Mg$, Fe)$^2$ Si. Rhombic; $\alpha P$ ($a$) $130^\circ 2'$, $\beta P$ ($d$) $76^\circ 54'$, $\gamma P$ ($b$) $80^\circ 53'$; also $\alpha P$ ($M$), $\alpha P$ with $P$ ($p$), OP (fig. 152). The crystals are frequently prismatic and imbedded; also massive and granular. Cleavage, $\alpha P$ rather distinct; fracture conchoidal. $H = 6\frac{5}{6}...7\frac{5}{6}$; $G = 3...3\frac{3}{4}$. Transparent or translucent; vitreous. Olive-green, also yellow and brown, rarely colourless. B.B. infusible; soluble and gelatinizing in acids. Chem. com. 38 to 43 silica, 43 to 51 magnesia, 8 to 18 iron protoxide, with a little manganese. Chrysolite is the fine green transparent and crystallized varieties from the East, Esne in Egypt, and Brazil. Olivine, the darker and less pellucid, from Vesuvius, Unkel on the Rhine, the basalts of Germany, and the trap of Arthur Seat and other parts of Scotland; also in meteoric iron, as in the mass found by Pallas in Siberia, and in that of Otumpa in South America. Used as an ornamental stone, but not much valued.

The following seem mere varieties:

Hyalosiderite.—Brown or yellow, very ferruginous and metallic-looking; $H = 5$; $G = 2\frac{8}{9}$. In other respects like olivine; Kaiserstuhl in the Breisgau. Chusite, Limelite, and Tautolite; Lake Laach. Batrachite, greenish-gray or white, transluculent; Rizoni Mountain, Tyrol. Monelitite, transparent, colourless or yellowish; Vesuvius.

Fayalite.—Crystalline, columnar and foliated, but often as if fused. Greenish or pitch-black, brownish or brass-yellow, with a resinous metallic lustre. $H = 6\frac{5}{6}$; $G = 4\frac{1}{2}$. Partly soluble in h. acid. Chem. com. Fe$^2$ Si with 29-7 silica, 70-5 iron protoxide, and 2 to 8 manganese protoxide.

Knebelite.—Massive, opaque, gray, green, brown, or red. Chem. com. 32-5 silica, 32 iron protoxide, and 35 manganese protoxide.

Tephroite.—Granular, with two cleavages at right angles. $H = 5\frac{5}{6}$; $G = 4\frac{1}{2}$. Lustre adamantine. Ash-gray, with reddish-brown tarnish. Chem. com. 70 manganese protoxide and 30 silica. Franklin and Sparta, New Jersey.

169. Chondrodite, Macurite, $[nMg^2 \text{Si}^3 + [8 Mg F + Brucite, Humite.]$

Rhombic; $\alpha P$ $94^\circ 26'$, $\beta P$ $112^\circ 2'$; but crystals on three types, and often monoclinic in character or indistinct; chiefly in round grains or granular. Cleavage indistinct; fracture imperfect conchoidal. $H = 6\frac{5}{6}$; $G = 3\frac{15}{16}...3\frac{25}{32}$. Transparent or translucent; lustre vitreous or resinous. Yellow, red, brown, green, and almost black; streak white or yellowish. B.B. infusible, or only on very thin edges; decomposed by acids. Chem. com. 33 to 37 silica, 55 to 60 magnesia, 2-6 to 9-7 fluorine, with 1-7 to 6-7 iron protoxide. Chondrodite occurs at Pargas in Finnland, Åker, and Gullsjö in Sweden, Sparta in New Jersey, and Orange Family XIV.—Metallic Stones.

Crystallization predominantly rhombic; some tesselar or monoclinohedric; but many massive, or products of decomposition, and thus rather metallic clays or rocks. The crystalline species are rather hard; $H = 5\ldots6$; and with $G = 3\ldots6$. Those with high specific gravity are mostly infusible B.B., the others fusible. Most are soluble in acids, often gelatinizing. They are mostly silicates with a metallic base, and thus an intermediate group between the true stones and the metallic ores. Often opaque, and black or brown and yellow. They occur especially in the igneous and metamorphic rocks, or metallic veins of Scandinavia and the Ural.

170. Liévrinette, Yenite, Ilvaite.

Rhombic; $P$, polar edges $138^\circ26'$ and $117^\circ34'$, $\approx P 111^\circ12'$, $P \approx 112^\circ40'$. Crystals $\approx P2(s), P(o)$. Long prismatic and vertically striated; also radiated columnar or fibrous. Cleavages all imperfect; brittle. $H = 5\ldots6$; $G = 3\ldots4$. Opaque, resinous or imperfect metallic. Brownish or greenish-black; streak black. B.B. fuses easily to a black magnetic globule; soluble in h. acid forming a yellow jelly. Chem. com. 28% silica, 24% iron peroxide, 33% iron protoxide, and 13% lime. Rio in Elba, Fossum, Kupferberg, Rhode Island, and Greenland.

Wehrlite, iron-black, with greenish-gray streak, and B.B. difficulty fusible, is a variety; Hungary.

171. Hisingerite, Thrallite.

Reniform, or in crusts. $H = 3\ldots4$; $G = 2\ldots3$. Opaque; resinous. Brownish or bluish-black; streak liver or yellowish brown. B.B. fuses with difficulty; soluble in acids, leaving slimy silica. Chem. com. 32% silica, 33% iron peroxide, 15% iron protoxide, and 19 water, of the Thrallite from Bodenmais. Also Gillinge, Rydahyttan in Sweden, and Breitenbrunn in Saxony (Polyhydrite).

172. Antiosiderite.

Fine fibrous or flower-like; very tough. $H = 6\ldots5$; $G = 3$. Opaque or translucent; silky. Ochre-yellow to yellowish-brown. B.B. becomes reddish-brown, then black, and fuses with difficulty. Soluble in h. acid. Chem. com. 61% silica, 35% iron peroxide, and 4 water. Minas Geraes in Brazil.

173. Nontroite.

Massive. Fracture uneven. $G = 2\ldots2\frac{3}{4}$; $H = 2\ldots3$. Opaque; dull or glimmering; streak resinous. Straw-yellow, yellowish-white, or siskin-green. B.B. decrepitates, becomes black and magnetic, but without fusing; soluble, and gelatinizes in warm acids. Chem. com. nearly 43% silica, 36% iron peroxide, and 21 water, with 3% alumina and 2 magnesia. Nontroite in France, Harz, and Bavaria.

Chloropat is similar, but B.B. brown and infusible. Unghwari in Hungary, and near Passau. Pinguite, sectile; $H = 1$; feels greasy; and B.B. fuses on the edges; is also a silicate of iron oxides with water; Wolkenstein in Saxony, near Zwickau, and Suhl.

174. Chlorophyllite.

Massive. Cleavage in two directions; fracture conchoidal, earthy; very soft and sectile. $G = 2\ldots2\frac{1}{2}$. When first exposed translucent and pistacio or olive-green, but soon changes to brown or black, and opaque. B.B. melts to a black glass. Chem. com. of a specimen from Faroe, 32% silica, 22% iron protoxide, 3% magnesium, and 41% water. Scuir More in Rum, Faroe, and Iceland; also in Fife and near Newcastle.

175. Thorite.

Massive. Fracture conchoidal; hard and brittle. $G = 4\ldots6\frac{1}{2}$. Opaque; splendid; vitreous. Reddish-brown, or black clouded with red; streak dark-brown. B.B. infusible; gelatinizes with h. acid. Chem. com. essentially 73% thorina, 16% silica, and 9% water, but combined with very many other substances: lime, iron, manganese, magnesia, uranium, lead, tin, potash, soda, and alumina. Near Brevig in Norway.

176. Eulytine.

Tesseral and tetrahedral; $2O_2$ and $2O_2$. The crystals (like fig. 9) very small, and often with curved faces. Cleavage very imperfect; fracture conchoidal. $H = 4\ldots5$; $G = 5\ldots6$. Transparent and translucent; adamantine. Clove-brown, yellowish-gray or white; streak white or gray. B.B. fuses readily with intumescence to a brown bead, leaving a yellow ring on the charcoal; decomposed by h. acid, forming gelatinous silica. Chem. com. 21% silica and 79% bismuth peroxide, with 3% phosphoric acid, 2% iron peroxide, and 1% fluorine. Schneeberg, and Braunsdorf near Freiberg.

Hypochlorite or Green Iron-earth, also from Schneeberg, in reniform crusts, or very fine earthy; semitranslucent or opaque. Dull, and siskin or olive-green. $H = 6$; $G = 2\ldots3$. B.B. infusible, but becomes blackish-brown; and forms a yellow ring on the charcoal; insoluble in acids. It seems a mixture of silicate of iron and bismuth with phosphate of alumina.

177. Gadolinite.

Monoclinohedric, probably; with $Pco 49^\circ$, $\approx P 115^\circ$, $(2P \approx) 702^\circ$ nearly (Scheerer); but crystals rare and indistinct. Cleavage very indistinct, or none; fracture conchoidal or splintery. $H = 6\ldots5$; $G = 4\ldots4\frac{1}{2}$. Opaque or translucent on the edges; vitreous, often resinous. Black; streak greenish-gray. B.B. the conchoidal (vitreous) varieties incandescently, intumesce, but do not fuse; the splintery varieties form cauliflower-like ramifications, but do not incandesce; gelatinizes in h. acid. Chem. com. uncertain, but 25 to 29% silica, 30 to 51% yttria, 10 to 15 protoxide of iron, 5 to 17 protoxide of cerium with lanthanum, and 0 to 12 glucina. Krageroe in Norway, Ytterby, and Finbo.

178. Allanite, Cerin, Orthite.

Monoclinohedric, like epidote, but distinct crystals rare (fig. 154), mostly long, columnar, or granular. Cleavage imperfect; fracture conchoidal or uneven. $H = 6$; $G = 3\ldots3\frac{1}{2}$. Opaque, or translucent in thin splinters; imperfect metallic, inclining to vitreous or resinous. Black inclining to green or brown; streak greenish or brownish-gray. B.B. frothes, and melts easily to a black or brown scoria or glass, often magnetic; gelatinizes with h. acid. Chem. com. very variable, but with 30 to 35% silica, 12 to 18 alumina and iron peroxide, whilst R includes protoxides of cerium (11 to 24), lanthanum (2 to 8), iron (4 to 21), and manganese (0 to 3%). With lime (2 to 12), yttria (0.3 to 4), and magnesia (0.4 to 5). Allanite occurs in Greenland, also at Hitteroe, the Jotun Fjeld, and Snarum; Cerin at Rydderhyttan; Orthite at Finbo, Falun, Arendal, and Krageroe.

Pyrorhite, with carbonaceous and other matter; Uralorthite, from the Ilmen Mountains, containing more alumina; Bodenite, from Boden, Saxony; and Lagrationite, from Achmatowsk, are only varieties.

179. Tschegginite.

Massive. Fracture flat conchoidal. $H = 5\ldots5\frac{1}{2}$; $G =$ 45. Opaque; vitreous, splendid. Velvet-black; streak dark-brown. B.B. intumesces greatly, becomes porous, and often incandesces; in the strongest white heat fuses to black glass; gelatinizes with warm h. acid. Chem. com. 21 silica, 20 titanic acid, 11 iron protoxide, and 47 peroxides of cerium, lanthanum, and didymium. Ilmen Mountains near Miask.

180. Charno.—(Ce, R)²(Ce, R)²Si+H₂O.

Hexagonal; OP₁, OP₂, in low six-sided prisms, but very rare. Generally fine granular, almost compact. Cleavage traces; fracture uneven, splintery; brittle. H. = 5-5; G. = 4-9...5. Translucent on the edges, or opaque; dull, adamantine, or resinous; Clove-brown, cherry-red, or pearl-gray; streak white. B.B. infusible, but becomes dirty yellow; soluble in h. acid, leaving gelatinous silica. Chem. com. 22 silica, 72 protoxide of cerium (with didymium and lanthanum), and 6 water, with iron protoxide and lime. Bastnasite near Ridderhyttan.

181. Tetratomite.—Si₄, Ce, La, Ca, H₂O.

Tesseral in tetrahedrons. Fracture conchoidal; brittle. H. = 5-5; G. = 3-8...4-3. Vitreous; translucent on the edges. Dark-brown. B.B. swells and cracks; soluble in acids. Lamoe near Brevig.

182. Pyrochlore.—2(Ca, Th, Ce, Fe)Ni+NaF.

Tesseral; O. Cleavage octahedral; brittle; fracture conchoidal. H. = 5; G. = 3-8...4-3. Opaque or translucent; resinous. Dark reddish-brown, or almost black, some crystals ruby-red and transparent; streak pale-brown. B.B. becomes yellow and fuses with much difficulty into a blackish-brown scoria; the fine powder soluble in con. s. acid. Chem. com. very complex, but the Miaski variety, 62 to 67 niobic (mixed with titanic and tungstic) acid, 10 to 13 lime, 6 to 13 oxide of cerium and thorium, and 7 fluoride of sodium; but yttria, iron, zirconia, lithia, and in that from Norway, also uranium, occur. Miask in Ural, Brevig and Fredriksværn in Norway; also Chesterfield in Massachusetts (Microlite).

Pyrrhotite, small orange-yellow octahedrons; H. = 6; is a niobate of zirconia, with iron and uranium. Mursinsk and Azores.

183. Orstedbite.

Tetragonal; P 84° 26', like zircon. H. = 5-5; G. = 3-629. Opaque or translucent on the edges; adamantine vitreous. Reddish-brown. B.B. infusible. Forchhammer found 19-71 silica, 2-61 lime, 2-05 magnesia, 1-14 iron protoxide, 68-96 titanate of zirconia, 5-53 water. Arendal.

184. Keilhaute.

Yttriotitanite.

Monoclinohedric; C. = 58°, OP₁ = 114°. Cleavages, along -P intersecting at 138°. H. = 6...7; G. = 3-5...3-7. Translucent; vitreous or resinous. Blackish-brown; by transmitted light reddish; streak grayish-brown. B.B. fuses easily with effervescence to a black shining slag; with borax forms a blood-red glass in the red flame; in powder soluble in h. acid. Chem. com. 28-8 silica, 27-8 titanic acid, 19-5 lime, 9-3 yttria, 6-9 alumina, and 7-7 iron peroxide. Near Arendal.

185. Wöhlerite.

Rhombic; OP₁ = 127° 6', OP₂ = 140° 54'. Cleavage perfect; fracture conchoidal. H. = 5...6; G. = 3-41. Translucent; vitreous or resinous. Yellow, inclining to red or brown. B.B. fuses to a yellowish glass; easily soluble in warm con. h. acid, depositing silica and niobic acid. Analysis—30-62 silica, 14-47 niobic acid, 15-17 zirconia, 3-67 iron and manganese protoxide, 26-19 lime, and 7-78 soda. Fredriksværn (Eukolite), and Brevig in Norway.

ORDER II.—SALINE STONES.

Comprises minerals which, in external aspect and composition, resemble (or are) the salts of the chemist. With a few exceptions, as rock-salt and fluor-spar, they are combinations of the second order of two oxygen compounds. The acid component is one of the common acids,—the carbonic, sulphuric, boracic, or phosphoric acid,—not silica or alumina, as in the former order. They are almost all crystallized, and predominantly in rhombohedral or monoclinohedral forms, but some rhombohedral or tesseroid. Their hardness is low; one 7, a few about 5, most lower. G. = 1-5...4-7. All are soluble in acids, except the sulphates (three); more than half in water. B.B. all fusible or decompose. Many of them are products of decomposition. Occur rather in veins than as components of rocks.

**Family I.—Calc-spar.**

Generally rhombohedral in crystals and cleavage. H. = 3...4-5; G. = 2-6...3-4, becoming higher as the metallic element increases. They are soluble and often effervesce in acids; and become caustic or alkaline when burned. They form a series of closely-related compounds of carbonic acid with lime, magnesia, and isomorphous bases, as the protoxide of iron. Are generally white, translucent, with a vitreous, or pearly lustre.

**186. Calc-spar, Calcareous Spar, Carbonate of Lime.**

Rhombohedral; R 105° 5'; the forms and combinations exceeding those of any other mineral. Among them are more than thirty rhombohedrons, especially -R 135°, R₁ = 2R 79°, and 4R 66°, with OR and R as limiting forms; more than fifty distinct scalenohedrons, as R₁, R₂, and 4R₂; and the second hexagonal prism OP₂, whilst hexagonal pyramids are among the rarer forms. Some of the most usual combinations are OP₁ = ½R (fig. 157); or -½R₁ = OP₁, very frequent; also OP₁ OR₁; likewise -2R₁ R₁; R₁ = 2R₁ -2R₁; R₁ (g) = R₁ (r). R₁ (P₁) = 4R₁ (m). OP₁ (C) (fig. 155); and many others, upwards of an hundred distinct combinations being known.

Macles are not uncommon, especially with the systems of axes parallel (figs. 156, 157), and others conjoined by a face of R with the chief axes almost at right angles, 89° 5' (fig. 82); or by a face of -½R₁, in which the chief axes form an angle of 127° 5'; and usually many times repeated, so that the centre crystals appear in lamellae not thicker than paper (fig. 81). Cleavage, rhombohedral along R very perfect and easily obtained, so that the conchoidal fracture is rarely observable; brittle. H. = 3; G. = 2-6...2-8; pure transparent crystals = 2-72. Pellucid in all degrees. Very distinct double refraction. Lustre vitreous, but several faces resinous, and OR pearly. Most frequently colourless or white, but often gray, blue, green, yellow, red, brown, or black; streak grayish-white. B.B. infusible, but becomes caustic and emits a bright light; effervesces, and is entirely soluble in h. or n. acid. The fine powder ignited on platina-foil over the spirit-lamp, according to v. Zehmen, forms a somewhat connected mass, and even adheres to the platinum. Chem. com. of the purest varieties, carbonate of lime, with 48-57 carbonic acid and 56-13 lime, or 40 calcium, 12-2 carbon, and 47-8 oxygen; but usually contain magnesia and protoxide of iron or manganese. Remarkable specimens of the crystallized variety, or proper calc spar, are found in Andreasberg and other parts of the Harz (six-sided prisms), Freiberg, Tharandt, Maxen, Alston Moor in Cumberland (flat rhombic crystals), and in Derbyshire (pale yellow transparent pyramids).

Certain varieties are distinguished, as—Iceland spar, remarkable for its transparency and double refraction, occurs massive in a trap rock in that island. Slate spar, thin lamellar, often with a shining white pearly lustre, and greasy feel; Wicklow in Ireland, Glentilt in Scotland, and Norway. Aphrite, fine scaly, from Hessa and Thuringia. Marble is the massive crystalline variety of this mineral, produced by igneous action on compact limestone. Paros, Naxos, and Tenedos furnished the chief supply to the Greek artists; Carrara, near the Gulf of Genoa, to those of modern times. Some of the coloured marbles of the ancients were impure limestones, as the Cipollino, zoned with green tale or chlorite; and Verde antique, mixed with green serpentine. Ruin marble shows irregular markings like ruins; Val d'Arno (Florentine marble), and Bristol (Cotnam marble). Luculite, from Egypt, and Anthracite, from Kilkenny in Ireland, are black from carbon. Lumiachello, from Bleiberg in Carinthia, exhibits beautiful iridescent colours from fossil shells, sometimes deep-red or orange (Fire marble).

Limestone occurs in all formations under various names, as Oolite, egg or roe-stone, round concretions, with a concentric structure like the roe of fish; Pisolite, or peestone, similar structure; Chalk, soft earthy; Lithographic stone, yellowish and compact, from Solenhofen; and Marl, calcareous matter more or less mixed with clay. Tufa, or calcareous tufa, generally a recent deposit from calcareous springs, has often a loose friable texture, but at other times is hard and compact; and in the neighbourhood of Rome forms the common building stone or Travertino. The sandstone of Fontainbleau is carbonate of lime (±) mixed with quartz sand (§), and occasionally crystallizing in rhombohedrons.

This mineral is employed in many ways,—the coarser varieties, as lime, for mortar, manure, tanning, a flux in melting iron and other ores, or in preparing glass, and similar purposes; the finer, as marbles, for sculpture, architecture, and ornamental stone-work; the chalk for writing, whitewashing, or producing carbonic acid.

Plumbocalcite.—Cleavage, R.104°53'. White and pearly; softer than calc-spar; but G. = 2-824. Contains 2-3 to 7-8 carbonate of lead. Wanlockhead and Leadhills, Scotland.

**187. Dolomite, Bitter Spar.—CaCO₃ + MgCO₃.**

Rhombohedric; R 106°15'—20'; most frequent form R; also R and -½R, or OR, αR, and 4R. The rhombohedrons often curved and saddle-shaped; also granular or compact, often cellular and porous. Cleavage, rhombohedral along R. H. = 3-5...4-5; G. = 2-85...2-95. Translucent; vitreous, but often pearly or resinous. Colourless or white, but frequently pale-red, yellow, or green. B.B. infusible, but becomes caustic, and often shows traces of iron and manganese; fragments effervesce very slightly or not at all in hydrochloric acid; the powder is partially soluble, or wholly when heated; the very fine powder ignited on platinum-foil for a few minutes over a spirit-lamp continues pulverulent, but intumesces slightly during ignition. Chem. com. generally carbonate of lime, with more than 20 per cent. carbonate of magnesia and less than 20 per cent. carbonate of iron.

Varieties are—Dolomite, massive, granular, easily divisible, white; Rhomb or Bitter-spar, larger grained, or distinctly crystallized and cleavable, often inclining to green; and Brown-spar and Pearl-spar, in simple crystals or in imitative forms, of colours inclining to red or brown, more distinct pearly lustre, and under 10 per cent. carbonate of iron. Traversella in Piedmont, St Gotthardt, Gap in France, Alston in Cumberland, in Derbyshire, and at Leadhills and Charlestown in Scotland. Greenish, macleed; Mieno, in Tuscany (Miemite), and Tharandt in Saxony (Tharandite). Gurhofian, from Gurhof in Austria, is white and compact.

The massive and compact varieties are very common, and valued as building-stones (cathedral of Milan, York Minster, and the New Houses of Parliament). The Parian marble, and also the Iona marble in the Hebrides, have been supposed to belong to this species.

Predazzite.—Granular; white and vitreous on the cleavage planes. H. = 3-5; G. = 2-623. Contains 6-98 per cent. water. Predazzo in Tyrol.

188. Breunnerite, Giobertite.—MgCO₃. Rhombohedral; R 107°10'—30'; as yet only R; and granular or columnar. Cleavage, R very perfect, with straight faces. H. = 4...4-5; G. = 2-95...3-1. Transparent or translucent on the edges; highly vitreous. Colourless, but often yellowish, brown, or blackish-gray. B.B. infusible, but generally becoming gray, or black and magnetic; soluble in acids, often only when pulverized and warmed. Chem. com. essentially carbonate of magnesia, with 51-7 carbonic acid and 48-3 magnesia, but often mixed with 8 to 17 carbonate of iron or manganese. Tyrol, St Gotthardt, Harz, Fassatal; also Unst in Zeland.

Mesitine-spar, splendid, yellow, lenticular crystals; G. = 3-35...3-4; Traversella in Piedmont; and Pistomosite; G. = 4-4; Salzburg; are similar.

189. Magnesite.—MgCO₃. Reniform or massive. H. = 3...5; G. = 2-85...2-95. Sub-translucent or opaque; streak shining. Snow-white, grayish, or yellowish-white, and pale-yellow. Adheres slightly to the tongue. B.B. and with acids acts like breunnerite. Chem. com. pure carbonate of magnesia, with no metallic oxides. Tyrol, Norway, North America.

190. Hydromagnesite.—MgCO₃ + 4H₂O. Monoclinohedric; C = 82°16', P = 88° nearly. Crystals small, acicular; also massive. H. = 1-5...3-5; G. = 2-14...2-18. Vitreous or silky. White. B.B. infusible; soluble with effervescence in acids. Chem. com. 36-2 carbonic acid, 44 magnesia, and 19-3 water. Moravia, Kumi, Hoboken in New Jersey, and Texas in Pennsylvania. The Hydromagnacalcite is a similar yellow sinter from Vesuvius with part of the magnesia replaced by lime.

**191. Aragonite, Needle Spar, Flus-serril.—CaCO₃.**

Rhombic; P 116°16', P = 108°27'. The most common combinations are P = (h), P = (M), P = (k, P), generally long prismatic (like fig. 158, and separate crystals in fig. 159); P = P = P = 0P, generally short prismatic; 6P = P = P, acute pyramidal. But simple crystals are rare, from the great tendency to form macles, conjoined by a face of αP, and repeated (figs. 159, 160). Also columnar, fibrous, and in crusts, stalactites, and other forms. Cleav- age, brachydiagonal distinct, also $\infty P$ and $\overline{P}$ imperfect; fracture conchoideal or uneven. $H = 3\frac{1}{2}...4$; $G = 2\frac{3}{8}...3$ (massive 2-7). Transparent or translucent; vitreous. Colourless, but yellowish-white to wine-yellow, reddish-white to brick-red; also light-green, violet-blue, or gray. In the closed tube, before reaching a red heat, it swells and falls down into a white coarse powder, evolving a little water. A portion of this powder heated in the forceps, B.B., colours the flame carmine-red when strontia is present; on charcoal it becomes caustic, and with fluxes acts like calc-spar. Chem. com. carbonate of lime, occasionally mixed with $(0\cdot1...4)$ carbonate of strontia. Valencia, Molina, and in Arragon; Leogang in Salzburg, and Antiparos. Flor-ferri, coralloid, in the iron mines of Styria. Satinspar, fine fibrous silky, at Dufton; stalactite in Buckinghamshire, Devonshire, coast of Galloway, and Leadhills; also deposited as tufa by the Carlsbad and other hot springs.

Arragonite is most readily distinguished from calc-spar by falling to pieces at a low temperature, and by its less distinct and prismatic cleavage.

Tarnowitzite contains 2 to 4 carbonate of lead. Tarnowitz in Silesia.

**Family II.—Fluor Spar.**

Crystallization tesseral, hexagonal, or rhombic. $H = 4...5$, in one 7; $G = 2\frac{9}{10}...4\frac{1}{2}$, but mostly about 3. All soluble in acids, and mostly fusible or altered by heat. Those containing fluorine, when warmed with concentrated sulphuric acid, evolve vapours that corrode glass; those with phosphoric acid, when moistened with sulphuric acid, colour B.B. the flame green.

**192. Fluor Spar.—Ca F.**

Tesseral; the most common form is the cube $\infty O \infty$, then the octahedron $O$, and the rhombic dodecahedron $\infty O$; but many other forms occur in combinations. Macles are common; also course granular, columnar, or compact and earthy. Cleavage, octahedral perfect; conchoideal fracture; brittle. $H = 4$; $G = 3\frac{1}{2}...3\frac{1}{2}$. Pellucid in all degrees; vitreous. Colourless, but generally very various, and beautiful shades of yellow, green, blue, and red; often two or more in one specimen. Many varieties phosphoresce when heated (Chlorophane, with a bright green light). B.B. decrepitates, often violently, phosphoresces and fuses in thin splinters to an opaque mass; slowly soluble in h. or nitric acids, readily in s. acid, with evolution of hydrofluoric acid. Chem. com. neutral fluoride of calcium, containing 48-14 fluorine, and 51-86 calcium (=72-45 lime).

Fluor-spar is a very common mineral, chiefly in veins, as with tin ores in Saxony, Bohemia, Cornwall; with silver at Freiberg, Marienberg, Kongsberg; with lead in Derbyshire (near Castletown), Cumberland (Alston Moor), Northumberland and Ireland. It is rare in Scotland, but in greenstone near Gourock, in granite near Ballater in Aberdeenshire, on the Avon in Banffshire, and in Sutherland. In Derbyshire it occurs in large crystalline masses either with concentric colours or of a rich translucent blue (Blue John); and is wrought into various ornamental articles. Fluor spar is also used for etching on glass, and as a flux in reducing metallic ores, especially iron and copper.

**193. Yttrrocite.**

Very similar to fluor spar. Granular, crystalline, or in crusts. Cleavage imperfect. $H = 4...5$; $G = 3\frac{1}{2}...3\frac{1}{2}$. Translucent or opaque; weak vitreous lustre. Violet-blue to gray or white. B.B. infusible on charcoal alone, and evolves fluorine when heated with s. acid. Chem. com. fluorides of calcium, cerium, and yttrium, in variable proportions. Finbo and Brodlobo near Fahlun, Massachusetts, and Amity in New York.

**194. Fluocerite.—Ce F + Ce$^3$ F$^2$.**

Hexagonal; $\infty P$, OP. $H = 4...5$; $G = 4\frac{1}{2}$. Opaque or translucent on the edges; lustre weak. Pale brick-red or yellowish; streak yellowish-white. In the closed tube gives out fluorine. B.B. infusible. Chem. com. 82-64 peroxide of cerium, 1-12 yttria, and 16-24 hydrofluoric acid, Berzelius. Finbo and Brodlobo.

**195. Fluocerine.—Ce$^3$ F$^2$ + Ce H.**

Massive, with traces of cleavage; fracture conchoideal. $H = 4\frac{1}{2}$. Opaque; vitreous or resinous. Yellow, inclining to red or brown; streak brownish-yellow. B.B. infusible. Analysis, 84-21 peroxide of cerium, 10-85 hydrofluoric acid, and 4-95 water. Finbo. A similar mineral from Bastnaes gave fluoride of cerium (and lanthanum) 50-15, peroxide of cerium 36-43, and water 13-4.

**196. Chiolite.—3 Na F + Al$^3$ F$^2$.**

Rhombic (or tetragonal?), but only indistinct crystalline or granular. Cleavage, basal perfect, two others less so, the three nearly at right angles; brittle. $H = 2\frac{5}{6}...3$; $G = 2\frac{9}{10}...3$. Translucent, and after immersion in water almost transparent; vitreous, but on OP rather pearly. Colourless and snow-white, but often grayish, yellowish, or reddish. B.B. fuses very easily (even in the flame of a candle) to a white enamel; in open tube shows traces of fluorine; partially soluble in h. acid; wholly so in s., with evolution of fluorine. Chem. com. 53-7 fluorine, 13-1 aluminium, and 33-2 sodium. Arksfjord in West Greenland, Miask in Ural. Used as an ore of aluminium.

**197. Chiolite.**

$\begin{cases} 3 \text{Na F} + 2 \text{Al}^3 \text{F}^2 = A \\ 2 \text{Na F} + \text{Al}^3 \text{F}^2 = B. \end{cases}$

Tetragonal, with middle edge 113° 25' (or rhombic with $\infty P$ 124° 22'); mostly granular. Cleavage, P rather perfect. $H = 4$. Resinous. White. Very easily fusible (more so than cryolite), colouring the flame deep yellow; evolves fluoric acid. Chem. com. twofold; one variety (A) with $G = 2\frac{8}{10}...2\frac{9}{10}$, containing 18-7 aluminium, 23-8 sodium, and 57-5 fluorine; the second (B), with $G = 3\frac{1}{2}...3\frac{1}{2}$, containing 16-4 aluminium, 27-8 sodium, and 55-8 fluorine. Miask in Siberia.

**Fluellite.**

Small, white, transparent, rhombic pyramids; polar edges 109° 6' and 82° 12', middle 144°. Consists essentially of fluorine and aluminium. Stenna-gwyn in Cornwall.

**Prosopite.**

Crystals like datolite. $H = 4\frac{1}{2}$. Vitreous. Colourless and transparent. Contains fluorine, aluminium, calcium, and water. Altenberg; Schackenwalde (?).

**198. Hoprite.**

Rhombic; $\infty P$, 82° 20'; P with polar edges 106° 36' and 140°. Cleavage, macrodiagonal perfect. $H = 2\frac{5}{6}...3$; $G = 2\frac{7}{10}...2\frac{8}{10}$. Vitreous or pearly. Grayish-white. B.B. melts to a clear globule, tinging the flame green; soluble in acids without effervescence. Chem. com. oxide of zinc and cadmium, with phosphoric (or boracic?) acid, and much water. Altenberg near Aix la Chapelle.

**199. Apatite.—3 Ca$^3$ P + Ca (Cl, F).**

Hexagonal, and pyramidal-hemihedral; $P$ 80° 26'; the most common forms are $\infty P$ ($M$), $\infty P$ ($e$), OP ($P$), P ($x$). The crystals (figs. 161, 162) are short prismatic or thick tabular, and often striated vertically. Also granular, fibrous, or compact. Cleavage, prismatic and basal both imper- Mineralogical Science.

205. Hydroboracite.—Ca$^3$B$^3$+Mg$^3$B$^3$+12H$_2$O. Radiating and foliated like gypsum. H.$=2$; G.$=1$-9...2. Translucent. White, but partly red. B.B. melts easily, tinging the flame green; easily soluble in warm acids. Chem. com. 13-62 lime, 10-57 magnesia, 49-58 boracic acid, and 26-33 water. Caucasus. A similar mineral with soda in place of magnesia is found in Peru.

*206. Datolite, Borate of Lime.—Ca$^3$B$^3$+Ca$^3$Si$^3$+H$_2$O. Monoclinohedric; C.$=88°$19', $xP(f)77°$30', $xP(2g)$116°9', $P(P)122°$, $-2P(x)(a)43°$56', ($xP(x)(s),2P(x)(o)$ (fig. 164); or rhombic with $b:f90°$, $b:a135°$; $b:c141°$9', and $f:g160°$39'; also coarse granular. Cleavage, orthodiagonal and $xP$ very imperfect; fracture uneven or conchoidal. H.$=5$...5-5; G.$=2$-9...3. Transparent or translucent; vitreous; on the fracture resinous. Colourless or white, inclining to gray, green, yellow, and red. In closed tube yields water. B.B. intumesces, and melts easily to a clear glass, colouring the flame green; the powder gelatinizes in h. acid. Chem. com. 38-3 silica, 21-5 boracic acid, 34-6 lime, and 5-6 water. Arendal, Utoe, Andreasberg, Seisser Alpe, Sonthofen (Humboldtite); Togliani in Modena; also Salisbury Crags, Corstorphine Hill, and Glen Farg, in Perthshire; Connecticut and New Jersey.

Botryolite.—Fine fibrous, botryoidal or reniform, snow-white or hair-brown; otherwise, and in chem. com., like baltholite, but with two atoms water. Arendal.

Family III.—Heavy Spar.

Crystallization rhombic specially. H.$=3$...4-5; G.$=3$-2...4-7; but mostly 3-6...4-5. Soluble in acids, except barytes. B.B. fusible or decompose. Those containing barya colour the flame yellowish-green; those with strontia carmine red, best seen when moistened with h. acid. The sulphates fused with soda and then moistened leave a black stain on silver.

**207. Barites, Heavy Spar.—BaS$^3$. Rhombic; $P(o)(p)101°$40', $P(x)(f)74°$35', $P(x)(d)$102°17'; and OP($e$), (figs. 165, 166, 167). The crystals tabular or columnar, often in druses or groups; also foliated, fibrous, granular, or compact. Cleavage, basal perfect, prismatic along $xP$ less perfect; brachydiagonal traces. H.$=3$...3-5; G.$=4$-3...4-7(4-8). Transparent to translucent; vitreous or resinous. Colourless and white, but generally reddish-white, or flesh-red, yellow, gray, bluish, greenish, or brown. B.B. decrepitates violently, and fuses very difficultly, or only on the edges, colouring the flame yellowish-green; not soluble in acids. Chem. com. 34-3 sulphuric acid, and 65-7 barya, but occasionally with 1 to 15 sulphate of strontia. Very common, chiefly in veins, either alone or accompanying ores. Crystals at Dufton, Bohemia, Felsohanya and Kremnitz in Hungary, Auvergne, and United States. Columnar at Freiberg. The radiated from near Bologna, or the Bolognese stone, phosphoresces in the dark. Massive or Couch from Derbyshire and Staffordshire; in Scotland, at Leadhills, Braid Hills near Edinburgh, the Pentlands and Cheviots, and Arran, where mined as a white pigment.

**Lime Barytes** from Freiberg, Sonthain, and Derbyshire, seems a mixture with sulphate of lime; crystals tabular, in rosettes and other groups. $G = 4.0...4.3$.

**Hepatite**—Dark-gray, from carbonaceous matter; Kongsberg. **Allomorphite**, scaly, white and pearly, at Unterwirbach near Rudolstadt, agrees essentially (98-05 sulphate of baryta, 1-90 sulphate of lime) with barytes.

208. **Dreelite**—CaS + BaS. Rhombohedric; $R = 93°$. Cleavage, R imperfect. $H = 3...4$; $G = 3.2...3.4$. Lustre dull; on cleavage pearly. White. B.B. fuses to a white vesicular glass; effervesces with h. acid, but only partially dissolves. Chem. com. 61.73 sulphate of baryta, 14.27 sulphate of lime, 8.05 carbonate of lime, 9.71 silica, 2.40 alumina, 1.52 lime, 2.31 water. Nuisièere near Beaufieu.

*209. Wittehite*—BaC. Rhombic; $\alpha P = 118° 30'$, $\beta P = 68°$. Crystals $\alpha P$, $\beta P$ (fig. 168); more common spherical, botryoidal, or reniform, with radiated columnar texture. Cleavage, $\alpha P$ distinct, $2\beta P$ and $\beta P$ imperfect; fracture uneven. $H = 3...3.5$; $G = 4.2...4.3$. Semitransparent or translucent; vitreous, or resinous on the fracture. Colourless, but generally yellowish or grayish. B.B. fuses easily to a transparent globule, opaque when cold; on charcoal boils, becomes caustic and sinks into the support; soluble with effervescence in nitric or h. acid. Chem. com. 22.3 carbonic acid and 77.7 baryta. Alston Moor in Northumberland, and Lancashire, where it is used for poisoning rats; also in Styria, Salzburg, Hungary, Sicily, Siberia, and Chili.

210. **Alstonite**—BaC + CaC. Rhombic; $\alpha P = 118° 50'$, $2\beta P = 111° 50'$; usual combination $P$, $2\beta P$, $\alpha P$, resembling a hexagonal pyramid. Cleavage, $\alpha P$ and $\beta P$ rather distinct. $H = 4...4.5$; $G = 3.65...3.76$. Translucent; weak resinous. Colourless or grayish-white. Chem. com. 66 carbonate of baryta and 34 carbonate of lime, thus identical with the baryto-calcite. Fallowfield near Hexham, and Alston Moor.

211. **Baryto-Calcite**—BaC + CaC. Monoclinohedric; $C = 69° 30'$; $\alpha P = 95° 15'$, $P = 106° 54'$, $\beta P = 119°$ (fig. 169); also columnar and granular. Cleavage, P perfect, $\beta P$ less perfect. $H = 4$; $G = 3.6...3.7$. Transparent or translucent; vitreous, inclining to resinous. Yellowish-white. B.B. infusible, but becomes opaque and caustic. Chem. com. like Alstonite, Alston Moor.

*212. Celestine*—SrS. Rhombic; forms like those of barytes and sulphate of lead; $\alpha P = 104° 8'$, $\beta P = 75° 58'$. Usual combinations $\beta P$, $\alpha P$, OP, this with $\frac{1}{2}P$, also OP, $\alpha P$ (fig. 170); also columnar, and foliated; or fibrous, fine granular or compact. Cleavage, basal perfect; prismatic along $\alpha P$ less perfect. $H = 3...3.5$; $G = 3.9...4$. Transparent or translucent; vitreous or resinous. Colourless, but usually bluish-white to indigo-blue, and rarely reddish or yellowish. B.B. decrepitates and fuses easily to a milk-white globule; colours the flame carmine-red. Distinguished from barytes by a splinter after ignition in the inner flame, being moistened with h. acid, and held in the blue border of the flame of a candle, colouring this of a lively purple-red. Scarcely affected by acids. Chem. com. 43.6 sulphuric acid, and 56.4 strontia. Sulphur mines of Girgenti and other parts of Sicily, Herrengrund in Hungary, Bex, Salzburg, Monte Viale near Verona, and Meudon and Montmartre near Paris; in England near Bristol, and Knaresborough; in Scotland at Inverness, Tantallan Castle, Calton Hill. Used for strontium preparations, and red-light in fire-works.

**Baryto-celestine**—Radiating columnar or foliated. Bluish-white; very brittle and friable. $H = 2.5$; $G = 3.92$. B.B. difficultly fusible. Chem. com. 2 SrS + BaS, with 36 strontia, and 23 baryta. Diamond Island in Lake Erie, Kingston in Upper Canada, and Binmenthal.

*213. Strontianite*—SrC. Rhombic; $\alpha P = 117° 19'$, $\beta P = 105° 12'$. Crystals (fig. 171) and macles like aragonite; also broad columnar and fibrous. Cleavage, prismatic along $\alpha P$ ($M$), and $2\beta P$ ($P$) (69° 16') imperfect. $H = 3.5$; $G = 3.6...3.8$. Translucent or transparent; vitreous or resinous on fracture. Colourless, but often light asparagus or apple-green, more rarely grayish or yellowish. B.B. fuses in a strong heat only on very thin edges; intumesces in cauliflower-like forms, shines brightly, and colours the flame red; easily soluble with effervescence in acids; the solution in hydrochloric acid, evaporated and then dissolved in alcohol, makes this burn with a carmine-red flame. Chem. com. 30 carbonic acid and 70 strontia, but often contains carbonate of lime (6 to 8). Leogang in Salzburg, Bräunsdorf in Saxony, Hamm in Westphalia, the Harz, at Schoharie and other parts of the United States (Emmonite); Strontian in Argyllshire, Leadhills, Yorkshire, and Giant's Causeway. It is used to produce red fire in pyrotechnic exhibitions.

**Stromnite** or **Barystronianite**—Yellowish-white, semitranslucent, faint pearly lustre. $H = 3.5$; $G = 3.7$. Contains 68.6% carbonate of strontia, 27.5% sulphate of baryta, and 2.6% carbonate of lime. Stromness in Orkney.

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**Family IV.—Gypsum.**

Crystallization rhombic or monoclinohedric. $H = 2...3$, or less, many yield to the nail. $G = 2.2...2.9$, or also low. All, except the sulphates, soluble in acids, some in water; also fusible in general. Mostly translucent and colourless, but often coloured by mixtures.

*214. Gypsum*—CaS + H₂O. Monoclinohedric; $C = 81° 26'$; the most common forms are $\alpha P = 111° 14'$, $\beta P = 138° 44'$, $P = 143° 28'$, and ($\alpha P$). Two common combinations are $\alpha P$ ($f$), ($\alpha P$) ($P$), $P$ ($t$) (fig. 172), and this with $P$. Lenticular crystals often occur; macles frequent (fig. 83 above); also granular, compact, fibrous, scaly, or pulverulent. Cleavage; clinodagonal very perfect, hemipyramidal along $P$ much less perfect; sectile, thin plates flexible. $H = 1.5...2$ (lowest on $P$); $G = 2.2...2.4$. Transparent or translucent; vitreous, on cleavage pearly or silky. Colourless and snow-white, but often red, gray, yellow, brown, and more rarely greenish or bluish. In the closed tube yields water. B.B. becomes opaque and white; exfoliates and fuses to a white enamel, which is alkaline; soluble in 400 to 500 parts of water, scarcely more so in acids. Chem. com. sulphate of lime with two atoms water, or 46.47 sulphuric acid, 32.65 lime, and 20.88 water.

Gypsum is a very common mineral, often in nests or reniform masses in clay or marl. Transparent crystals, or **Selenite**, occur in the salt mines of Bex in Switzerland, of the Tyrol, Salzburg, and Bohemia, in the sulphur mines. of Sicily, at Lockport in New York, in the clay of Shotover Hill near Oxford, at Challey near Bath, and many other localities. Fibrous gypsum at Ilfeld in the Harz, and Matlock in Derbyshire. Compact gypsum at Volterra in Tuscany (Alabaster), and in whole beds in many parts of Germany, France, Italy, and England, often with rock-salt.

The finer varieties, or Alabaster, are cut into various ornamental articles. Plaster of Paris, used for casts and other works of art, is formed by calcining gypsum at a temperature below 300° Fahr., and grinding it down to a fine powder, which forms a paste that soon hardens by absorbing the water driven off by the heat.

215. Anhydrite, Muracite, Karstenite.—Ca S.

Rhombic; \( \alpha P = 91^\circ 10' \); \( \beta P = 96^\circ 36' \). Crystals OP, \( \alpha P \approx \infty \); \( \beta P \approx \infty \); \( \gamma P \approx \infty \), but rare; chiefly granular, or almost compact or columnar. Macles rare. Cleavage, macrodiagonal and brachydiagonal both very perfect, basal perfect. \( H = 3 \ldots 3\frac{1}{2} \); \( G = 2\frac{1}{2} \ldots 3 \). Transparent or translucent; vitreous; on \( \alpha P \) pearly. Colourless or white, but often blue, red, or gray; streak grayish-white. In closed tube gives no water. B.B. fuses difficultly to a white enamel; with fluor spar fuses readily to a clear globule, which becomes opaque when cold, and, on continuation of the heat, intumesces and becomes infusible; very slightly soluble in water or acids. Chem. com. 58-75 sulphuric acid and 41-25 lime.

The crystalline, or Muracite, occurs in the salt mines of Bex, Hall in Tyrol, and Aussee in Styria; also Sulz on the Neckar, and Bleiberg. Compact at Ischel in Austria, Berchtesgaden, Eiselen, and the Harz. Granular, or Vulpinite, near Bergamo. The contorted, or Gehroestein, chiefly at Wieliczka and Bochnia.

216. Pyritohalite.—\( 2 \text{Ca} \cdot \text{S} + \text{Mg} \cdot \text{S} + \text{K} \cdot \text{S} + 2 \text{H} \).

Rhombic; \( \alpha P = 115^\circ \); mostly columnar or fibrous. Cleavage, \( \alpha P \) imperfect. \( H = 3\frac{1}{2} \); \( G = 2\frac{1}{2} \ldots 2\frac{1}{2} \). Translucent; pearly or resinous. Colourless, but generally pale red, seldom gray. Weak bitter, and slightly saline taste. Soluble in water, leaving gypsum. B.B. fuses on charcoal to an opaque reddish bead, becoming white when cold. Chem. com. sulphates of lime 45, of magnesia 20-5, of potassa 28, and water 5-5. Ischel, Aussee, and Berchtesgaden.

217. Glauberite, Bronchiartin.—\( \text{Na} \cdot \text{S} + \text{Ca} \cdot \text{S} \).

Monoclinohedric; \( C = 68^\circ 16' \); \( \alpha P = 83^\circ 20' \); \( \beta P = 116^\circ 20' \). Crystals OP. \( \alpha P \), with \( \beta P \) (fig. 173). Cleavage, basal perfect, along \( \alpha P \) traces. \( H = 2\frac{1}{2} \ldots 3 \); \( G = 2\frac{1}{2} \ldots 2\frac{1}{2} \). Translucent; vitreous to resinous. Colourless, but yellowish or grayish-white. Taste slightly saline and bitter. B.B. decrepitates violently, and melts to a clear glass; decomposed by water, which removes the sulphate of soda. Chem. com. 51 sulphate of soda, and 49 sulphate of lime. Villarubia in Spain, Vic, Berchtesgaden; near Brugg in Aargau, Aussee and Ischel in Austria, and Tarapaca in Peru.

218. Alunite, Alumstone.—\( 3 \text{Al} \cdot \text{S} + \text{K} \cdot \text{S} + 6 \text{H} \).

Rhombohedric; \( R = 89^\circ 10' \). Crystals, \( R \) or \( R \cdot OR \) (fig. 174); also fine granular, earthy, or compact. Cleavage, basal rather perfect. \( H = 3\frac{1}{2} \ldots 4 \); \( G = 2\frac{1}{2} \ldots 2\frac{1}{2} \). Translucent; vitreous, on \( \alpha P \) pearly. Colourless and white, but grayish, yellowish, or reddish. B.B. infusible alone. Becomes blue with cobalt solution; soluble in warm con. s. acid, not in h. acid. Chem. com. 37-95 alumina, 10-66 potash, 39-42 sulphuric acid, and 11-97 water. Beregszasz in Hungary, Tolfa in the Papal States; also in Tuscany, near Naples, Lipari Islands, Auvergne, Milo, and Argentiera.

219. Alunitite, Websterite.—\( \text{Al} \cdot \text{S} + 4\frac{1}{2} \text{H} \).

Reniform, and very fine scaly or fibrous. Fracture earthy; sectile or friable. \( H = 1 \); \( G = 1\frac{1}{2} \). Opaque; dull or glimmering. Snow-white or yellowish-white. In closed tube yields much water. B.B. emits sulphurous fumes, the remainder being infusible; easily soluble in h. acid. Chem. com. 29-8 alumina, 23-2 sulphuric acid, and 47 water. Newhaven in Sussex; Eperney, Auteuil, and Lunel Vieil in France; Halle and Mori in Prussia.

220. Pharmacolite.—\( \text{Ca}^3 \cdot \text{As} + 6 \text{H} \).

Monoclinohedric; \( C = 65^\circ 4' \); \( \alpha P = 117^\circ 24' \); \( \beta P = 139^\circ 17' \). Crystals prismatic; often acicular or capillary, or radiated fibrous crusts. Cleavage, clinodimensional very perfect; sectile and flexible. \( H = 2\frac{1}{2} \); \( G = 2\frac{1}{2} \ldots 2\frac{1}{2} \). Translucent; vitreous; pearly or silky. Colourless and white, but sometimes rose-red or green. Yields water in the closed tube. B.B. fuses to a white enamel; in the inner flame on charcoal gives arsenic fumes, and fuses to a semi-translucent grain, colouring the flame blue; easily soluble in acids. Chem. com. 51 arsenic acid, 25 lime, and 24 water. Andreasberg, Riechelsdorf, Biber, Joachimsthal in Bohemia, Markirchen, and Wittichen in the Schwarzwald. Picroporpharmacolite contains magnesia. Roselite, vitreous; rose-red. B.B. with borax forms a deep blue glass. Chem. com. arsenic acid, oxide of cobalt, lime, magnesia, and water. Schneeberg in Saxony.

221. Haidingerite.—\( \text{Ca}^3 \cdot \text{As} + 3 \text{H} \).

Rhombic; \( \alpha P = 100^\circ \). Cleavage very perfect; sectile, flexible. \( H = 2\frac{1}{2} \); \( G = 2\frac{1}{2} \ldots 2\frac{1}{2} \). Transparent or translucent. Colourless and white. Chem. com. 85-68 arseniate of lime and 14-32 water. Joachimsthal in Bohemia.

222. Berzelite.—\( \text{Ca}^3 \cdot \text{As} + \text{Mg}^2 \cdot \text{As} \).

Massive, with traces of cleavage. Brittle. \( H = 5\frac{1}{2} \); \( G = 2\frac{1}{2} \). Translucent on the edges; resinous. Honey-yellow or yellowish-white. B.B. infusible, but becomes gray; soluble in nitric acid. Contains also 2 to 4 manganese protoxide. Longbanhjytta in Sweden.

223. Struvite, Guanite.—\( (\text{NH}^4 \cdot \text{O}) \cdot \text{Mg}^2 \cdot \text{P} + 12 \text{H} \).

Rhombic and hemihedral; \( \alpha P = 63^\circ 7' \); \( \beta P = 95^\circ \). Cleavage, brachydiagonal perfect. \( H = 1\frac{1}{2} \ldots 2 \); \( G = 1\frac{1}{2} \ldots 1\frac{1}{2} \). Transparent or opaque; vitreous. Colourless, but yellow or brown. In the closed tube yields water and ammonia. B.B. fuses to a white enamel; soluble in h. acid, and very slightly in water. Chem. com. 29-9 phosphoric acid, 16-3 magnesia, 10-6 ammonia, and 44 water. Under St Nicolai church at Hamburg, and in guano from Africa.

Family V.—Rock-Salt.

Crystallization monoclinohedric and rhombic, some tesseral and hexagonal. \( H = 1\frac{1}{2} \), but most about 2; \( G = 1\frac{1}{2} \ldots 3 \), but generally 2. All soluble in water, and B.B. fusible or decompose. When pure, mostly white, translucent, and vitreous. They are chiefly products of decomposition, and occur especially in the rainless regions, or in lakes not communicating with the sea.

224. Rock-Salt.—Na Cl.

Tesseral; almost always cubes. Generally granular and fibrous. Cleavage, hexahedral very perfect; fracture conchoideal; rather brittle; yields slightly when scratched with the nail. \( H = 2 \); \( G = 2\frac{1}{2} \ldots 2\frac{1}{2} \). Transparent or translucent; vitreous. Colourless or white, but often red, yellow, gray, and rarely blue. Taste saline. In the closed tube decrepitates, and yields a little water. B.B. on charcoal fuses and partly evaporates, partly sinks into the support. With soda fuses to a clear mass, colouring the flame yellow. Very soluble in water. Chem. com. 60 chlorine and 40 sodium, but often with various impurities.

This important mineral is very widely disseminated, either in thick masses, with clay, anhydrite, and gypsum, or as an efflorescence, covering extensive tracts of country. The most celebrated European deposits occur at Wieliczka and other parts of Galicia, in Hungary, Siebenburg, Moldavia, Styria, Salzburg (Hallein), in Tyrol (Hall); also in Bavaria, Wurtemburg, Switzerland (Bex), and Spain, especially at Cardona. In England the chief deposits are in Cheshire, as at Northwich. As an efflorescence it is most abundant on the sandy plains in Brazil, at the foot of the Atlas Mountains in Africa, in Abyssinia, in Arabia, and in the Steppes round the Caspian Sea and Lake Urak. Also as a sublimation among the lavas of Vesuvius.

Sylvite, or chloride of potassium, found as a sublimation on Vesuvius, and in the rock-salt of Hallein and Berchtesgaden, agrees in most characters with rock salt \((G = 1.9 \ldots 2)\).

- **225. Alum.** \(R = S^+ + (Al, Fe)S^+ + 24H\).

Tesseral; \(O\) sometimes with \(P\) and \(Q\). Generally fibrous crusts, or as an efflorescence. Cleavage, octahedral imperfect; fracture conchohedral. \(H = 2 \ldots 2.5\); \(G = 1.73 \ldots 1.9\). Translucent. Colourless and white. Taste sweetish astringent. Easily soluble in water. B.B. generally evolves sulphurous fumes.

(a.) Potash-alum, with \(R = K\), and 32-52 sulphuric acid, 10-86 alumina, 9-96 potash, and 45-66 water. In the closed tube it fuses, intumesces, and yields much water. In the Silurian alum-slates of Sweden, Norway, and Scotland; the coal formation, Hurlet and Campsie, in Scotland; the lias near Whitby; in the brown-coals of Hessia and the Rhine; and in the volcanic formations of the Lipari Islands, Sicily, and the Azores.

(b.) Ammonia-alum, with \(R = NH_4O\), and about 4 percent ammonia and 48 water. In the closed tube it forms a sublimate of sulphate of ammonia. Tschermig in Bohemia.

(c.) Soda-alum, with \(R = Na\), and 7 soda and 48 water. Like potash-alum, but more easily soluble. Near Mendoza in South America, the Sofatara at Naples, and Milo.

(d.) Magnesia-alum. \(R = Mg\) with Mn. Translucent and silky, but soon changes in the air. South Africa, Iquique in Peru (Pickeringite).

(e.) Iron-alum (Feather-alum), with \(R = Fe\). Hurlet near Paisley, Morsfield in Rhenish Bavaria, Krisuvig in Iceland (Heversite).

- **226. Voltaite.** \(3(Fe, K, Na)S + (Fe, Al)S^+ + 12H\).

Tesseral. Black, brown, or green; greenish-grey streak. Otherwise like alum, but more difficultly soluble in water. Soliflora of Pozzuoli.

- **227. Alunogen.** Halotrichite, Hair Salt. \(AlS^+ + 18H\).

Capillary or acicular, in crusts or reniform masses. \(H = 1.5 \ldots 2\); \(G = 1.6 \ldots 1.7\). Silky. White, inclining to green or yellow. Tastes like alum. B.B. in closed tube intumesces, yields much water, and is fusible. Chem. com. 36-05 sulphuric acid, 15-40 alumina, 48-55 water. Volcanoes of South America, coal and brown coal strata of Germany, and on old walls.

- **228. Mirabilite.** Glauber-salt. \(NaS^+ + 10H\).

Monoclinohedric; \(C = 72^\circ 15'\); \(P = 86^\circ 31'\); \(P' = 93^\circ 12'\). Crystals predominantly \(OP\) and \(P'OP\) (fig. 175); but generally efflorescent crystals. Cleavage, orthodiagonal very perfect; fracture conchohedral. \(H = 1.5 \ldots 2\); \(G = 1.4 \ldots 1.5\). Pellucid and colourless; taste cool, saline, and bitter; decomposes readily in the atmosphere, and falls into powder. Gives no precipitate with carbonate of soda. Chem. com. 19-3 soda, 24-7 sulphuric acid, and 56 water. As an efflorescence in quarries and on old walls in many countries, on Vesuvius in lava. Used in medicine, and in preparing glass and soap.

N.B.—No. 228-237 form a sub-family of Metallic salts, or Vitriols.

- **229. Melanterite.** Green or Iron Vitriol, Copperas. \(FeS^+ + 7H\).

Monoclinohedric; \(C = 75^\circ 40'\); \(P = 82^\circ 21'\); \(P' = 101^\circ 35'\); \(P'' = 69^\circ 17'\); \(P'''' = 118^\circ 19'\). Chiefly stalactitic, reniform, or in crusts. Cleavage, basal very perfect; \(P\) less so. \(H = 2\); \(G = 1.8 \ldots 1.9\). Translucent, rarely transparent; vitreous. Leek or mountain-green, often with a yellow coating; streak white. Taste sweetish astringent. Very soluble. B.B. becomes brown, then black and magnetic. Chem. com. 260 protoxide of iron, 28-8 sulphuric acid, and 45-2 water. Bodenmais, Rammelsberg in the Harz, Fahlun, Schemnitz, Bilin, and Hurlet near Paisley. Used in dyeing, in manufacturing ink, Prussian blue, and sulphuric acid.

- **230. Botryogene.** \(FeS^+ + 3FeS^+ + 36H\).

Red vitriol.

Monoclinohedric; \(C = 62^\circ 26'\); \(P = 119^\circ 56'\). Crystals small and short prismatic. More common botryoidal and reniform. Cleavage, \(P\) rather distinct. \(H = 2 \ldots 2.5\); \(G = 2.2 \ldots 2.1\). Translucent; vitreous. Hyacinth-red, orange-yellow, and yellowish-brown; streak ochre-yellow. Taste slightly astringent. Partially soluble in water, leaving a yellow ochre. Chem. com. sulphates of the protoxide and peroxide of iron (48), with 31 water, and about 21 sulphates of magnesia and lime; the two latter considered mixtures by Berzelius. Fahlun in Sweden.

- **231. Copiapite.** \(FeS^+ + 18H\).

Six-sided plates, but crystal-system uncertain; also granular. Cleavage perfect. Translucent; pearly. Yellow. Chem. com. 30-7 iron peroxide, 38-3 sulphuric acid, and 31 water. Copiapo in Coquimbo in Chili. Also radiated fibrous masses; dirty greenish-yellow, incrusting the former. Contain 32 sulphuric acid, and 37 water; but both are probably mixtures. To these may be added—

Fibroferrite, also from Chili. Yellow Iron-ore, from the brown coal at Kolosovuk in Bohemia and Modum in Norway. Both are reniform, or compact and earthy. \(H = 2 \ldots 3\); \(G = 2.7 \ldots 2.9\). Colour ochre-yellow. Not soluble in water, with difficulty in hydrochloric acid.

Apateit, reniform earthy, yellow, from Auteuil near Paris, is similar; also Vitriol ochre from Fahlun. Mixt., from Rammelsberg in the Harz, contains sulphates of iron, copper, zinc, and other metals.

- **232. Coquimite.** \(FeS^+ + 9H\).

Hexagonal; \(P = 58^\circ\). Crystals \(OP\), with \(P\) and \(P'\); usually granular. Cleavage, \(P'\) imperfect. \(H = 2 \ldots 2.5\); \(G = 2 \ldots 2.1\). White, also brown, yellow, red, and blue. Taste astringent. Chem. com. 28-5 iron peroxide, 43-6 sulphuric acid, and 28-9 water. Copiapo in Chili, and Calama in Bolivia.

- **233. Tectizite.** \(FeS^+ + 5H\).

Rhombic; dimensions unknown. \(H = 1.5 \ldots 2\); \(G = 2\) nearly. Vitreous or resinous. Clove-brown. Saxony near Schwarzenberg, and at Bräunsdorf.

- **234. Cyanose.** Blue Vitriol. \(CuS^+ + 5H\).

Triclinohedric. Crystals very unsymmetric; \(P = P'''\) (\(n\)) to \(P'''\) (\(r\)), forms an angle of 79° 19'; \(P' = P'''\) (\(T\)) 127° 40'; to \(P'''\) (\(n\)) 120° 50', to \(P'''\) (\(r\)) 103° 27', and...

235. Goslarite, White Vitriol.—Zn S + 7 H. Rhombic; \( \alpha P = 90^\circ 42' \), isomorphous with epsomite; \( \alpha P \). \( \alpha P \) (fig. 178). Mostly granular, or stalactitic, reniform, and encrusting. Cleavage, basal diagonal perfect. \( H = 2-2.5 \); \( G = 2-2.5 \); \( P = 2-2.5 \). Pellucid; vitreous. White, inclining to gray, yellow, green, or red. Taste nauseous astringent. Chem. com. 28-2 zinc oxide, 27-9 sulphuric acid, and 43-9 water. Rammelsberg in the Harz, Fablun, Schenmidt, Holywell in Flintshire, in Cornwall, at Villefranche, and Guipuzcoa in Spain. Used in dyeing and medicine.

236. Bieberite, Cobalt Vitriol.—(Co, Mg) S + 7 H. Monoclinohedric; similar to melanterite; usually stalactitic, or an efflorescence. Pale rose-red. Taste astringent. Chem. com. 20 cobalt oxide, 4 magnesia, 29 sulphuric acid, and 47 water. Bieber near Hanau, and Leogang in Salzburg.

237. Johannite, Uran Vitriol. Monoclinohedric; \( C = 85^\circ 40' \); \( \alpha P = 69^\circ \). Crystals similar to trona (fig. 181), but very small. Cleavage, \( \alpha P \). \( H = 2-2.5 \); \( G = 3-19 \). Semitransparent; vitreous. Bright grass-green, with paler streak. Chem. com. a hydrous sulphate of the protoxide of uranium. Joachimsthal and Johann-Georgenstadt.

238. Natron.—Na C + 10 H. Monoclinohedric; \( C = 57^\circ 40' \). Crystals similar to trona (fig. 179); with \( \alpha P \) (M) 79° 41', \( P \) (P) 76° 28'. Cleavage, \( \alpha P \) distinct; \( \alpha P \) less so. \( H = 1-1.5 \); \( G = 1-4-1.5 \). Pellucid; vitreous. Colourless or grayish-white. B.B. melts easily, colouring the flame yellow. Chem. com. 2-18 soda, 15-4 carbonic acid, and 6-28 water; but mixed with chloride of sodium, and other salts. On lava, as on Vesuvius and Etna; as an efflorescence on the ground in Hungary, Egypt, Tartary, and in mineral springs and lakes. Used in the manufacture of soap, in dyeing, bleaching, and medicine.

239. Thermonatrite.—Na C + H. Rhombic; \( \alpha P = (d) 107^\circ 50' \), \( P \) (o) 82° 50'; with \( \alpha P \) (P), in rectangular tables (fig. 180). Cleavage, \( \alpha P \) perfect. \( H = 1-5 \); \( G = 1-5 \). Colourless. B.B. like natron, but does not melt. Chem. com. 50-1 soda, 35-4 carbonic acid, and 14-5 water. Natron lakes of Lagunilla in Colombia, of Lower Egypt, and of the steppes between the Ural and Altai.

240. Trona, Uraco.—Na C + 4 H. Monoclinohedric. Crystals \( \alpha P \) and \( \alpha P \) (103° 15'), (fig. 181). Cleavage, \( \alpha P \) perfect. \( H = 2-5 \); \( G = 2-1-2-2 \). Transparent to translucent; colourless. Does not decompose in the air. Taste alkaline. Chem. com. 37-93 soda, 40-24 carbonic acid, and 21-83 water. Fezzan and Barbary (Trona), Lagunilla in Colombia (Uraco).

241. Gatlussite.—Na C + Ca C + 5 H. Monoclinohedric; \( C = 75^\circ 27' \); \( \alpha P = 68^\circ 51' \); \( P = 110^\circ 30' \). Cleavage, \( \alpha P \) imperfect; fracture conchoidal. \( H = 2-5 \); \( G = 1-9 \). Transparent; vitreous; colourless. Slowly and partially soluble in water. B.B. fuses readily to an opaque bead. Chem. com. 34-5 carbonate of soda, 33-6 carbonate of lime, 30-4 water, with 1-5 clay. Lagunilla near Merida.

242. Borax, Tinkal.—Na B + 10 H. Monoclinohedric; \( C = 73^\circ 25' \); \( \alpha P = 87^\circ \); \( P = 122^\circ 34' \). Almost isomorphous with augite. Twin crystals frequent. Cleavage, \( \alpha P \) perfect; \( \alpha P \) less distinct; fracture conchoidal, rather brittle. \( H = 2-2.5 \); \( G = 1-7 \). Pellucid; resinous. Colourless, but yellowish, greenish, and grayish-white. Taste feebly alkaline and sweetish. B.B. intumesces greatly, becomes black, and melts to a transparent bead, colouring the flame yellow, or, with sulphuric acid, green; soluble in 12 parts of cold water. Chem. com. of the pure salt, 16-37 soda, 36-53 boric acid, and 47-10 water; but often contains many impurities. Shores of salt lakes in Tibet and Nepal, and in South America near Potosi. Borax is prepared from this mineral, and is used for blowpipe experiments, in preparing fine glass, in medicine, and for dyeing.

243. Sassoline.—B + 3 H. Triclinohedric; \( \alpha P = 75^\circ 30' \); usually fine scaly six-sided tables, or fibrous, and stalactitic. Macles frequent. Cleavage, basal very perfect; sectile and flexible. \( H = 1 \); \( G = 1-4-1-5 \). Translucent; pearly. Grayish or yellowish-white. Taste acidulous and slightly bitter. Feels greasy. Easily soluble in boiling, less so in cold water. Froths up and melts in the candle flame to a hard transparent glass, colouring the flame green. Chem. com. 56-3 boric acid, and 43-7 water. Vulcano in the Lipari Islands, hot springs of Sasso near Sienna, and lagoon of Tuscany.

244. Nitre, Salpetre.—K N. Rhombic; \( \alpha P \) (M) 119°, \( 2P \) (P) 71°, \( P \) 110°, \( \alpha P \) (h), (fig. 182); isomorphous with arragonite. Only occurs acicular, capillary, or pulverulent. Cleavage indistinct; fracture conchoidal. \( H = 2 \); \( G = 1-9 \). Semitransparent; vitreous, or silky. Colourless, white or gray. Taste saline and cooling. Deflagrates when placed on hot charcoal; and B.B. on platina wire melts very easily, colouring the flame violet. Chem. com. 46-6 potash, and 53-4 nitric acid, but always more or less mixed. In the limestone caves of many countries, Hungary, Spain, India. Used for producing nitric acid, in glass-making, medicine, and the manufacture of gunpowder.

245. Nitratite.—Na N. Rhombohedric; \( R = 106^\circ 30' \), isomorphous with dolomite. Cleavage rather perfect. \( H = 1-5 \); \( G = 2-1 \). Translucent or transparent, with very distinct double refraction; vitreous. Colourless, or grayish and yellowish-white. Taste saline and cooling. Deflagrates on hot charcoal. B.B. fuses on platina wire, colouring the flame yellow. Chem. com. 36-6 soda, and 63-4 nitric acid, but mixed with common salt and other substances. Tarapaca in Chili. Used in the arts as a substitute for nitre; but deliquesces in the air.

246. Nitrocalcite.—CaN + H₂O. Fibrous or pulverulent. White or gray. Translucent. Taste sharp and bitter. Readily soluble in water, and deliquesces in the air; melts slowly on burning charcoal, with slight detonation. Chem. com. 32-00 lime, 57-54 nitric acid, and 10-56 water. Limestone caves of Kentucky; on old walls and limestone rocks.

247. Nitromagnesite.—MgN + H₂O. In the same places and similar to nitrocalcite. Taste bitter. Chem. com. 24 magnesia, 65 nitric acid, and 11 water.

*248. Sal-ammoniac.—NH₄Cl. Tesseral; O, also ∞O∞, ∞O, and 3O3. In crusts, stalactites, and earthy or pulverulent. Cleavage, O imperfect; fracture conchoidal. H. = 1-5...2; G. = 1-5...1-6. Pellucid; vitreous. Colourless, but gray or yellow, rarely green, brown, or black. Taste saline and pungent. B.B. volatilizes without fusing; on copper wire colours the flame bluish-green. Chem. com. (32 per cent. ammonia, or) 33-9 ammonium, and 66-1 chlorine. Chiefly occurs as a sublimate on active volcanoes, Vesuvius, Etna, the Solfatara, Vulcano, and Iceland; also near ignited coal seams, Newcastle, and Scotland. Used in medicine, dyeing, and various metallurgic operations.

249. Mascagnine.—NH₄S + H₂O. Rhombic; ∞P 107° 40', P∞ 121° 16'; ∞P∞, ∞P∞, P∞ (fig. 183); but chiefly in crusts and stalactites. Cleavage rather perfect; sectile. H. = 2-2.5; G. = 1-7...1-8. Pellucid, vitreous. Colourless, white or yellowish. Taste pungent and bitter; easily soluble, and deliquesces. B.B. decrepitates, melts, and volatilizes. Chem. com. 25-9 ammonia, 60-5 sulphuric acid, and 13-6 water. Near volcanoes, as Etna, Vesuvius, the Solfatara, the Lipari Islands, in the lagoons near Sienna, and in ignited coal beds, as at Bradley in Staffordshire.

250. Arganite, Glasereite.—K₂S. Rhombic; acute pyramids with ∞P 120° 24', P∞ 67° 38', OP, and other forms. Mostly in crusts, or pulverulent. Cleavage, basal imperfect. H. = 2-3...3; G. = 2-7. Pellucid; vitreous or resinous. Colourless or white. Taste saline, bitter. B.B. decrepitates, fuses, and becomes hepatic. Chem. com. 5-4-04 potash and 45-96 sulphuric acid. Lavas of Vesuvius and other volcanoes.

251. Thenardite.—Na₂S. Rhombic; acute pyramids P, with ∞P and ∞P, in crusts and druses. Cleavage, basal rather perfect; fracture uneven. H. = 2-5; G. = 2-6...2-7. Pellucid, vitreous. White. Taste feebly saline. B.B. colours the flame deep yellow, and fuses. Chem. com. 43-82 soda, and 56-18 sulphuric acid. Salinas d'Espartinas near Aranjuez, and Tarapaca. Used for preparing soda.

252. Lowrite.—(Na₂S + Mg₂S) + 5 H₂O. Compact with traces of one cleavage. H. = 2-5...3; G. = 2-376. Vitreous. Yellowish-white to flesh-red. Taste slightly saline. Chem. com. 20-3 soda, 13-2 magnesia, 52 sulphuric acid, and 14-5 water. Ischel.

*253. Epsomite, Epsom salt.—MgSO₄ + 7 H₂O. Rhombic; P mostly hemihedral, ∞P 90° 38'; ∞P (M), ∞P∞ (o), P (I) (fig. 184). Granular, fibrous, or earthy. Cleavage, brachydagonal perfect. H. = 2-2...2-5; G. = 1-75. Pellucid; vitreous; and white. Taste saline, bitter. B.B. on charcoal fuses, incandesces, and shows alkaline reaction; with solution of cobalt becomes pale rose-red. Chem. com. 16-32 magnesia, 32-53 sulphuric acid, and 51-15 water. Efflorescence on various rocks, as at Hurlet near Paisley, Idria, Montmartre, and Freiberg; on the ground in Spain, and the Russian steppes; in mineral waters, as at Epsom in Surrey (Epsom salts), Saidehütz and Seidhütz in Bohemia. Used in medicine and in preparing magnesia.

*Astrakanite.—White, transparent, prismatic crystals among the salts in the salt lakes near the Wolga. Chem. com. 41-00 sulphate of soda, 35-18 sulphate of magnesia, 21-56 water. Russin, white, six-sided, and pointed crystals, from Seidhütz and Saidehütz in Bohemia, is similar, but seems a mixture.

Order III.—Saline Ores.

Resemble the saline stones both in external characters and chemical composition, forming almost a parallel series, with metallic oxides in place of the earthy bases. Lime or magnesia occasionally occur in more or less extent, and the acid element is one of the common acids of the chemist. Crystallization in the carbonates is often rhombohedral, in the others monoclinobedric or rhombic. Other systems only occur in rare cases.

Hardness is not high, mostly 3...4, in a few as high as 5, and as low as 2. Their specific gravity is high, from the metallic element in their composition; mostly from 3...4 in the salts of iron or copper, and from 5...7 or 8 in the salts of lead and some others. They are almost all soluble in acids, and the carbonates effervesce. B.B. mostly fusible, decomposed, or reduced, and with fluxes form coloured glasses characteristic of the different metals. They are mostly translucent, rarely transparent. Their lustre is often pearly or vitreous. Some are white, others are coloured, and these colours are now characteristic of the metal as the essential element.

*Family I.—The Sparry Iron Ores.

Crystallization and cleavage rhombohedral. H. = 3-5...5; G. = 3-3...4-5. They are all soluble in acids, and often effervesce. B.B. they are all infusible, but decomposed, and leave a magnetic residue, and show reactions of metals. The colours are white, but often with a brown, yellow, or red tinge, especially when weathered. They chiefly occur in veins.

*254. Siderite, Sparry Iron, Sphärosiderite, FeCO₃. Chalybite.

Rhombohedral; R 107°. Chiefly R, often curved, saddle-shaped, or lenticular, occasionally OR, -½R, OR, -2R, ∞P₂. Frequently fine or coarse granular, more rarely botryoidal or reniform (Sphärosiderite). Cleavage, rhombohedral along R perfect. H. = 3-5...4-5; G. = 3-7...3-9. Translucent in various degrees, becoming opaque when weathered; vitreous or pearly. Rarely white, generally yellowish-gray or yellowish-brown, changing to red or blackish-brown on exposure. B.B. infusible, but becomes black and magnetic; with borax and salt of phosphorus shows reaction for iron; with soda usually for manganese. In acids soluble with effervescence. Chem. com. carbonate of iron, with 62-6 protoxide of iron and 37-9 carbonic acid, but usually 0-5 to 10, or even 25, protoxide of manganese, 0-2 to 1-5 magnesia, and 0-1 to 2 lime. In beds or masses, in Styria, Carinthia, and Westphalia; in veins in Anhalt and the Harz; also in the Pyrenees, and the Basque provinces of Spain, as near Bilboa. The crystals at Joachimsthal, Freiberg, Klausthal, Beerastone in Devonshire, Alston Moor in Cumberland, and in many of the tin mines of Cornwall. Clay ironstone, gray, blue, brown, or black; G = 2-8...3-5; H = 3-5...4-5, is an impure variety. It occurs chiefly in slate-clay or marls, in layers or nodular masses, especially in the coal formation of Britain, Belgium, and Silesia. These contain 50 to 85 per cent. carbonate of iron, and yield 25 to 42 metal. The Lanarkshire black band contains 70 carbonate of iron, 23 carbonaceous matter, 7 of silica, alumina, and lime, and yields 33-7 iron. In 1855 Great Britain produced 3,217,000 tons iron, worth about twelve millions sterling. South Wales alone produced about 839,000 tons, and Scotland 828,000 tons, worth nearly three millions sterling.

Junkerite, from Brittany, is a mere variety of siderite. Oligon spar, varieties with more than 20 per cent. manganese protoxide.

Ankerite.—R 106° 12', but mostly massive and granular. G = 2-9...3-1; otherwise like siderite. Contains 51 carbonate of lime, 12 to 33 carbonate of magnesia, 12 to 36 carbonate of iron, and 0 to 3 carbonate of manganese protoxide. Styria. Used as an ore or flux.

255. Diallopite, Red Manganese—Mn C. Rhombohedric; R 106° 51', R and -1/2 R, sometimes OR and OP 2. Crystals often curved, lenticular, or saddle-shaped; also spherical, reniform, and columnar or granular. Cleavage, R perfect. H = 3-5...4-5; G = 3-3...3-6. Translucent; vitreous or pearly. Rose-red to flesh-red; streak white. B.B. usually decrepitates and becomes greenish-gray or black, but is infusible; the powder soluble with effervescence in warm h. acid. Chem. com. 62 manganese protoxide and 38 carbonic acid, but usually mixed with carbonates of lime 0 to 13, magnesia 0 to 7, or iron 0 to 15. Freiberg, Schemnitz, Kapnik, Nagyag, Elbingerode, and near Sargans. At the latter, also hydrated, and fibrous, silky (Wiserite); compact in Hessa and Glen-dree, Ireland.

256. Manganocalcite.—(Mn, Ca, Fe) C. Rhombic; in prisms like aragonite, and bears the same relation to diallopite that aragonite does to calc-spar. H = 4...5; G = 3-03. Red or reddish-white; vitreous. Schemnitz.

257. Lanthanite.—La C + 3 H. Rhombic; OP 94° nearly; small tabular crystals; usually granular or earthy. Cleavage basal. H = 2-5...3; G = 2-7. Dull or pearly. White or yellowish. B.B. becomes brownish-yellow; soluble in acids with effervescence. Chem. com. 21-1 carbonic acid, 52-9 lanthanum oxide, and 26 water. Bastnas in Sweden, Lehigh in Pennsylvania.

258. Parisite.—Ce C, Ca F, H. Hexagonal; P 164° 58'. Cleavage, basal very perfect. H = 4-5; G = 4-35. Vitreous; on the cleavage planes pearly. Brownish-yellow inclining to red. B.B. infusible and phosphoresces. Chem. com. 23-6 carbonic acid, 60 protoxide of cerium, with lanthanum and didymium, 3-17 lime, 11-51 fluoride of calcium, and 2-4 water. Emerald mines of the Musso Valley in New Granada.

259. Calamine, Smithsonite.—Zn C. Rhombohedric; R 107° 40'; R, 4 R, and R². The crystals generally small, obtuse-edged, and rounded. Usually reniform, stalactitic, and laminar or granular. Cleavage, R perfect but curved; fracture uneven conchoidal; brittle. H = 5-0; G = 4-1...4-2. Translucent or opaque; pearly or vitreous. Colourless, but often pale grayish-yellow, brown, or green. B.B. becomes white, and acts like zinc oxide; soluble in acids with effervescence; also in solution of potash. Chem. com. 64-6 zinc oxide, and 35-4 carbonic acid, but with protoxide of iron 2 to 3, and manganese 3 to 7, lime 1 to 2, or magnesia 0 to 3.

This mineral occurs in beds or veins in the crystalline and transition rocks, and also in the carboniferous and oolite formations. It is most common in limestone, and is often associated with calc-spar, quartz, blende, and ores of iron and lead. Chassy near Lyons, Altenberg near Aix-la-Chapelle, Brilon in Westphalia, Tarnowitz in Silesia, Hungary, Siberia; also Mendip in Somersetshire, Matlock in Derbyshire, Wanlockhead and Lead Hills in Scotland; compact at Alston Moor. Zinc is obtained chiefly from this mineral by distillation. In Silesia also cadmium.

Kupferite, varieties with 15 to 37 per cent. of iron protoxide. Zine-bloom, reniform, earthy, pale-yellow, and shining streak; seems a mere produce of decomposition. Bleiberg and Raibel in Carinthia.

Herrertite.—Rhombohedric, with curved cleavage planes. H = 4...5; G = 4-3. Translucent; pearly or vitreous; green. B.B. becomes gray, fumes, and stains the charcoal white. Consists, according to Del Rio, of carbonates of zinc oxide and nickel oxide. Mexico.

*260. Galmei, Electric Calamine.—Zn² Si + H. Rhombic, and hemimorphic; OP 2 (P) with polar edges 101° 44' and 132° 16'; OP (d) 104° 6', OP (o) 117° 8', OP (l) 129° 2'; common form OP (s), OP, PO (fig. 185). Also columnar, fibrous, granular, and earthy. Cleavage, prismatic along OP very perfect, along PO perfect. H = 5; G = 3-3...3-5. Transparent to translucent; vitreous and pearly. Colourless or white, but often light gray, also yellow, green, brown, and blue; becomes electric by heat. B.B. decrepitates slightly, but is infusible; readily soluble in acids, and gelatinizes. Chem. com. 25-7 silica, 66-8 zinc oxide, and 7-5 water. With calamine, as at Raibel and Bleiberg in Carinthia, Aix-la-Chapelle, Iserlohn, Tarnowitz, and Nertschinsk; also Mendip Hills, Matlock in Derbyshire, and Wanlockhead. Used as an ore of zinc, and in the manufacture of brass.

261. Willmite, Troostite.—Zn² Si. Rhombohedric; R 115°; OP 2 R; also granular and reniform. Cleavage, basal rather perfect, OP imperfect; brittle. H = 4-5; G = 4-1...4-2. Translucent or transparent; dull resinous. White, yellowish, or brown. B.B. in closed tube yields no water, otherwise like galmei. Chem. com. 72-47 zinc oxide and 27-53 silica, with 0 to 9 protoxide of manganese, 0 to 5 iron protoxide, and 0 to 3 magnesia. Aix-la-Chapelle, Liege, Raibel, and Sterling; and Franklin in New Jersey.

**Family II.—Iron Salts.**

Crystallization predominantly rhombic or monoclinohedric. H = 2...5; G = 2-2...4. They are all soluble in acids, and many easily. B.B. all fusible, and also often easily so. Their colours are often brown, or dark blue and dark green; the streak yellow or red. They are chiefly phosphates or arseniates of iron. The phosphates B.B. moistened with sulphuric acid, colour the flame bluish-green. The arseniates B.B. in the reducing flame, or with carbonate of soda, evolve odour of arsenic.

*262. Vivianite, Blue Iron. 6 (Fe³⁺P + 8H) + (Fe³⁺P + 8H).

Monoclinohedric; C = 71° 25', OP 111° 12', PO 119° 10', PO 54° 13'. Crystals (OPx), OPx, PO (fig. 186); also spherical or reniform, and fibrous or earthy. Cleavage, clinodimensional very perfect; thin laminae flexible. H = 2; G = 2-6...2-7. Translucent or transparent; vitreous or bright pearly on cleavage. Indigo-blue to blackish-green; streak bluish-white, but soon becomes blue on exposure. The white earthy variety also changes to blue in the air; the dry crushed powder is liver-brown. In the closed tube yields much water, intumesces, and becomes spotted with gray and red. B.B. on charcoal becomes red, and then fuses to a gray, shining, magnetic granule; easily soluble in h. or nitric acid; becomes black in warm solution of potash. Chem. com., the colourless vivianite is a hydrous phosphate of iron protoxide, with 42 iron protoxide, 29 phosphoric acid, and 29 water; but on exposure, when it acquires a blue colour, with 29-1 phosphoric acid, 33-0 iron protoxide, 12-2 iron peroxide, and 25-7 water. Transparent indigo-coloured crystals at St Agnes in Cornwall, and Allentown and Imleytown in New Jersey. Earthy in Cornwall, Styria, North America, Greenland, and New Zealand, and in peat mosses in Northern Germany, Sweden, Norway, and the Zetland Isles. As a recent formation under some old slaughter-houses at the foot of the Castle Rock in Edinburgh. It is sometimes used as a pigment. Mullicite and Anglartite are varieties.

263. Dufrenite, Green Iron Earth.—$P^2 + P + H$. Rhombic; $\alpha P$ about 12° spherical or reniform. Cleavage brachydiaclonal; very brittle. $H = 3...3.5; G = 3.3...3.4$. Translucent on the edges, or opaque; shining or dull. Dirty, leek, or blackish green; streak siskin-green. B.B. fuses readily to a porous, black, non-magnetic globule; soluble in h. acid. Chem. com. 63 iron peroxide, 28 phosphoric acid, and 9 water. Westerwald, Hirschberg, and Limoges in France.

264. Triplite.—$Mn^4 + Fe^4 + P$. Rhombic (?); only granular. Cleavage, in three directions at right angles; fracture conchoidal. $H = 5...5.5; G = 3.6...3.8$. Translucent or opaque; resinous. Colour brown; streak yellow. B.B. decrepitates and fuses easily to a bluish-black magnetic globule; easily soluble in warm h. acid, showing traces of fluorine. Chem. com. 30-3 phosphoric acid, 41-4 iron protoxide, 23-3 manganese protoxide, and 6 fluorine. Zwiesel in Bavaria.

265. Zwieselite, Eisenapatite.—$(Fe, Mn)^4 + Fe^4 + P$. Rhombic (?), but only massive. Cleavage, in three directions imperfect; fracture conchoidal. $H = 4...4.5; G = 3.95...4.4$. Translucent on the edges; resinous. Colour brown; streak yellow. B.B. decrepitates and fuses easily to a bluish-black magnetic globule; easily soluble in warm h. acid, showing traces of fluorine. Chem. com. 30-3 phosphoric acid, 41-4 iron protoxide, 23-3 manganese protoxide, and 6 fluorine. Zwiesel in Bavaria.

266. Triphyline.—$6(Fe^4 + Mn^4) + Li^4 + P$. Rhombic; $\alpha P$ 94°; chiefly granular. Cleavage, basal perfect, prismatic and diagonal imperfect. $H = 5; G = 3.6$. Translucent on the edges; resinous. Greenish-gray with blue spots. B.B. fuses very easily to a dark steel-gray magnetic bead; easily soluble in h. acid. Chem. com. 42-64 phosphoric acid, 49-16 iron protoxide, 4-75 manganese protoxide, and 3-45 lithia. Bodenmais in Bavaria. Tetraphyline or Perowskite, from Tammela in Finland, is similar.

267. Monazite, Mengite.—$(Ce, La, Th)^4 + P$. Monoclinohedric; $C = 77°; \alpha P = 94°; \beta = 35°$; crystals of OP. $\alpha P = (\alpha P \times P)$. $P = -P$, with OP; $P = 129°6' OP; -P = 139°25' (fig. 187); thick, tabular, or very short prismatic. Cleavage, basal imperfect. $H = 5...5.5; G = 4.9...5.25$. Translucent on the edges; dull resinous. Flesh-red, hyacinth-red, and reddish-brown. B.B. infusible; moistened with sulphuric acid, colours the flame green; soluble in h. acid. Chem. com. 28 phosphoric acid, 25 to 37 cerium protoxide, 23 to 27 lanthanum oxide (18 thoria), with 2 tin oxide, 1-5 lime, and some magnesia and manganese. Miask in Ural, and Norwich in Connecticut (Edwardsite).

Monazitoid; $G = 5.281$; brown; partially soluble in acids, and with 18 phosphoric acid; probably a variety.

268. Cryptolite.—$Ce^4 + P$. Acicular crystals, imbedded in apatite. $G = 4.6$. Transparent. Pale wine-yellow. Soluble as powder in conc. s. acid. Wöhler's analysis gave 73-70 cerium oxide (protoxide), 27-37 phosphoric acid, and 1-51 iron protoxide. Arendal.

269. Hureauxite.—$(Mn, Fe)^4 + P + 8H$. Monoclinohedric; $C = 68°; \alpha P = 62°30'; P = 88°$; fracture conchoidal. $H = 3...3.5; G = 2.27$. Translucent; resinous. Reddish-yellow or brown. B.B. fuses easily to a black metallic globule; soluble in acids. Chem. com. 38 phosphoric acid, 11-1 iron protoxide, 32-9 manganese protoxide, and 18 water. Hureaux near Limoges.

Beraunite.—Foliated and radiated. $H = 2; G = 2.87$. Vitreous or pearly. Hyacinth-red or reddish-brown; streak reddish ochre-yellow. B.B. in forceps melts and colours the flame bluish-green; soluble in h. acid. Seems a hydrous phosphate of iron. Beraun in Bohemia. Kakoxene, from Zbirow in Bohemia, is similar.

Heterosite.—$H = 5; G = 3.5$. Opaque, or translucent on the edges; vitreous or resinous. Colour dark-violet or lavender-blue to greenish-gray; streak violet-blue or crimson-red. Chem. com. 41-77 phosphoric acid, 34-89 iron protoxide, 17-57 manganese protoxide, and 4-40 water. Hureaux near Limoges.

270. Alluaudite.—$(Mn, Na)^4 + P + Fe^4 + P + H$. Rhombic, with cleavage in three directions at right angles. $H$ above 4; $G = 3.468$. Translucent on the edges; lustre dull. Clove-brown; streak yellowish-brown. B.B. on platinum wire fuses to a black magnetic globule; in h. acid forms a black solution. Chem. com. 41-25 phosphoric acid, 25-62 protoxide of iron, 23-08 manganese protoxide, 1-06 manganese protoxide, 5-47 soda, 2-65 water, and 0-60 silica. Chanteloube near Limoges.

271. Diadochite.—$Fe^4 + P + 4Fe^4 + S + 32H$. Reniform and stalactitic. Fracture conchoidal. $H = 3; G = 2.035$. Resinous; vitreous. Yellow or yellowish-brown; streak white. B.B. intumesces, and fuses on the edges to a black magnetic enamel. Chem. com. 36-7 iron protoxide, 14-8 phosphoric acid, 15-2 sulphuric acid, and 30-3 water. Grafenthal and Saalfeld in Thuringia.

272. Delvauxite.—$Fe^4 + P + 24H$. Massive and earthy. $H = 2.5; G = 1.85$. Reddish or blackish brown or yellow. B.B. decrepitates, and fuses to a gray magnetic bead. In h. acid forms a brown solution. Chem. com. 35-8 iron protoxide, 48-3 water, and 15-9 phosphoric acid. Viézé in Belgium.

Korphenoiderite, reniform, opaque, resinous, and straw-yellow, with a greasy feel, is related. $H = 4.5; G = 2.5$. B.B. becomes red and fuses to a black magnetic bead; consists of hydrous phosphate of iron with a little oxide of zinc. Labrador.

273. Pissoiphane.—$(H, Fe)^4 + S + 15H$. Stalactite; fracture conchoidal; very easily frangible. $H = 2; G = 1.9...2$. Transparent or translucent; vitreous. Olive-green to liver-brown; streak greenish-white to pale yellow. B.B. becomes black; easily soluble in h. acid. Chem. com. 7 to 35 alumina, 10 to 40 iron protoxide, 12 sulphuric acid, and 41 water. Saalfeld, and Reichenbach in Saxony.

274. Pitticite, Iron Sinter.—$Fe^4S + 24FeAs + 24H$. Reniform and stalactitic; brittle; fracture conchoidal. $H = 2...3; G = 2.3...2.5$. Translucent, or on the edges; resinous, inclining to vitreous. Yellowish, reddish, or blackish-brown, sometimes in spots or stripes; streak light-yellow, or white. B.B. on charcoal fuses easily, with effervescence and strong arsenical fumes, to a black magnetic globule; easily soluble in h. acid to a yellow fluid. Chem. com. 35 iron peroxide, 26 arsenic acid, 14 sulphuric acid, and 24 water. In many old mines, as Freiberg and Schneeberg.

275. SIMPLESITE.

Monoclinohedric, like gypsum; in very fine prismatic crystals or groups. Cleavage perfect. H. = 2.5; G. = 2.957. Transparent or translucent; vitreous; pearly on the cleavage. Pale indigo to celadine-green, with bluish-white streak. B.B. emits arsenic odours, becomes black and magnetic, but does not fuse. Chem. com. arseniate of iron protoxide with water, also a little sulphuric acid and protoxide of manganese. Lobenstein in Reuss.

276. SCORODITE, Neocetse.—Fe As + 4 H.

Rhombic; P, with polar edges 103° 5' and 114° 34'. Crystals P and P (r); also OP (h), or P (d) 120° 10', and 2 P (m) 48° (fig. 188); also columnar and fibrous. Cleavage imperfect; rather brittle. H. = 3.5...4; G. = 3.1...3.2. Translucent; vitreous. Leek-green to greenish-black, also indigo-blue, red and brown. In closed tube yields water and becomes yellow. B.B. on charcoal fuses easily, emitting arsenic vapours, to a gray magnetic slag; easily soluble in h. (not in nitric) acid, forming a brown solution. Chem. com. 49-8 arsenic acid, 34-6 iron peroxide, and 15-6 water. St Austle in Cornwall, Vaulry in France, Schlackenwald and Schönfeld in Bohemia, Antonio Pereira in Brazil, and near Marmato.

277. ARSENOSIDERITE.—Ca As + 3 Fe As + 11 H.

Spherical and fibrous; friable, and leaves a mark on paper. H. = 1...2; G. = 3.52...3.88. Opaque; metallic pearly. Ochre brown, becoming darker in the air; streak brownish-yellow. B.B. fuses easily, with reaction for iron and arsenic. Chem. com. 39 arsenic acid, 40-7 iron peroxide, 11-9 lime, and 8-4 water. Romanèche near Mâcon in France.

278. PHARMAKOSIDERITE.—Fe As + 4e As + 18 H.

Cubic Ore.

Tesseral and tetrahedral; usually P with O, or P, or O. Cleavage, tesseral very imperfect; rather brittle. H. = 2.5; G. = 2.9...3. Semitransparent to translucent; adamantine or resinous. Olive to emerald-green, honey-yellow, and brown; streak straw-yellow. Pyro-electric. In closed tube yields water, and becomes red. B.B. on charcoal fuses easily to a steel-gray magnetic slag; easily soluble in acids. Chem. com. 40-4 arsenic acid, 28-1 iron peroxide, 12-6 iron protoxide, and 18-9 water. Huel Gorland, Huel Unity, and Carharrek in Cornwall; Burdle Gill in Cumberland; also St Leonard in the Haute-Vienne, Lobenstein in Reuss, Schwarzenberg in Saxony, and North America.

Beudantite, said to be rhombohedral; R 92° 30'. H. above 4. Resinous; black greenish-gray streak; but probably a mixture of pharmakosiderite with sulphate of lead. Horhausen in Nassau.

FAMILY III.—COPPER SALTS.

Crystallization generally rhombic and monoclinohedric. Hardness generally from 2...3.5, but a few as low as 1...2, others 4...5. Gravity 2...4, but mostly 3...4. The colours are predominantly green, and rarely blue. They are all soluble in acids, and mostly easily so. Mostly fusible B.B. and on charcoal, when moistened with hydrochloric acid, the copper is known by colouring the flame blue. With soda they are reduced to metallic copper. They are, with a few exceptions, compounds of copper with one of the common acids, and some used as ores of this metal. They occur especially in veins.

279. DIOPSITE, Emerald Copper.—Cu Si + H.

Rhombohedric; R 126° 24'; P 2 (s).—2 R (r) 95° 54' (fig. 189). Cleavage, R perfect; brittle. H. = 5; G. = 3.2...3.3. Transparent or translucent; vitreous. Emerald-green, rarely verdigris or blackish green; streak green. B.B. in the outer flame becomes black, in the inner red, but is infusible; soluble, and gelatinizes in h. or s. acid, and also in ammonia. Chem. com. 38-7 silica, 50 copper protoxide, and 11-3 water. Altyn-tube in the Kirgis Steppe.

280. CHYTOCOLLA, Copper-green.—Cu Si + 2 H.

Botryoidal, reniform, or investing; brittle; fracture conchoïdal, and fine splintery. H. = 2...3; G. = 2.0...2.3. Translucent or semitransparent; weak resinous. Verdigris to emerald green or azure-blue; streak greenish-white. B.B. and with acids like diopside. Chem. com. 34-83 silice, 44-94 copper protoxide, and 20-23 water. Saxony, Bavaria, Ural, Cornwall, Hungary, the Tyrol, Spain, the Harz (Silicose malachite), Mexico, and Chili.

281. AZURITE, Blue Copper.—Cu C + H.

Monoclinohedric; C = 87° 39', OP (M) 99° 32', -P (K) 106° 14'. Crystals OP. P. P. P. —P, or h, M, s, k, in fig. 190; also radiated and earthy. Cleavage, (P) (P) 59° 14', rather perfect; fracture conchoïdal or splintery. H. = 3.5...4.2; G. = 3.7...3.8. Translucent or opaque; vitreous. Azure-blue, the earthy varieties (and streak) smalt-blue. B.B. on charcoal fuses and yields a grain of copper; soluble with effervescence in acids, and also in ammonia. Chem. com. 69-1 protoxide of copper, 25-7 carbonic acid, and 6-2 water. Crystals at Chessy near Lyons, Kolyvan and Nischnie-Tagilsk in Siberia, Moldawa in the Bannat; also Redruth in Cornwall, Alston Moor, and Wanlockhead; massive in Cornwall, Thuringia, the Harz, Hessia, and the Ural. Valued as an ore of copper.

282. MALACHITE.—Cu C + H.

Monoclinohedric; C = 61° 49', OP 103° 42'; crystals OP (M) P (s). OP (P'), in macles (fig. 191). In general acicular, scaly, or reniform, stalactitic, and radiated fibrous. Cleavage, basal and clinodiagonal very perfect. H. = 3.5...4; G. = 3.6...4. Transparent or translucent on the edges; adamantine, vitreous, silky or dull. Emerald and other shades of green; streak apple-green. B.B., and with acids, like azurite. Chem. com. 71-8 copper protoxide, 20 carbonic acid, and 8-2 water. Crystalline at Rheinbreitenbach on the Rhine, and Zellerfeld in the Harz; fibrous and compact at Chessy in France, Siberia, the Ural, Saalfeld in Thuringia, Moldawa in the Bannat, Sandlodge in Zetland, Cornwall, Wales, and Ireland, and in North America and Australia. It is a valuable ore of copper, and the finer varieties are prized for ornamental purposes.

Lime-Malachite.—Reniform, botryoidal, and radiated fibrous; brittle. H. = 2.5. Silky; verdigris-green. B.B. blackens and fuses to a black slag; soluble in h. acid, leaving gelatinous gypsum. Seems a hydrous carbonate of copper and lime, with sulphate of lime and some iron. Lauterberg in the Harz. Mysorine, compact, blackish-brown, and soft; G = 2-62, is a mixture of a carbonate of copper with iron peroxide. Mysore in the East Indies.

283. Aurichalcite—$2 \text{Cu} + 3 \text{ZnH}$

Acicular. H. = 2. Translucent, pearly, and verdigris-green. B.B. on charcoal in the inner flame forms a deposition of zinc oxide, and with fluxes gives reaction for copper; soluble with effervescence in h. acid. Chem. com. 29-2 copper protoxide, 44-7 zinc oxide, 16-2 carbonic acid, and 9-9 water. Loktefskoi in the Altai; Matlock in Derbyshire.

Burattite, azure-blue, and agrees with aurichalcite, but perhaps mixed with lime. Loktefskoi.

284. Chalcopyrite, $[\text{Cu}^3\text{As} + 2\text{H}]$, or Copper-mica.

Rhombohedral; R 69° 48'. Crystals, OR (o). R (fig. 192). Cleavage, basal very perfect; sectile. H. = 2; G. = 4-2; ...2-6. Translucent or transparent; vitreous inclining to adamantine; pearly on OR. Emerald to grass or verdigris green; streak light-green. B.B. decrepitates violently, emits arsenical vapours, and fuses to a gray metallic grain; easily soluble in acids and ammonia. Chem. com. 49-6 copper protoxide, 18 arsenic acid, and 32-4 water; or 51-6 copper protoxide, 25 arsenic acid, and 23-4 water; but also 2 alumina, and 1-5 phosphoric acid. Tingtang, Huel Gorland and Huel Unity Mines near Redruth; also Saida in Saxony, and Moldawa in the Banat.

285. Tinstone.—$[\text{Cu}^3\text{As} + 10\text{H}] + \text{Ca} \text{C}$

Rhombic; reniform, or radiating foliated. Cleavage, basal very perfect; sectile. Thin lamina flexible. H. = 1-5...2; G. = 3...3-1. Translucent; pearly or vitreous, Verdigris-green to azure-blue; streak paler. B.B. decrepitates violently and fuses to a steel-gray bead; soluble in acids, evolving carbonic acid. Chem. com. 43-88 copper oxide, 25-01 arsenic acid, 17-46 water, and 13-65 carbonate of lime, by analysis. The carbonate of lime is perhaps accidental. Falkenstein in Tyrol, in Hungary, Reichelsdorf, Saalfeld, Piombino in Italy, in Asturia and at Linares in Spain, and Matlock in Derbyshire.

286. Erinite.—$[\text{Cu}^3\text{As} + 2\text{H}]$

Reniform and foliated; conchoidal fracture. H. = 4-5...5; G. = 4...4-1. Translucent on the edges; dull resinous. Emerald or grass green; streak similar. Chem. com. 59-9 copper protoxide, 34-7 arsenic acid, and 5-4 water. Lime-rick in Ireland. Cornucellite, is similar, but dark-green, and 5 H. Cornwall.

287. Liroconite.—$[\text{Cu}^3\text{As} + \text{Al} \text{As} + 24\text{H}]$

Rhombic; $\alpha P$ 119° 20', $\beta P$ 72° 22' (fig. 193). Cleavage, $\beta P$ imperfect and $\alpha P$ more so. H. = 2...2-5; G. = 2-8...3-0. Translucent; vitreous, or resinous on fracture. Azure-blue to verdigris-green; streak paler. In the closed tube does not decrepitate, but becomes green; then ignites and brown. B.B. on charcoal emits arsenical vapours and fuses; soluble in acids and in ammonia. Chem. com. 36-6 copper protoxide, 11-9 alumina, 26-6 arsenic acid, and 24-9 water. Huel Unity and other mines near Redruth; also Herregund in Hungary and Ullersreuth in the Voigtsland.

288. Olivinite.—$[\text{Cu}^3(\text{AsP}) + \text{H}]$

Rhombic; $\alpha P$ (r) 92° 30', $\beta P$ (q) 110° 50'; $\alpha P$ $\infty$ (n) (fig. 194); also spherical and reniform, and columnar or fibrous. Cleavage, (r) and (l) very imperfect. H. = 3; G. = 4-1...4-4. Pellucid in all degrees; vitreous, resinous, or silky. Leek, olive, or blackish-green, also yellow and brown; streak olive-green or brown. B.B. in the forceps fuses easily to a dark-brown adamantine bead covered with radiating crystals; on charcoal, detonates, emits arsenical vapours, and is reduced; soluble in acids and ammonia. Chem. com. 56-5 copper protoxide, 39-5 arsenic acid, and 4 water, but also 1 to 6 phosphoric acid. Carrara, Tin Croft, Gwennap, and St Day in Cornwall; also Alston Moor, Thuringia, Tyrol, Siberia, Chili, and other places.

289. Eucroite.—$[\text{Cu}^3\text{As} + 7\text{H}]$

Rhombic; $\alpha P$ (M) 117° 20', $\beta P$ (n) 80° 52', with $\alpha P$ (l), and OP (P), (fig. 195). Cleavage $\alpha$ and $\beta$ imperfect; rather brittle. H. = 3-5...4; G. = 3-35...3-45. Transparent or translucent; vitreous. Emerald or leek-green; streak verdigris-green. B.B. in forceps fuses to a greenish-brown crystallized mass; on charcoal detonates; easily soluble in nitric acid. Chem. com. 47-1 copper protoxide, 34-2 arsenic acid, and 18-7 water. Libethen in Hungary.

290. Klinoclaste, Aphanese, Abichite.—$[\text{Cu}^3\text{As} + 3\text{H}]$

Monoclinohedric; C = 80° 30', $\alpha P$ 56°; also wedge-shaped and hemispherical. Cleavage, basal highly perfect. H. = 2-5...3; G. = 4-2...4-4. Translucent or opaque; vitreous; pearly on the cleavage. Dark verdigris-green inclining to sky-blue; streak bluish-green. B.B. becomes black, and is reduced; soluble in acids and ammonia. Chem. com. 62-6 copper protoxide, 30-3 arsenic acid, and 7-1 water. Cornwall and the Erzgebirge.

291. Phosphorochalcite, Lunnite.—$[\text{Cu}^3\text{P} + 3\text{H}]$

Monoclinohedric; crystals ($\alpha P$) (r) 38° 56', P (P) 117° 49', with OP (a) and $\alpha P$ $\infty$ (e) (fig. 196); usually small and indistinct, more common in spherical or reniform, and radiated, fibrous. Cleavage, (e) imperfect; fracture uneven and splintery. H. = 5; G. = 4-1...4-3. Translucent, or on the edges; adamantine or resinous. Blackish, emerald, or verdigris green. B.B. decrepitates, or blackens and fuses to a black globule; easily soluble in nitric acid or ammonia. Chem. com. 70-8 copper protoxide, 21-2 phosphoric acid, and 8 water. Rheinbreitbach, Nishne-Tagisk, and in Cornwall. Dihydrite, with about a fifth less water. Copperdiaspore and Prasin seem varieties.

292. Thrombolite.—$[\text{Cu}^3\text{P} + 6\text{H}]$

Porodine. Fracture conchoidal; brittle. H. = 3...4; G. = 3-38...3-40. Opaque; vitreous. Emerald, leek, or dark-green. B.B. colours the flame blue and then green; on charcoal fuses easily. Chem. com. 45-1 phosphoric acid, 37-8 copper protoxide, and 17-1 water. Retzbanya in Hungary.

293. Libethene.—$[\text{Cu}^3\text{P} + \text{H}]$

Rhombic; $\alpha P$ (u) 92° 20', $\beta P$ (q) 109° 52', and P. (fig. 197). Cleavage, brachydiagonal and macrodiagonal imperfect. H. = 4; G. = 3-6...3-8. Translucent on the edges; resinous. Leek, olive, or blackish-green; streak olive-green. B.B., and with acids, acts like the phospho- Mineralogy.

294. **Tagilite**—Cu$^3$P + 3H. Fungoid or botryoidal, and radiating fibrous or earthy. H.$=3$; G.$=3.5$. Emerald-green. Chem. com. 61.8 copper protoxide, 27.7 phosphoric acid, and 10.5 water. Nischne-Tagilsk.

295. **Enlite**—Cu$^3$P + 3H. Botryoidal or reniform, and radiating foliated, or compact. Cleavage in one direction perfect. H.$=1.5...2$; G.$=3.5...4.2$. Translucent on the edges; pearly on the cleavage. Verdigris-green; streak paler. B.B. breaks into small fragments thrown about violently. Chem. com. 66.8 copper protoxide, 24.1 phosphoric acid, and 9.1 water. Ehl on the Rhine, Nischne-Tagilsk, and Libethen.

296. **Atacamite**—Cu Cl + 3 Cu H. Rhombic; $P(M)$ 112° 20', $P(P)$ 105° 40', and $P(h)$ (fig. 198); also reniform and columnar or granular. Cleavage (h) perfect. H.$=3...3.5$; G.$=4...4.3$ (3.7, Breit.) Semitransparent or translucent on the edges; vitreous. Olive, grass, or emerald-green; streak apple-green. B.B. fuses, and leaves copper; easily soluble in acids. Chem. com. 55.85 copper protoxide, 14.86 copper, 16.61 chlorine, and 12.68 water; or 74.46 copper protoxide and 17.09 h. acid. Remolinos and Santa Rossa in Chili, Tarapaca in Bolivia, Schwarzenberg, and on lavas of Aetna and Vesuvius. Used as an ore of copper.

297. **Volkonskite**—(Cu Ca)$^3$V + H. Hexagonal; small tabular crystals OP, $P(P)$ single or in groups. H.$=3$; G.$=3.45...3.89$. Olive-green; streak almost yellow. B.B. on charcoal fuses easily, and forms a graphite-like slag, containing grains of copper; on platina wire, with salt of phosphorus, forms a green glass; soluble in nitric acids, and with water gives a brick-red precipitate. Chem. com. 37 to 38 vanadic acid, 39.4 to 46 copper oxide, 18.5 to 13 lime, 3.6 to 5 water. Syssersk, Nischne-Tagilsk, and Friedericksrode in Thuringia.

298. **Brochantite**—Cu S + 3 Cu H. Rhombic; $P(P)$ 104° 10', $P(P)$ 151° 52', and $P(h)$; also reniform. Cleavage, brachydioagonal very perfect. H.$=3.5...4$; G.$=3.75...3.9$. Transparent or translucent; vitreous. Emerald or blackish-green; streak bright-green. B.B. on charcoal fuses, leaving copper; easily soluble in acids. Chem. com. 70 copper protoxide, 18 sulphuric acid, and 12 water. Rezbanya, Katharinenburg, and Roughtonhill in Cumberland; also Krisuvig in Iceland (Krisuvigite), and in Siberia (Koniginite).

299. **Uranite, Uran-Mica**—(Ca + U)$^3$P + 8H. Tetragonal; $P$ 143° 2'. Crystals OP, with $P(P)$ or $P(h)$ (fig. 199). Cleavage, basal very perfect; sectile. H.$=1...2$; G.$=3...3.2$. Translucent; pearly on OP. Siskin-green to sulphur-yellow; streak yellow. B.B. on charcoal fuses to a black semicrystalline mass; with soda forms a yellow infusible slag; in n. acids form a yellow solution. Chem. com. 15.5 phosphoric acid, 62.6 uranium peroxide, 6.2 lime, and 15.7 water. Johann-Georgenstadt and Eibenstock in Saxony, Autun and Limoges in France, Chesterfield in Massachusetts, and Lake Onega in Russia.

300. **Chalcolite**—(Cu + U)$^3$P + 8H. Tetragonal, and like uranite, but brittle. H.$=2...2.5$; G.$=3.5...3.6$. Grass to emerald or verdigris green; streak apple-green. B.B. like uranite, but with soda yields a grain of copper. Chem. com. 15.2 phosphoric acid, 61.1 uranium peroxide, 8.4 copper protoxide, and 15.3 water. Johann-Georgenstadt, Eibenstock, Schneeberg, Bodenmais, near Baltimore in North America, and near Redruth and St Austle.

301. **Erythrine, Cobalt-Bloom**—Co$^3$As + 8H. Monoclinohedric; ($P(P)$), ($P(P)$), ($P(P)$), ($P(P)$) (like fig. 186), with M.$=T=55°$; also $P(P)$ (h) 130° 10', and P (h) 118° 23' (fig. 200). Cleavage, clinodioagonal ($P$) very perfect; sectile; thin laminae flexible. H.$=1.5...2.5$; G.$=2.9...3$. Translucent; vitreous; pearly on the cleavage. Crimson or peach-blossom red. B.B. on charcoal fuses with arsenic fumes to a gray globule; colours borax blue; easily soluble in acids. Chem. com. 24 water, 38.2 arsenic acid, and 37.8 cobalt protoxide; but often with 0 to 8 lime, or the protoxides of iron 1 to 4, and nickel 0 to 9. Schneeberg, Saalfeld, Allemont, Riechelsdorf, the Pyrenees, and Modum in Norway; also Cornwall, Alston in Cumberland, at Alva in Stirlingshire, and Tyndrum in Perthshire. Used in preparing blue colours.

Kolbite.—White or peach-blossom red incrustations of minute crystals like erythrine, with which it agrees, except that the cobalt is almost wholly replaced by zinc. Schneeberg.

Kobaltbechlag, or Earthy-encrusting Cobalt, reniform or spheroidal, is a mixture of erythrine with arsenious acid.

Lavendulan.—Thin reniform lavender-blue crusts; translucent; resinous or vitreous. H.$=2.5...3$; G.$=2.95...3.1$. B.B. fuses very easily, colouring the outer flame blue. Consists of arsenic acid, protoxides of cobalt, nickel and copper, and water. Annaberg.

302. **Nickeline, Nickel-Ochre**—Ni$^3$As + 8H. Monoclinohedric (7); capillary and massive; earthy, rather sectile. H.$=2...2.5$; G.$=3...3.1$. Dull or glistening. Apple-green or greenish-white; streak greenish-white and shining. B.B. on charcoal fuses with arsenical vapours; easily soluble in acids. Chem. com. 38.7 arsenic acid, 37.3 nickel protoxide, and 24 water, but with a little cobalt or iron. Andreasberg, Annaberg, Saalfeld, Riechelsdorf, Joachimsthal, and Leadhills. Used in preparing blue colours.

Family IV.—Lead-Salts.

Crystallization predominantly rhombic and monoclinohedric in the salts of lead, but several tetragonal and hexagonal. Hardness moderate, or from 2...4.5, or generally about calc-spar. All have a high specific gravity, or from 5.3...8,—this family including all minerals without metallic lustre and aspect, with G. above 5.5. They are all soluble in nitric acid, and form coloured solutions or precipitates. They are all easily fusible, and mostly readily reduced alone, or with soda, to lead. They are mostly compounds of lead, and the cerussite is an ore of this metal. The others are not abundant, but often show fine colours. Occur chiefly in veins and mines with other ores of lead.

Lead B.B. on charcoal forms a greenish or sulphur-yellow coating round the assay. Solutions in nitric acid give, with sulphuric acid, a white precipitate; reduced B.B., and with chromate of potassa, a yellow precipitate.

303. **CERUSITE**, Lead Spar.—Pb C.

Rhombic; isomorphous with arragonite and nitre; \( \propto P (M) 117° 14' \), \( \propto P 108° 13' \), \( \propto P (u) 69° 18' \); also OP, P (t), \( \propto P (s) \), \( \propto P (l) \), \( \propto P (e) \) (figs. 201, 202).




Macles are very common (fig. 203); also granular or earthy. Cleavage, \( \propto P \) and \( \propto P \) rather distinct; fracture conchoidal; brittle and easily frangible. H. = 3...3.5; G. = 6...6.6 (earthy 5.4). Transparent or translucent; adamantine or resinous. Colourless and often white, but also gray, yellow, brown, black, rarely green, blue, or red; streak white. B.B. decrepitates violently, but easily fused and reduced; soluble with effervescence in nitric acid. Chem. com. 83.6 protoxide of lead and 16.4 carbonic acid. Very common at Przibram, Mies, and Bleistadt, Tarnowitz, Johann-Georgenstadt, Zellerfeld, Klausthal, Beeraston in Devonshire, St Minver's in Cornwall, Alston Moor, Keswick, Leadhills and Wanlockhead, and many other places.

304. **ANGLESITE**.—Pb S.

Rhombic; \( \propto P 103° 43' \), \( \propto P 75° 35' \). The crystals (fig. 204) short prismatic, or pyramidal, or tabular. Cleavage, prismatic along \( \propto P \) and basal, neither very perfect; fracture conchoidal; very brittle. H. = 3; G. = 6.2...6.3. Transparent or translucent; adamantine or resinous. Colourless and white, but occasionally yellow, gray, brown, or blue; streak white. Decrepitates in candle; B.B. on charcoal fuses in the ox. flame to a milk-white bead; very difficultly soluble in acids, wholly in solution of potash. Chem. com. 73.7 lead protoxide and 26.3 sulphuric acid, in some with a little silver. Zellerfeld, Clausthal, Badenweiler, Siegen, Silesia, Linares, Southampton in Massachusetts, Parys Mine in Anglesea, St Ives in Cornwall, Derbyshire, Leadhills and Wanlockhead. Compact (Bleiglas), Alston Moor in Cumberland.

305. **LEADHILLITE**.—\( 3 \text{ Pb C} + \text{Pb S} \).

Rhombic; P middle edge 137°, \( \propto P 120° 20' \), \( \propto P 43° 12' \). Crystals, OP, \( \propto P \) (fig. 205), mostly tabular; also macles. Cleavage, basal very perfect; slightly brittle. H. = 2.5; G. = 6.2...6.4 (6.0). Transparent or translucent; resinous or adamantine-pearly on OP. Yellowish-white, inclining to gray, green, yellow, or brown. B.B. on charcoal intrusomes, and becomes yellow, but again white when cold, and easily reduced; soluble with effervescence in nitric acid, leaving sulphate of lead. Chem. com. 72.6 carbonate and 27.4 sulphate of lead. Leadhills; also Grenada in Spain, and the Greek island Serpho.

306. **SUSANNAITE**.—\( 3 \text{ Pb C} + \text{Pb S} \).

Rhombohedric; R 72° 30'. Cleavage, basal perfect. H. = 2.5; G. = 6.55. White, green, yellow, or brown. Otherwise like Leadhillite. Susanah Mine, Leadhills.

307. **LANARKITE**.—Pb S + Pb C.

Monoclinohedric; \( \propto P 85° 48' \), \( \propto P 120° 45' \). Cleavage, basal very perfect; sectile, thin laminae flexible. H. = 2...2.5; G. = 6.3...7. Transparent; resinous or adamantine; on OP pearly. Greenish or yellowish-white, inclining to gray; streak white. B.B. on charcoal fuses to a white globule containing some metallic lead; partially soluble in nitric acid with effervescence. Chem. com. 53.15 sulphate and 46.85 carbonate of lead. Leadhills in Scotland.

308. **CALCEDONITE**.—\( 3 \text{ Pb S} + 2 \text{ Pb C} + \text{Cu C} (?) \).

Rhombic; \( \propto P 95° \), \( \propto P 109° \). Crystals \( \propto P \), \( \propto P \), \( \propto P \) (fig. 206). Cleavage, \( \propto P \) brachydagonal and microdagonal all imperfect. H. = 2.5...3; G. = 6.4. Transparent or translucent; resinous. Verdigris to mountain green; streak greenish-white. B.B. on charcoal easily reduced; soluble in nitric acid, leaving sulphate of lead. The solution is greenish, and shows reaction for lead and copper. Chem. com. 55.8 sulphate of lead, 38.8 carbonate of lead, and 11.4 carbonate of copper. Leadhills, Roughton Gill in Cumberland, and Rezhanya.

309. **LINARITE**.—Pb S + Cu H.

Monoclinohedric; \( \propto P 61° 0' \), \( \propto P 77° 15' \), \( \propto P 74° 25' \). Crystals \( \propto P \), OP, with the above or other forms; macles united by \( \propto P \). Cleavage, orthodagonal very perfect, and \( \propto P \) less so; fracture conchoidal. H. = 2.5...3; G. = 5.2...5.45. Translucent; adamantine. Azure-blue; streak pale-blue. Chem. com. 75.7 sulphate of lead, 19.8 copper protoxide, and 4.5 water. Wanlockhead, Leadhills, Roughton Gill, and Linares.

310. **PHOSGENITE**, Corneous Lead, \( \{ \text{Pb Cl} + \text{Pb C} \} \).

Cerasine.

Tetragonal; \( \propto P 113° 48' \). Crystals of \( \propto P \), OP, \( \propto P \), with P or \( \propto P \). Cleavage, \( \propto P \) rather perfect; fracture conchoidal. H. = 2.5...3; G. = 6...6.2. Transparent or translucent; resinous adamantine. White, yellow, green, or gray. B.B. fuses easily to an opaque yellow globule, citron-yellow or white and crystalline on cooling; soluble with effervescence in nitric acid. Chem. com. 51 chloride and 49 carbonate of lead. Very rare near Matlock in Derbyshire, and Elgin in Scotland.

311. **MENDIPITE**, Berzelite.—Pb Cl + 2 Pb.

Rhombic; but chiefly massive. Cleavage, along \( \propto P \) 102° 36' highly perfect; fracture conchoidal or uneven. H. = 2.5...3; G. = 7.0...7.1. Translucent; adamantine-pearly on the cleavage. Yellowish-white to straw-yellow and pale-red; streak white. B.B. decrepitates, fuses easily, and becomes more yellow; easily soluble in nitric acid. Chem. com. 40 chloride and 60 protoxide of lead = 85.8 lead, and 9.8 chlorine. Churchill in the Mendip Hills, and Brilon in Westphalia.

312. **MATLOCKITE**.—Pb Cl + Pb.

Tetragonal; \( \propto P 136° 17' \). Crystals, OP, P, P, small, thin, tabular. Cleavage, basal indistinct; fracture uneven conchoidal. H. = 2.5; G. = 7.21 (Greg), 5.39 (Ram.). Transparent or translucent; adamantine. Yellowish or greenish. B.B. decrepitates and fuses to a grayish-yellow globule. Chem. com. 55.6 chloride of lead, and 44.4 lead oxide. Matlock, on Galena.

313. **COTUXNITE**, Cotunnis.—Pb Cl.

Rhombic; \( \propto P 118° 38' \), \( \propto P 126° 44' \). Small acicular crystals. Transparent; adamantine. White. Easily scratched with the knife. G. = 5.238. B.B. on charcoal fuses easily, colours the flame blue, volatilizes as a white vapour, forms a white ring, and leaves a very little metallic lead; soluble in a large amount of water. Chem. com. 74 lead and 26 chlorine. Crater of Vesuvius after the eruption of 1822.

*314. **PYROMORPHITE**.—\( 3 \text{ Pb}^{\frac{3}{2}} \text{P} + \text{Pb Cl} \).

Hexagonal; \( \propto P 80° 44' \). Crystals \( \propto P \), OP, with \( \propto P^2 \), P Mineralogy.

315. MIMETITE.—Pb³⁺ As⁺⁺ + Pb Cl⁻

Hexagonal; P 81° 48'. Crystals, op. OP. P. or P. OP. Cleavage, P rather distinct, OP very imperfect; fracture conchoidal or uneven. H. = 3½...4; G. = 6.9...7. Translucent; colourless, but usually honey or wax yellow, yellowish-green, or gray. B.B. on charcoal fusible, but less easily than pyromorphite, with strong arsenical vapours. Chem. com. 90% arsenate and 9% chloride of lead; but part of the arsenic occasionally replaced by phosphoric acid. Johann-Georgenstadt, Zinnwald, Badenweiler, St. Prix in France, Nertschinsk, and Zacatecas in Mexico; Huell Alfred and Huel Unity in Cornwall, Caldbeckfield in Cumberland, and Beeralston in Devonshire.

Kampylite.—Orange-yellow; G. = 6.8...6.9; Chem. com. like mimetite, but contains phosphate of lime and chromate of lead. Alston in Cumberland and Badenweiler.

Hedyphane.—Crystalline masses with an imperfect hexagonal cleavage. G. = 5.4...5.5. Translucent; resinous adamantine. White. Chem. com. like mimetite, but with 13 arsenate and 15% phosphate of lime. Langhanshytta in Sweden.

316. BLEINTERITE.—Pb, Sb, H₂O

Reniform, spheroidal; earthy, or encrusting. H. = 4; G. = 3.9...4.76. Opaque; dull resinous, or earthy. Gray, brown, red, or yellow; streak grayish or yellowish-white. B.B. on charcoal reduced with antimony fumes. Chem. com. mixture of protoxide of lead (40 to 62), antimony oxides (31 to 47), and water (6 to 12); some also contain arsenic acid. Nertschinsk in Siberia, Cornwall.

317. VANADINITE.—Pb³⁺ V⁺⁺ + Pb Cl⁻

Hexagonal; OP. H. = 3; G. = 6.6...7.2. Opaque; resinous. Yellow and brown; streak white. B.B. decrepitates violently, and on charcoal fuses to a globule, which emits sparks and is reduced, colouring the support yellow; in the forceps fuses, and retains its yellow colour when cold; in nitric acid forms a yellow solution. Chem. com. 89% vanadate, and 10% chloride of lead. Zimapan in Mexico, Beresof in the Ural, and Wanlockhead.

318. DUCHEINT.—Pb V⁺⁺

Botryoidal or thin lamellar. H. = 3½...4; G. = 5.81. Resinous; translucent on the edges. Red or reddish-yellow; streak yellow. B.B. fuses easily to a yellow bead, and on charcoal reduced to lead; easily soluble in nitric acid. Chem. com. 54% lead oxide, and 45% vanadic acid, but analyses gave 46 to 49 of the latter. Niederschlettenbach in Rhenish Bavaria.

Similar are—Aravoxene; botryoidal; red, with a brown tinge. Chem. com. vanadic acid, with 48% lead oxide, and 16% zinc oxide. Dahn on the Rhine.

Euynchite.—Yellowish-red; opaque. B.B. melts easily to a lead-gray globule. Chem. com. 56 lead oxide, 23 vanadic acid, and 21 deutoxide of vanadium.

Desclouizite.—Pb V⁺⁺. In small rhombic crystals. Cleavage wanting; brittle. Translucent. Olive-green to black; on fracture concentric yellow and brown zones. B.B. fuses partially reduced. Chem. com. 54% lead oxide, and 22% vanadic acid, but also oxides of manganese, zinc, iron, and copper. La Plata.

319. WULFENITE.—Pb MoO₄

Tetragonal; P 131° 35'; OP (a), ½ P (b), P, OP, and PX (fig. 208). Cleavage, P rather perfect, basal imperfect; fracture conchoidal to uneven; rather brittle. H. = 3; G. = 6.3...6.9. Pellucid; resinous or adamantine. Colourless, but generally yellowish-gray, wax, honey, or orange yellow. B.B. decrepitates violently; on charcoal fuses and sinks into the support, leaving lead; in con. h. acid forms a yellow solution. Chem. com. 61% protoxide of lead and 38% molybdic acid. Bleiberg and Windisch Kappel in Carinthia, Retzbanya, Badenweiler, and Zacatecas in Mexico.

320. SCHEELITE, STOLZIT.—Pb WO₄

Tetragonal and hemihedral; P 131° 25'. Crystals, 2P. P. OP, spindle-shaped. Cleavage, P imperfect. H. = 3; G. = 7.9...8.1. Semitransparent or translucent; resinous. Gray, brown, yellow, or green. B.B. fuses to a dark crystalline grain; soluble in nitric acid, with a yellow precipitate. Chem. com. 51% tungstic acid and 48% protoxide of lead. Zinnwald in Bohemia and Coquimbo.

321. PLOMEGOMME.—Pb³⁺ V⁺⁺ + 6 H₂O

Reniform or stalactitic. Fracture conchoidal and splintery. H. = 4...4.5; G. = 3...6.4. Translucent; vitreous, inclining to resinous. Yellowish or greenish white to reddish brown, often in stripes. B.B. on charcoal becomes opaque and white, intumesces, and partially fuses; soluble in nitric acid. Chem. com. 38 protoxide of lead, 35 alumina, 8 phosphoric acid, and 19 water; but with 2 chloride of lead, a little iron peroxide and lime. Poullaouen in Brittany, and at Nassiere near Beaujeu. It much resembles gum-arabic.

322. CROCOCHITE, KROKOIT.—Pb Cr

Monoclinohedric; C = 78° 15'; OP 93° 44' (M), P 118° 58' (t), (OP) 56° 10' (r), (OP) (g) (fig. 209). Cleavage, OP rather distinct; sectile. H. = 2½...3; G. = 5.9...6.1. Translucent; adamantine, Hyacinth or aurora red; streak orange-yellow. B.B. decrepitates, blackens, and fuses on charcoal, the lower part being reduced; with borax or salt of phosphorus in the ox. flame a green, in the red flame a gray glass; soluble in warm h. acid. Chem. com. 31% chromic acid, and 68% lead protoxide. Beresof, Murinsk, and Nischnie-Tagilsk in the Ural; Congonhas do Campo in Brazil, Rezbanya, Moldawa, and Tarnowitz. Used as a pigment, but not permanent.

323. MILANOCHROITE, PHENIKOCHROITE.—Pb³⁺ Cr³⁺

Rhombic; dimensions unknown. Cleavage imperfect. H. = 3...3.5; G. = 5.75. Translucent on the edges; resinous or adamantine. Cochinchin to hyacinth red; streak brick-red. B.B. on charcoal fuses easily to a dark crystalline mass; in the red flame yields lead; soluble in h. acid. Chem. com. 23% chromic acid, and 76% protoxide of lead. Beresof.

324. VAUQUELINITE.—Cu³⁺ Cr³⁺ + 2 Pb³⁺ Ce³⁺

Monoclinohedric; C = 67° 15'. Crystals OP. - P. - P, always macleed (fig. 210), the faces of OP forming an angle of 134° 30' also botryoidal or reniform. H. = 2-5...3; G. = 5-5...5-8. Semitranslucent or opaque; resinous. Blackish or dark olive-green; streak siskin-green. B.B. on charcoal intumesces, froths up, and fuses to a dark-gray metallic globule surrounded by small grains of lead; in nitric acid forms a dark-green solution with a yellow residue. Chem. com. 60-87 lead protoxide, 10-80 copper protoxide, 28-33 chromic acid. Beresof, Congonhas do Campão Brazil.

325. Bismuthite.

Disseminated or investing. Fracture conchoidal or uneven; very brittle. H. = 4...4-5; G. = 6-8...6-91. Opaque; weak vitreous. Gray, yellow, or green. B.B. decrepitates, fuses very readily, and is reduced with effervescence; in h. acid it forms a deep-yellow solution. Chem. com. essentially carbonate, with a little sulphate of bismuth. Ullersreuth near Hirschberg, Schneeberg, and Johann-Georgenstadt.

326. Keratite, Hornsilver.—AgCl.

Tesseral; chiefly ∞O∞; small or very small; also massive. Fracture conchoidal; malleable and yields to the nail. H. = 1...1-5; G. = 5-3...5-4, or 5-5. Translucent; adamantine resinous; gray, occasionally bluish or greenish. B.B. fuses very easily to a gray, brown, or black bead, which in the inner flame is reduced; slightly affected by acids, and slowly soluble in caustic ammonia. Chem. com. 75 silver and 25 chlorine, but with some (0 to 6) iron peroxide. Johann-Georgenstadt, Joachimsthal, Huelgöet, Kongsberg in Norway, Spain, and Cornwall; now chiefly from Mexico and Peru. At Andreasberg in the Harz, mixed with clay (Buttermilchberg).

Carbonate of Silver (Seltbite), ash-gray, massive, very soft, effervescing in nitric acid, and B.B. easily reduced, seems a mixture. Wolfach in Baden, and Real de Catorce in Mexico (Plata azul, a rich silver ore).

327. Calomel—Hg₂Cl₂.

Tetragonal; P 185° 50'. Crystals like fig. 118 above but very small; sectile. H. = 1...2; G. = 6-4...6-5 (artificial 7-0). Translucent; adamantine. Grayish or yellowish-white. In the closed tube it sublimes as a white mass, and with soda yields mercury. B.B. on charcoal, when pure, wholly volatilizes; in nitric acid not soluble, in h. acid partially. Chem. com. 15 chlorine and 85 mercury. Moschellandsberg in Rhenish Bavaria, also Idria and Almaden.

328. Iodite.—AgI.

Thin flexible plates. Malleable. H. = 1...1-5; G. = 5-5...5-7. Translucent; lustre inclining to adamantine. Pearl-gray, yellowish-gray, or greenish-yellow. B.B. on charcoal becomes red, fuses easily, colouring the flame purple-red, and leaves a grain of silver. Chem. com. 54 iodine and 46 silver. Albarradon in Zacatecas, Mexico; Arqueros in Chili, and Guadalajara in Spain.

329. Coccinite.—HgI₂.

Scarlet-red, easily fusible, and subliming; said to occur at Casas Viejas in Mexico, and to be used as a pigment. Chem. com. probably 44-3 mercury and 55-7 iodine, like the artificial salt, which crystallizes in tetragonal pyramids.

330. Bromite.—AgBr.

Tesseral; ∞O∞ and O. Crystals very small; also crystalline grains. H. = 1...2; G. = 5-8...6. Very splendid. Olive-green or yellow, with gray tarnish; streak siskin-green. B.B. very easily fusible; scarcely affected by acids. Chem. com. 57-5 silver and 42-5 bromine. San Onofre in the district of Plateros in Mexico (Plata verde), and used as an ore of silver.

331. Embolite—2 Ag Br + 3 AgCl.

Tesseral; ∞O∞ and O. H. = 1...1-5; G. = 5-3...5-4 or 5-8 (Breit). Resinous and adamantine. Yellow or green. Chem. com. 67 silver, 20 bromine, and 13 chlorine. Chili, Mexico, and Honduras. Ore of silver.

332. Romeite, Romeine.—Ca₃Sb₂Sb.

Tetragonal; P 110° 30'; consequently very like an octahedron. Scratches glass. G. = 4-6...4-7. Honey-yellow or hyacinth-red. B.B. fuses to a blackish slag; not soluble in acids. Chem. com. 41-3 antimonic acid, 37-3 antimony oxide, and 21-4 lime, but with 2 to 3 manganese and iron protoxide. St Marcel in Piedmont.

333. Scheelite, Tungsten.—CaW.

Tetragonal and hemihedral; P 112° 2'; often alone. The usual combinations are P (P), 2 P∞ (g), (fig. 211). Cleavage, 2P∞ 129° 2' rather perfect, along P and OP less perfect. Fracture conchoidal and uneven. H. = 4...4-5; G. = 5-9...6-2. Translucent; vitreous, inclining to resinous or adamantine. Colourless, but gray, yellow, or brown; streak white. B.B. fuses difficulty to a translucent glass; decomposed in h. or n. acid, leaving tungstic acid; also in solution of potash. Chem. com. 80-6 tungstic acid and 19-4 lime, but with 0 to 3 silica and 0 to 1-5 iron peroxide, or rarely copper protoxide when the mineral is green. Caldbeckfell near Keswick; Pengilly, Cornwall; at Zinnwald and Schlackenwald in Bohemia; also in the gold mines of Salzburg and of Hungary; Chili and Siberia; also in the Monroe Mines in Connecticut, where used in preparing tungstic acid, a very fine yellow pigment.

ORDER IV.—OXIDIZED ORES.

Crystallization rhombic, then tesseral or tetragonal, less frequently hexagonal or rhombohedral. Hardness generally high, or 5...7, most equal to felspar. Gravity also high, or 4...7 or 8. They are generally soluble in acids and solutions coloured. B.B. infusible, or very difficultly so. Chem. com. oxides of the metals alone or in composition. They are mostly opaque, with metallic lustre, and of black, brown, or dark-gray colours. Occur in beds, veins, or large masses, especially in the metamorphic and igneous rocks.

FAMILY I.—OXIDIZED IRON ORES.

Crystallization tesseral, rhombohedral, or rhombic. H. = 5...6-5; G. = 3-4...6-5; crystalline species 4-5...5-3. Soluble in acids; solution green. B.B. infusible or very difficult, but becomes magnetic in the red. flame. With borax show reaction for iron. Colours black, brown, or red. Occur in beds, veins, or large masses in the older rocks, or as rock constituents.

334. Magnetite, Magnetic Iron.—Fe₃O₄.

Tesseral; O and ∞O, also ∞O∞; 202 and 20. Macles common, united by O (fig. 212). Generally granular or almost compact; often also in loose grains. Cleavage, octahedral perfect, or mere traces; fracture conchoidal or uneven; brittle. H. = 5-5...6-5; G. = 4-9...5-2. Opaque; lustre metallic. Iron-black, or inclining to brown or gray; highly magnetic. B.B. becomes brown and non-magnetic, and fuses with extreme difficulty; powder soluble in h. acid. Chem. com. 31-03 of the protoxide, and 68-77 of the peroxide of iron, or 72.4 iron and 27.6 oxygen. Crystals at Traversella in Piedmont, Greiner in Tyrol, Kraun in Styria; large masses Arendal in Norway; Dannebrog, Utoe, Norberg, Taaberg in Sweden; Kurunavara and Gellivara in Lapland; Nischnie-Tagilsk, Blagodat, and the Kaschkanar in the Ural; also Scotland, the Harz, Saxony, Bohemia, Silesia, Elba, and Spain; Mexico, Brazil, and North America. Magnetite is the most important ore of iron in Norway, Sweden, and Russia.

*335. Chromite.—(Fe, Mg) (Cr, Al).

Tesseral, only in octahedrons; generally granular. Cleavage, octahedral imperfect; fracture imperfect, conchoideal, or uneven. H. = 5-5; G. = 4-4...4-5. Opaque; semi-metallic or resinous. Iron or brownish-black; streak yellowish or reddish-brown. Sometimes magnetic. B.B. infusible and unchanged, but the non-magnetic in the red flame become magnetic; in borax forms an emerald-green bead; scarcely affected by acids. Chem. com. 19 to 37 iron protoxide, 0 to 10 magnesia, 56 to 60 chrome peroxide, and 9 to 21 alumina, with 0 to 10 silica as a mixture. Saxony, Silesia, Bohemia, Styria (Kraubath), Gasslin in the Var dept. in France, Röraas in Norway, Katherinenburg in the Ural, near Baltimore, Chester in Massachusetts, and Hoboken; in Scotland in great abundance in Umst and Fetlar in the Zetlands, at Portsoy in Banff, and Tyndrum. Used in the preparation of various pigments.

336. Franklinite.—(Fe, Zn, Mn) (Fe, Mn) (?).

Tesseral; O and O. = O; also granular. Cleavage, octahedral, but very imperfect; fracture conchoideal or uneven; brittle. H. = 6...6-5; G. = 5-0...5-3. Opaque; imperfect metallic lustre. Iron-black; streak dark reddish-brown. B.B. infusible, but shines brightly and gives out sparks when strongly heated. On charcoal, with soda, a deposition of zinc; soluble in h. acid with strong extraction of chlorine. Chem. com. 66 to 69 iron and 15 to 18 manganese peroxide (or in part protoxides), and 10 to 17 zinc oxide. Franklin and Sterling in New Jersey.

Dystuite, from Sterling, N. J.; dark or yellowish-brown; vitreous; G. = 4-5; contains 30 per cent. alumina. Isophane, G. = 5-01, seems also Franklinite.

**337. Hematite, Specular Iron.—Fe.

Rhombohedral; R = 86°. Crystals rhombohedral, prismatic, or tabular, of R. OR, OR. R (fig. 213), R. = ½ R ∞ P2, R. = ¼ P2. OR, ¼ P2. R. = ¼ R, (or n, P, s), (fig. 214).

Macles with parallel axes, and mostly intersecting. Cleavage, R and OR, but seldom distinct; fracture conchoideal or uneven; brittle. H. = 5-5...6-5; G. = 5-1...5-3. Opaque, or in very thin laminae translucent and deep blood-red. Metallic; iron-black to steel-gray, but often tarnished, also red; streak cherry-red or reddish-brown. Usually weak magnetic. B.B. in the red flame black and magnetic; slowly soluble in acids. Chem. com. 70-03 iron and 29-97 oxygen, but sometimes contains oxide of titanium, chrome, or silica.

Specular Iron Ore, varieties with crystalline structure and high metallic lustre, includes micaceous iron, thin lamellar, and red iron froth, finer or scaly. The Red Hematite or red iron, with inferior lustre, lower specific gravity (4-5...4-9), and hardness (3...5), and deeper blood-red or brownish-red colours; comprises the fibrous red iron, reniform, botryoidal, and stalactitic, often with an irregular concentric structure; the compact and ochrey iron ores, more earthy or minute; the redbile or red chalk, still more earthy, and used as a drawing material; and the jaspery, columnar, and lenticular clay iron, mere impure varieties.

Crystals, Elba, St Gotthardt, Framont in the Vosges, Arendal, Langbanshytta, Tilkerode in the Harz, Altenberg, Capas in Brazil, Katherinenburg and Nischnie-Tagilsk. Micaceous, Zorge in the Harz, Tincroft in Cornwall, Tavistock in Devonshire, Wales, Cumberland, and Birnam in Perthshire; also in Auvergne, on Vesuvius, Etna, and Stromboli. The Red Hematite, the Harz, Ulverstone in Lancashire, near Edinburgh, and in many other parts of Britain. A most abundant ore of iron.

Martite.—Tesseral, O, O. = O and O. = O. H. = 6; G. = 4-6...5-33. Iron-black, with reddish-brown streak. Either pseudomorphs after magnetite, or a dimorphous form of hematite. Brazil, Monroe in New York, Framont, and Auvergne.

338. Ironite.—(Ir, Os, Fe) (Ir, Os, Fe).

Tesseral; O; but in fine iron black scales, with strong metallic lustre, which mark paper. G. = 6-506. Strongly magnetic. B.B. fused with nitre gives out the odour of osmium; insoluble in acids. Chem. com. 62-86 peroxide of iridium, 10-30 osmium protioxide, 12-50 iron protioxide, 13-7 chrome oxide, with traces of manganese. Ural, with platinum.

*339. Limonite, Brown Iron Ore.—2 Fe + 3 H.

Fine fibrous, in spherical, reniform, and stalactic masses; also compact and earthy. H. = 5...5-5; G. = 3-4...3-95. Opaque; lustre weak silky, glimmering, or dull. Colour brown, especially yellowish, clove, hair, and blackish-brown, also yellow and green; streak yellowish-brown. In the closed tube yields water, and the powder becomes red. B.B. in the outer flame red on ignition; in the inner flame thin splinters fuse to a black magnetic glass. Chem. com. 85-6 peroxide of iron (= 60 iron), and 14-4 water; but occasionally with silica, alumina, or phosphoric acid. Harz, Thuringia, Siegen near Bonn, Naussau, Styria, Carinthia, Pyrenees, Siberia, Brazil, and the United States; in Britain in Cornwall, at Clifton near Bristol, Sandlodge in Zetland, and in many other places. A valuable ore of iron, the iron usually uniting hardness with tenacity. Stilposiderite, Lepidokrohite, and Yellow ochre seem partly this mineral, partly Goethite, or mixtures.

Bog-Iron Ore is also an hydrated oxide of iron, with no definite composition, and often containing thirty to fifty per cent. of impurities. Phosphoric acid to 11 per cent. Occurs chiefly in bogs, meadows, and lakes, as in North Germany, Sweden, and Britain; especially the northern and western islands of Scotland.

*340. Goethite, Pyrrhosiderite.—4 Fe + H.

Rhombic; P with polar edges 121° 5' and 126° 18', ∞ P(g) 94° 53', ∞ P2(d) 130° 40', P(x) (b) 117° 30', with ∞ P∞ (M) and P (P), (fig. 215); also columnar, fibrous, or scaly. Cleavage, brachydialgonal very perfect; brittle. H. = 5...5-5; G. = 3-8...4-4. Opaque, or in fine lamellae, translucent, and hyacinth-red; lustre adamantine or silky. Colour yellowish, reddish, or blackish-brown; streak brownish or reddish-yellow. In the closed tube the powder yields water, and becomes reddish-brown. B.B. in the ox. flame also brown; in the red. flame black and magnetic; difficultly fusible; soluble in h. acid, often leaving a little silica. Chem. com. 90 peroxide of iron and 10 water, with silica and manganese peroxide. Foliated, Eiterfeld near Siegen. Crystals, Lostwithiel in Cornwall, and Clifton near Bristol. Capillary, Prizbram, Hüttenberg in Carinthia, and Norway. Compact, Mineralogy.

Saxony, the Pyrenees, Ural, North America, and many other localities.

**Turgosite**, with 94-15 peroxide of iron and 5-85 water; compact reddish-brown; \( G = 3.54 \ldots 3.74 \); Turginsk in the Ural; is probably a mixture.

*341. Ilmenite*, Titanitic Iron.—(Fe, Ti).

Rhombohedral, and isomorphous with hematite, but sometimes tetartohedral; \( R = 86^\circ (85^\circ 40' \text{ to } 86^\circ 10') \). Crystals tabular or rhombohedral, of OR (a) and R, with \( -\frac{1}{2} R (e), -2 R (d), \text{ and } \frac{1}{2} (P 2) (b), \text{ (fig. 216)} \). Also in macles, granular or foliated, or in loose grains. Cleavage, basal more or less perfect, and rhombohedral \( R \) less distinct; fracture conchoidal or uneven. \( H = 5 \ldots 6; G = 4.66 \ldots 5 \). Opaque; semimetallic. Iron-black, often inclining to brown, rarely to steel-gray; streak generally black, but sometimes reddish-brown. Slightly or not at all magnetic. B.B. infusible alone, but with salt of phosphorus in the red, flame a red glass; soluble, but often with much difficulty in h. acid. Chem. com. peroxide of iron with 8 to 53 blue oxide of titanium. Ilmen Mountains; Gastine in Salzburg (Kobdelophan); Egersund in Norway; near Arendal (Hystatit); Menaccan in Cornwall (Menaccanite); Bourg d'Oisans in Dauphiné (Crichtonite). Moksite is the same, or connected.

**Iserine**, or magnetic iron sand, in cubes, octahedrons, and dodecahedrons, generally with rounded edges or in loose grains; strongly magnetic in chemical action and composition; resembles ilmenite, but is perhaps only magnetite mixed with peroxide of titanium. Iserweise in Bohemia, the Eifel, Auvergne, near Rome and Naples; also in Northern Germany; Cornwall, sands of the Don in Aberdeenshire, and Loch of Tristan in Zetland.

**Family II.—Tin Ore.**

Crystallization tetragonal, rhomboic, or rarely monoclinohedral, with prismatic forms. Hardness 5-5...6-5 or 7. Gravity 3-4...4-3 in the titanium compounds, 4-6...8 in the remainder. Mostly not soluble, or very difficultly, in acids, and also B.B. very difficultly, or not fusible. Colours dark, as black, brown, or red. Lustre resinous, semimetallic, or adamantine. Occur chiefly in the older crystalline strata, or in granite and syenite.

*342. Cassiterite*, Tin Ore.—Sn.

Tetragonal; \( P = 87^\circ 5', P = 67^\circ 50' \). Crystals \( \propto P \); \( \propto P (q), P (s), \propto P (l), \text{ or with } P (P), \text{ (fig. 217)} \); and also \( \propto P (r), \text{ and } P (z), \text{ (fig. 218)} \). Macles very common, combined by a face of \( P \propto \), with the chief axis \( 112^\circ 10' \) (figs. 219, 220); also granular or fibrous (wood tin), or in rounded fragments and grains (stream tin). Cleavage, prismatic along \( \propto P \) and \( \propto P \propto \), rather imperfect; brittle. \( H = 6 \ldots 7; G = 6.8 \ldots 7 \). Translucent or opaque; adamantine or resinous. White, but usually gray, yellow, red, brown, and black; streak white, light-gray, or brown. B.B. in the forceps infusible; on charcoal, in the inner flame, more easily with soda, reduced to tin. Not affected by acids. Chem. com. 79 tin and 21 oxygen, but often mixed with peroxide of iron or manganese, tantalic acid, or silica. Cornwall, Bohemia, Saxony, Galicia in Spain, and Portugal; also Silesia, the Haute Vienne in France, Greenland, Sweden, Russia, North and South America, Malacca, and Banca. The only ore of tin. The produce of the Cornish mines is about 100,000 cwt annually.

**Stannite**.—Compact; brittle. \( H = 6.75; G = 3.5 \). Translucent only on thinnest edges; weak resinous. Yellowish white to yellow. B.B. infusible. Chem.com. 36-5 tin oxide with silica and alumina. Probably a mixture. Cornwall.

*343. Wolfram*.—(Fe, Mn) W.

Rhombe; \( \propto P 101^\circ 45', \frac{1}{2} P \propto 123^\circ 57', \propto P \propto 98^\circ 27' \). Crystals \( \propto P (r), \frac{1}{2} P \propto (t), \propto P \propto (M), \propto P \propto (u), \text{ (fig. 221)} \). Macles rather common, also columnar, lamellar, or coarse granular. Cleavage, brachydiagonal very perfect; macrodiagonal imperfect; fracture uneven. \( H = 5 \ldots 5.5; G = 7.1 \ldots 7.5 \). Opaque; resinous, metallic-adamantine on the cleavage. Brownish-black; streak reddish-brown to black. Sometimes weak magnetic. B.B. on charcoal fuses to a magnetic globule covered with small crystals; soluble in warm h. acid, leaving a yellow residue. Chem. com. 76 tungstic acid, 9-5 to 20 protoxide of iron, and 4 to 15 protoxide of manganese, in some with a little lime or magnesia. Altenberg, Geyer, Ellenfriedersdorf, Schlakenwald, Zinnwald, the Harz, Cornwall, near Redruth, Roma in the Hebrides; also the Ural, Ceylon, and North America.

344. Columbite*, Niobite.—(Fe, Mn) Nb.

Rhombe; \( \propto P 100^\circ 40', 2 \propto P 59^\circ 20' \). Tabular, or broad prismatic (fig. 222). Macles with chief axes at \( 59^\circ 20' \); also foliated or granular. Cleavage, brachydiagonal very distinct, macrodiagonal less so, and basal imperfect. \( H = 6; G = 5.4 \ldots 6.4 \). Opaque; metallic adamantine. Brownish or iron-black; streak reddish brown or black. B.B. infusible; not affected by acids. Chem. com. 14 to 17 protoxide of iron, 3-7 to 4-8 protoxide of manganese, and 78 to 81 niobic (or columbic) acid, with a little oxide of tin or copper. Middletown and Haddam in Connecticut, and Chesterfield in Massachusetts; Rabenstein near Bodenmais, and Ilmen Mountains.

345. Samarskite*, Uranotantalite, Yttroilmenite.

Rhombe; isomorphous with columbite; mostly flat, somewhat polygonal grains. Fracture conchoidal; brittle. \( H = 5 \ldots 5; G = 5.625 \). Opaque; strong semi-metallic. Velvet-black; streak dark reddish-brown. B.B. fuses on the edges to a black glass. In the closed tube decrepitates, yields water, incandesces, and becomes brown. Soluble in h. acid with difficulty, but wholly to a greenish fluid. Chem. com. 56 niobic acid, 15 to 16 iron protoxide, 14 to 17 ura- Mineralogical Science.

346. Tantalite.—(Fe, Mn) Ta.

Rhombic; P with polar edges 126° and 112° 30', middle 91° 42'. Cleavages all very indistinct; fracture conchoidal or uneven. H. = 6...6.5; G = 7...8. Opaque; semimetallic, adamantine, or resinous. Iron-black; streak cinnamon or coffee brown. B.B. infusible; scarcely affected by acids. Chem. com. 7 to 14 protoxide of iron, 1 to 7 protoxide of manganese, and 67 to 84 tantalic acid, with tin oxide and lime. Kimito and Tammela in Finnland, Broddbo and Finbo near Falun.

Cassiterotantalite, varieties with much tin oxide, have G = 62...65, and with soda yield tin.

347. Yttriotantalite.—(Y, Ca, Fe, Ú) (Ta, W.)

Crystallization unknown; indistinct four or six sided prisms; also in grains and lamellae. Cleavage in one direction; fracture conchoidal or uneven. Opaque, or in thin splinters translucent. Three varieties are distinguished— (a) Black Y, iron-black, semimetallic, and greenish-gray streak; H. = 5.5; G = 5.5...4.2. (b) Dark or Brown Y, brownish-black, bright brown streak, vitreous or resinous. (c) Yellow Y, yellowish-gray, or brown, often striped or spotted; streak white; resinous or vitreous. H. = 5; G = 5.88. B.B. infusible, but become brown or yellow; not affected by acids. Chem. com. 57 to 60 tantalic acid, 1 to 8 tungstic acid, 20 to 38 yttria, 0.5 to 6 lime, 0.5 to 6 uranium peroxide, and 0.5 to 35 iron peroxide. Yterby, and near Falun.

348. Euxenite.—Ta, Ti, Y, Ce, Ca, H.

Monoclinohedric probably; also compact, with no trace of cleavage. Fracture imperfect conchoidal. H. = 6.5; G = 4.6. Opaque; thin splinters reddish-brown translucent; metallic vitreous. Brownish-black; streak reddish-brown. B.B. infusible; not affected by acids. Chem. com. uncertain. Jölster and Arendal in Norway.

349. Fergusonite.—(Y, Ce, Zr) Ta.

Tetragonal and hemiedric; P 128° 28' (fig. 223). Cleavage, traces along P; fracture imperfect conchoidal; brittle. H. = 5.5...6; G = 5.8...5.9. Translucent in thin splinters; semimetallic. Brownish-black; streak pale-brown. B.B. infusible. Chem. com. 48 tantalic acid, 42 yttria, 5 cerium protoxide, 3 zirconia, with tin oxide, uranium, and iron peroxide. Cape Farewell in Greenland.

Tyrite, brown, resinous or semimetallic; H. = 6.5; G = 5.5...5.36; Helle, near Arendal; is similar or identical. Azorite, minute, greenish or yellowish white tetragonal pyramids from the Azores, seems a tantalate of lime.

350. Spheke, Titanite.—Ca SiO₄ + Ca TiO₃.

Monoclinohedric; C = 85° 6'; P (I) 133° 54', P (x) 52° 21', P (y) 34° 27', OP (P), (xP) (q), (xP) (M), and (P2) (n) 136° 6'. Crystals horizontal prismatic or tabular, or very often oblique prismatic (figs. 224, 225). Macles frequent; also granular or foliated.

Cleavage, in many xP; in others (Poo) (r) 113° 30', imperfect. H. = 5...5.5; G = 3.4...3.6. Semitransparent or opaque; adamantine or often resinous. Brown, yellow, or green. B.B. fuses on the edges to a dark glass; with salt of phosphorus in the red flame reaction for titanic acid; wholly soluble in s. acid, which forms sulphate of lime. Chem. com. 313 silica, 40-4 titanic acid, and 28.3 lime, with 0 to 5 iron protoxide in the brown varieties. Dauphiné near Mont Blanc, St Gothard, Tyrol, Arendal, Sweden, Saxony, France, America, and the Ural; also Lake Laach and Vesuvius; in Scotland, in Criffell, near King's House, Ben Nevis, Strontian, Loch Ness, Aberdeenshire, Fetlar and Burra in Zetland.

Greenovite, flesh-red, from St Marcel in Piedmont, with much protoxide of manganese, is not distinct. Schorlomite, black shining; H. = 7...7.5; G = 3.78...3.86; from Arkansas, is related.

351. Brookite.—Ti.

Rhombic; P with polar edges 135° 37' and 101° 3', 90° 50' (fig. 226). Cleavage macrodiagonal. H. = 5.5...6; G = 3.86...4.2. Opaque or translucent; metallic adamantine. Yellowish, reddish, or hair-brown; streak yellowish-white. B.B. infusible; with salt of phosphorus forms a brownish-yellow glass. Chem. com. titanic acid, with 1 to 4 per cent. peroxide of iron. Bourg d'Oisans, Chamouni, and near Amstig in the Canton Uri, Miask, Magnet Cove in Arkansas (Arkansite); Snowdon and Tremadoc in North Wales.

*352. Rutile, Nigrine.—Ti.

Tetragonal; P 84° 40', Poo 65° 35'. Crystals ooP, ooPoo, P, and ooP3. P (fig. 227). Macles very common (like fig. 220) with chief axis at 114° 26'; also imbedded or granular. Cleavage, ooP and ooP perfect. H. = 6...6.5; G = 4.2...4.3. Translucent or opaque; metallic adamantine. Reddish-brown to red, also yellowish and black (Nigrine); streak yellowish-brown. B.B. unchanged alone; with borax in the ox. flame forms a greenish, in the red flame a violet glass; not affected by acids. Chem. com. titanic acid, with 1 to 5 per cent. or more peroxide of iron. Alps, in Spain, St Yrieux near Limoges, Norway, the Ural, Brazil, and North America; Craig Caileach near Killin, Ben-y-glo and Cranlarich in Perthshire, and Burra in Zetland. Used in painting porcelain to produce a yellow colour.

353. Anatase, Octedrite.—Ti.

Tetragonal; P 136° 36'. Crystals ooP (fig. 228), or P, ooP. Cleavage, basal and P both perfect; brittle. H. = 5.5...6; G = 3.8...3.93. Semi-transparent or opaque; metallic adamantine. Indigo-blue, almost black, red, yellow, or brown, rarely colourless; streak white. B.B. infusible; only soluble in warm con. s. acid. Chem. com. titanic acid with a little peroxide of iron, or rarely tin oxide. The Alps, as Bourg d'Oisans, Dauphiné, Valois, and Salzburg; Hof in Bavaria, at Slidre in Norway, Ural, Minas Geraes in Brazil, and in Cornwall.

354. Polymignite.

Rhombic; P with polar edges 136° 28' and 116° 22', P 109° 46'. Crystals long prismatic, rather broad, and vertically striated. Cleavage imperfect; fracture conchoidal. H. = 6.5; G = 4.806. Opaque; semimetallic. Iron-black; streak dark-brown. B.B. infusible alone, or with soda; soluble in con. h. acid. Analysis by Berzelins—46.30 titanic acid, 14.14 zirconia, 12.20 iron peroxide, 2.70 manganese peroxide, 5.00 cerium peroxide, 11.50 yttria, 4.20 lime (=9604). Fredriksvärn, Norway.

355. Polyerase.—Zr, Y, Fe, U, Ce, Ti, Ta.

Rhombic, six-sided tables, ooP 140°. Cleavage not observable; fracture conchoidal. H. = 5...6; G = 5...5.15. Opaque, or in very fine splinters translucent yel- lowish-brown. Black; streak grayish-brown. B.B. decrepitates violently, incandesces, and becomes grayish-brown, but is infusible; imperfectly soluble in warm h. acid, wholly in s. acid. Hitterö in Norway.

356. PERROWSKITE.—Ca Ti.

Tesseral; especially O O O, also O, O O. Cleavage hexahedral. H. = 5-5; G. = 4. Opaque, or translucent on the edges; adamantine. Grayish or iron-black, or dark reddish-brown. B.B. infusible; slightly affected by acids. Chem. com. 58-9 titanic acid; and 41-1 lime, with 2 to 5 iron protoxide. Slatoust, Kaiserstuhl in Baden.

357. AERCHYNYTE.—(Ce, La, Fe) (Nb, Ti) + Ce (Nb, Ti).

Rhombic; P 127° 19', P 73° 44'. Crystals long prismatic (fig. 229). Cleavage, only in traces; fracture imperfect conchoidal. H. = 5...5-5; G. = 4-9...5-1. Opaque; submetallic or resinous. Iron black or brown; streak yellowish-brown. B.B. swells and becomes yellow or brown, but is infusible; not soluble in h. acid, partially in con. s. acid. Mask in the Urals.

358. MENGITE.—Fe, Zr, Ti.

Rhombic; P 136° 20'. The crystals small, prismatic; fracture uneven. H. = 5...5-5; G. = 5-48. Opaque; semi-metallic. Iron-black; streak chestnut-brown. B.B. infusible, but becomes magnetic; almost wholly soluble in warm con. s. acid. Ilmen Mountains.

359. PECHURANE.—Pitch-Blende.—Ü Ü Ü.

Tesseral; O; also granular, reniform, columnar or lamellar. H. = 5...6; G. = 6-5 or 7-9...8. Opaque; imperfect metallic or resinous. Grayish, greenish, or brownish-black; streak greenish-black. B.B. infusible; not soluble in h. acid, but easily in warm n. acid. Chem. com. proto-peroxide of uranium, 84-78 uranium, and 15-22 oxygen, but with lead, iron, arsenic, lime, magnesia, silica, and other impurities. Some contain vanadium, others also selenium (Gummierz; H. = 2-5...3). Pittinerz; olive-green streak; H. = 3-0...3-5; G. = 4-8...5-0; and Coracite, from Lake Superior, seem mixtures. Johann-Georgenstadt, Marienberg, Annaberg, Prizbram, Rezbanya, and near Redruth in Cornwall. Used in porcelain-painting.

360. PLATTENHITE.—Pb.

Hexagonal; P 6P. P. Cleavage indistinct; fracture uneven; brittle. G. = 9-39...9-44. Opaque; metallic adamantine. Iron-black; streak brown. Chem. com. 86-2 lead and 13-8 oxygen, with trace of sulphuric acid. Leadhills in Scotland.

**Family III—Manganese Ores.**

Crystallization rhombic, tetragonal, and monoclinohedric. Crystals often prismatic. H. = 1-7; G. = 2-3...5. Opaque; lustre more or less perfect metallic. Colour black or brown. B.B. infusible, mostly give out much oxygen, and do not become magnetic; soluble in hydrochloric acid, with fumes of chlorine. The solution, saturated with carbonate of lime and filtered, gives, with chloride of lime, a copious dark-brown precipitate which acts like manganese oxide. Occur chiefly in veins in the older rocks, often along with barytes.

*361. PYROLUSITE.—Mn.*

Rhombic; P 93° 40'; P 140°. Crystals short, prismatic, or pointed (fig. 230); generally massive or reniform, and radiating, fibrous, earthy, or compact. Cleavage, P, also macro- and brachy-diagonal; rather brittle or friable. H. = 2...2-5; G. = 4-7...5. Opaque; semimetallic or silky. Dark steel-grey, bluish, or iron-black; streak black and soiling. B.B. infusible, loses oxygen, and becomes brown; soluble in h. acid, with large evolution of chlorine. Chem. com. 63-6 manganese and 36-4 oxygen. Ilmenau, Ilfeld, Goslar, Johann-Georgenstadt; also France, Hungary, Brazil, Cornwall and Devon. Used for producing oxygen, chlorine, and chloride of lime, removing the brown and green tints in glass, in painting glass and enamel-work, and for glazing and colouring pottery.

**Varvite.**—With 5 water, pseudomorphs after calc-spar; also crystals with P = 99° 36', or columnar, and fibrous. G. = 4-5...4-6. Semimetallic. Iron-black to steel-grey; streak black. Warwickshire.

362. POLLANITE.—Mn.

Rhombic; P 92° 52', P 118°. Crystals generally short, prismatic, and vertically striated; also granular. Cleavage, brachydiagonal perfect. H. = 6-5...7; G. = 4-8...4-88. Opaque; weak metallic. Light steel-grey. B.B. acts like pure hyperoxide of manganese. Chem. com. identical with pyrolusite, which seems thus a less hard variety or product of decomposition. Platten, Schneeberg, and Johann-Georgenstadt.

*363. MANGANITE.—Mn + H.*

Rhombic, sometimes hemihedric; P (M) 99° 40', P 118° 42', P (e) 114° 19'; also P 3(g), P 2(r), P 2(m), and P 2(n), (fig. 231). Crystals prismatic, vertically striated, and in bundles; also columnar or fibrous, rarely granular. Cleavage, brachydiagonal very perfect, basal and P less perfect; rather brittle. H. = 3-5...4; G. = 4-3...4-4. Opaque; imperfect metallic. Dark steel-grey to iron-black, or often brownish-black and tarnished; streak brown. B.B. infusible; soluble in warm con. s. acid. Chem. com. 89-9 manganese peroxide and 10-1 water. Ilmenau, in the Harz, Thuringia, Christiansand in Norway, Undenæs in Sweden, Nova Scotia, and Dannestrand near Aberdeen.

364. HAUSMANITE.—Mn + Mn, or Mn² Mn.

Tetragonal; P 117° 54', P 99° 11'. Crystals P or P, §P. Macles common (fig. 77); also granular. Cleavage, basal rather perfect, less distinct P and P; fracture uneven. H. = 5-5; G. = 4-7...4-8. Opaque; strong metallic. Iron-black; streak brown. B.B. like peroxide of manganese; soluble in h. acid, with escape of chlorine; powder colours con. s. acid bright-red in a short time. Chem. com. 31 protoxide and 69 peroxide of manganese, or 72-4 manganese and 27-6 oxygen. Ilmenau, and near Ilmenau.

365. BRAUNITE.—Mn.

Tetragonal; P 108° 39' ; hence almost an octahedron. Crystals P and P, OP. Cleavage, P rather perfect; brittle. H. = 6...6-5; G. = 4-818. Opaque; imperfect metallic. Colour and streak dark brownish-black. B.B., and with acids like manganite. Chem. com. 70 manganese and 30 oxygen. Elgersburg, Oehrenstock, Ilmenau, and St Marcel (Marceline).

366. PEILOMELANE.—(Mn, Ba, K, Cu), Mn + H.

Massive, botryoidal, or stalactitic. Fracture conchoidal or uneven. H. = 5-5...6; G. = 4-1...4-2. Opaque; dull or glimmering. Iron-black or bluish-black; streak brownish-black and glistening. B.B. infusible. Chem. com. 4-7 to 11 protoxide of manganese; 80 peroxide (but 20 to 50 mixed), 6 to 16 baryta, 2 to 5 potash, 0 to 1 copper, and 0-5 cobalt protoxide; and thus a mixture. Schneeberg, Ilmenau, France, Vermont, Cornwall, and Devon.

367. CREDNERITE.—Cu Mn².

Monoclinohedric; granular, foliated. Cleavage, basal very distinct, prismatic imperfect. H. = 4-5...5; G. = 4-9...5-05. Opaque; metallic. Iron-black; streak brownish- Mineralogy.

Black. B.B. very thin folie scarce fusible on the edges; with salt of phosphorus in the inner flame forms a glass first green, then copper-red; in h. acid it forms a green solution. Chem. com. 42:35 copper protoxide and 57:15 peroxide of manganese. Friedrichsroda in Thuringia.

368. Cutreous Manganese.—(Mn, Cu) Mn²⁺ + 2 H₂O.

Amorphous; botryoidal, stalactitic, or earthy. Rather brittle or friable. H. = 3:5 or less; G. = 3:1...3:2. Opaque; vitreous. Black, inclining to brown or blue; streak similar. Gives off much water in the closed tube. B.B. fusible, and yields copper. Contains 14 to 17 copper protoxide, 1:6 barita, 2:5 lime, 0:2 to 0:6 protoxide of cobalt and nickel, 15 to 17 water, and other substances; thus scarcely a true species. Silesia, Saxony, the Harz, and Cornwall.

Black copper, with 28 iron peroxide, 29:5 water, is similar. Harz.

369. Earthy Cobalt.—(Co, Cu) Mn²⁺ + 4 H₂O.

Amorphous; reniform, sectile. H. = 1...1:5; G. = 2:1...2:2. Opaque; dull. Bluish or brownish-black; streak black, shining, and leaves a mark. B.B. infusible. Contains about 20 cobalt protoxide, 4:5 copper protoxide, and 21 water. Saalfeld, Glückebrunn, Riechelsdorf, and Alderley Edge in Cheshire. Horn-cobalt, Siegen, is a mixture with quartz.

*370. Wad.—Mn (Ca, Ba, K) Mn³⁺ + 3 H₂O.

Massive; reniform, stalactitic, or froth-like; also scaly, earthy, or compact. Very soft and sectile (rarely brittle, and H. = 3); G. = 2:3...3:7; or porous, and swims on water. Opaque; semimetallic, and shining or dull. Colour and streak brown or black. B.B. like peroxide of manganese; soluble in h. acid. Chem. com. very uncertain. Saxony, Harz, France, Devonshire, and Cornwall. Groroilite is a variety, and Newkirkite related.

Family IV.—Ochres.

The following substances, chiefly products of decomposition, and all compact, earthy, or disseminated, and scarcely true mineral species, may be described here:

371. Cobalt-ochre, Earthy Cobalt.—Fe, As, Co, Ca, H₂O.

H. = 1...2; G. = 2...2:65. Yellowish-gray or brown to liver-brown; streak brown or yellowish-gray and shining. In the closed tube yields water. B.B. emits odour of arsenic, and fuses to a black magnetic slag. Saalfeld, Riechelsdorf, Dauphiné, and other localities.

372. Molybdena-ochre.—Mo.

Opaque; dull. Straw, sulphur, or orange yellow. B.B. fuses and smokes; soluble in h. acid. Sweden, Norway, the Tyrol, and on Coryby, near Loch Creran in Scotland.

373. Bismuth-ochre.—Bi.

Very soft and friable. G. = 4:36...4:7. Opaque; dull, or glimmering. Straw-yellow to light-gray or green. B.B. fusible and easily reduced; easily soluble in nitric acid. Schneeberg, Siberia, and St Agnes in Cornwall.

374. Antimony-ochre.—Sb, H₂O.

Soft and friable. G. = 3:7...3:8. Opaque; dull or glimmering, with glistening streak. Yellow, yellowish-gray, or white. B.B. easily reduced. Harz, Hungary, Saxony, France, Spain, and Padstow in England.

375. Stibnite.—Sb, H₂O.

H. = 3:5; G. = 5:28. Resinous or dull. Yellowish-white or yellow. B.B. not reduced alone, but easily with soda. Chem. com. 75 antimony, 20:5 oxygen, and 5:5 water. Kremnitz, Felssbanya, and Mexico.

376. Tungsten-ochre.—W.

Soft. Opaque; dull. Yellow or yellowish-green. Soluble in caustic ammonia. Huntington in North America.

377. Uranium-ochre.—U, H₂O.

Sectile, soft, and friable. Opaque; dull. Straw, sulphur, or orange yellow. In the closed tube yields water, and becomes red. B.B. in the red flame becomes green, but does not fuse; easily soluble in acids. Joachimsthal, Johann-Georgenstadt, and St Symphorien in France.

378. Minium (Native).—Pb + 2 Pb.

H. = 2...3; G. = 4:6. Opaque, dull or weak resinous. Aurora-red; streak orange-yellow. B.B. fuses easily, and reduces; in h. acid loses its colour, and changed into chloride of lead. Chem. com. 90:7 lead and 9:3 oxygen. Schlangenberg in Siberia, Badenweiler, Anglesea, Grassington Moor and Weirdale in Yorkshire.

379. Lead-ochre.—Pb.

G. = 8:0. Opaque; dull. Sulphur or lemon yellow. Poocatepetl in Mexico.

380. Chrome-ochre.—Cr.

Opaque, or translucent on the edges; dull. Grass-green to siskin or yellowish green. B.B. infusible; soluble to a green fluid in solution of potash. Unst in Zetland, Creuzat in France, and Sweden. Wolchoonskoite, emerald or blackish green, from Okhansk in Perm, is similar.

381. Tellurite.—Te.

Spherical, and radiated fibrous. Yellowish or grayish-white. Siebenbürg.

Family V.—The Red Copper Ores.

Tesseral and hexagonal. H. = 3:5...4:5; G. = 5:4...6. Translucent; metallic. Red or dark-gray. Soluble in acids, and B.B. fusible, except zincite. Are oxides of copper or zinc.

*382. Cuprite, Red Copper Ore.—Cu.

Tesseral; O. = O, and O = O; granular or compact. Cleavage, octahedral rather perfect; brittle. H. = 3:5...4; G. = 5:7...6. Translucent or opaque; metallic-adamantine. Cochineal to brick red, with a lead-gray tarnish; or crimson in transmitted light; streak brownish-red. B.B. on charcoal becomes black, fuses, and reduced; soluble in acids and ammonia. Chem. com. 88:9 copper and 11:1 oxygen. Siberia, the Bannat, Chessy near Lyons, Linares in Spain, and in the Huel Gorland, Huel Muttral, Carvath, and United Mines in Cornwall.

383. Chalcotrichite.

Rhombic or tesseral; in fine capillary crystals (prisms or cubes). Cochineal and crimson red. In other characters like cuprite. Rheinbreitenbach, Moldawa, and Huel Gorland, Carrharack, and St Day, in Cornwall.

Tile-ore.—Reddish-brown, or brick-red and earthy. Chem. com. suboxide of copper, mixed with much peroxide of iron and other substances. Bannat, Thuringia, Cornwall, and Shropshire.

384. Tenorite.—Cu.

Hexagonal, in thin tables; also fine scaly or earthy. Translucent and brown; metallic. Dark steel-gray or black. On lava, Vesuvius.

385. Zincite, Red Zinc.—Zn.

Hexagonal; granular or foliated. Cleavage, basal and O P very perfect. H. = 4...4:5; G. = 5:4...5:6. Translucent on the edges; adamantine. Blood or hyacinth red; streak orange-yellow. B.B. infusible, but phosphoresces. Chem. com. 80:26 zinc and 19:74 oxygen, but with 3 to 12 manganese peroxide. Franklin and Sterling in New Jersey. Ore of zinc.

Family VI.—The White Antimony Ores.

386. Valentinite, White Antimony.—Sb.

Rhombic; O P 137°, P 70°. Crystals O P O. P (fig. 232); broad prismatic, or long tabular; also granular, columnar, or foliated. Cleavage, O P very per- **MINERALOGY**

**387. SENARMONTITE.—Sb.** Tesseral; O; also massive. Cleavage, O imperfect. G. = 5-22...5-30. Transparent to translucent; brilliant resinous or adamantine. White or gray. B.B. and chem. com. like valentinite. Sensa, near Constantine in Algeria, Perneck in Hungary.

**388. CERVANTITE.—Sb.** Acicular or incrusting. G. = 4-1. Resinous. Yellow or white. B.B. infusible, but reduced on charcoal; soluble in h. acid. Chem. com. 79-5 antimony, 20-5 oxygen. Cervantes in Spain, Auvergne, Hungary, and Pereta in Tuscany.

**389. ARSENITE.—As.** Tesseral; O; usually capillary, flaky, or pulverulent. Cleavage octahedral. H. = 1-6 (3, Breit); G. = 3-6...3-7. Translucent; vitreous. Colourless and white. Tastes sweetish astringent; highly poisonous. B.B. in closed tube sublimes in small octahedrons; on charcoal volatilizes with strong smell of garlic. Chem. com. arsenious acid, with 75-76 arsenic and 24-24 oxygen. Andreasberg, Joachimsthal, Kapnik, Alsace, and Pyrenees.

**ORDER V.—NATIVE METALS.**

Form only one family. Crystallization either tesseral in regular octahedrons, as gold, silver, copper, and lead; or rhombohedric, with R = 86° to 88°; as antimony, arsenic, tellurium, and bismuth (tin is tetragonal). H. ranges from 1-5 in lead to 6...7 in iridium; G. from 5-7 in arsenic to 23 in iridium. Some (platinum, palladium, iridium, and iron) are infusible; gold and the others easily fusible; antimony, arsenic, and tellurium, burn and fume.

They are all opaque, metallic lustre, and pure metallic colours (not lead-gray nor black); streak similar and shining. Are simple metals or their combinations.

**390. PLATINA.—Pt, Fe.** Tesseral; very rarely in small cubes, commonly in minute, flat, or obtuse grains and roundish lumps. Cleavage wanting; fracture hackly; malleable and ductile. H. = 4...5; G. = 17...19 (hammered 21-23). Steel-gray, inclining to silver-white. Sometimes slightly magnetic. Very difficultly or not fusible; in nitrochloric acid forms a red coloured solution. Chem. com. platina, but generally alloyed with 4 to 13 iron, 1 to 5 iridium, and many other metals. Found in diluvial deposits in Columbia, Brazil, and St Domingo; in the Ural; also in California, Canada, Borneo, the Harz, and France. The largest mass from South America weighs 1 lb. 9½ oz.; from the Ural, 18¼ lb. English avoidupois. Its hardness, infusibility, power of resisting acids, and other properties, render platina a very important material for chemical, mathematical, and philosophical instruments. In Russia also used for money.

**391. PALADIUM.—Pd.** Tesseral; in very minute octahedrons; mostly small grains or scales. Malleable. H. = 4-5...5; G. = 11-8...12-2. Light steel-gray or silvery-white. B.B. infusible; in nitric acid forms slowly a brownish-red solution. Chem. com.

**392. OSMIUM-IRIDIUM.—Ir, Os.** Hexagonal; P 124°; or rhombohedric, R 84° 52', OP . OP (fig. 233), more common in small flat grains. Cleavage, basal rather perfect. Slightly malleable. Not affected by acids.

(a) Osmiridium.—Tin-white. H. = 7; G. = 19-38...19-47. B.B. not altered. Analysis, 46-77 iridium, 49-34 osmium, 3-15 rhodium, 0-74 iron, and trace of palladium. Katherinenburg.

(b) Iridosmium.—Lead-gray. H. = 7; G. = 21-118 (G. Rose). B.B. on charcoal becomes black, with a very strong odour of osmium; in the flame of a spirit-lamp shines brightly and colours it yellowish-red. In one variety Berzelius found 25 iridium and 75 osmium, or Ir Os²; in another, 20 iridium and 80 osmium, or Ir Os³. Nischne Tagilsk, Ural, Brazil, and Borneo.

**393. IRIDIUM, PLATIN-IRIDIUM.—Ir, Pt.** Tesseral; O; also small rounded grains. Cleavage, traces; slightly malleable. H. = 6...7; G. = 21-57...23-46. Silver-white, inclining to yellow on the surface. B.B. unalterable; insoluble in acids, even the nitrochloric. Chem. com., by Svanberg's analysis, 76-80 iridium, 19-64 platinum, 0-89 palladium, and 1-78 copper. Nischne Tagilsk and Newjansk. Used in porcelain-painting.

**394. GOLD.—Au.** Tesseral; O, O O, O O, 3O3, O2; and other forms. Crystals small, often elongated, deformed, and indistinct; also capillary, wire-like, arborescent, and in plates and grains. Remarkably ductile and malleable. H. = 2-5...3; G. = 17-0...19-4. Gold-yellow to brass or bronze yellow. B.B. easily fusible; soluble in aqua regia, often with a precipitate of chloride of silver. The solution is yellow, and colours the skin deep purple-red. Chem. com. gold with silver to 38 per cent, and copper and iron under 1 per cent. In beds, veins, and alluvial deposits in many parts of the world,—the Ural, Brazil, California, Australia; in the sand of many rivers, as Rhine and Tagus; in Britain in many of the Cornish stream-works; in mineral lodes near Dolgelly, North Wales; in Scotland at Leadhills, Tyndrum, and Glen Coich, Perthshire; and in Ireland in Wicklow.

**395. SILVER.—Ag.** Tesseral; cubes and octahedrons; also O, 3O3, and O2. Crystals small and often misshapen; also capillary, filiform, arborescent, or tooth-like, and in leaves, plates, or crusts. Malleable and ductile. H. = 2-5...3; G. = 10-1...11-1. Silver-white, but often tarnished yellow, red, brown, or black. B.B. easily fusible; easily soluble in nitric acid; the solution colours the skin black. Chem. com. silver, often with copper, iron, gold (28 per cent.), platinum, antimony, and arsenic. Chiefly in veins, as at Andreasberg, Freiberg, Johann-Georgenstadt, and Kongsberg in Norway; Mexico and Peru; St Mewan, St Stephens, Huel Mexico, and Herland in Cornwall; and at Alva in Stirlingshire.

**396. ANTIMONY-SILVER, DISCRASITE.—Ag4Sb.** Rhombe; P with polar edges 132° 42' and 92°, OP 120° nearly. Crystals short prismatic or thick tabular, and vertically striated; maces united by a face of OP; often in stellar groups (fig. 234); also massive or granular. Cleavage, basal and P distinct; OP imperfect; rather brittle, and slightly malleable. H. = 3-5; G. = 9-4...9-8. Silver-white to tin-white, with a yellow or blackish tarnish. B.B. fuses easily; fumes, staining the charcoal white, and leaves a grain of silver; soluble in nitric acid. Chem. com. 78 silver and 22 antimony. Andreasberg, Allemont in Dauphiné, Spain, and Arqueras in Coquimbo. A valuable ore of silver.

397. Mercury, Native Quicksilver.—Hg. Fluid; but at -40° congeals, and forms tesserai crystals. G. =13-545 fluid, 15-612 solid. Bright metallic; tin-white. B.B. wholly volatile, or leaves a little silver. Chem. com. mercury, sometimes with a little silver. Idria, Almaden, Wolfstein, and Morsfeld on the Rhine, the Harz, Peru, China, and California.

398. Amalgam.—Ag Hg², and Ag Hg³. Tesseral; O, with 2O₂, O, O₃, O₃, and O₃; also compact, or in crusts and plates. Cleavage, traces along O; rather brittle. H. =3...3.5; G. =13-7...14-1. Silver-white, and leaves the same colour on copper. In the closed tube yields mercury and leaves silver; easily soluble in nitric acid. Chem. com. 35 and 26% per cent. silver. Morsfeld and Moschellandsberg in Rhenish Bavaria, Hungary, Sala, Allemont, and Almaden. Arquerite in small octahedrons and arborescent; ductile and malleable. H. =2...2.5; G. =10-8. Chem. com. 86-5 silver. Forms the chief ore in the rich silver mines of Arqueras near Coquimbo.

399. Antimony.—Sb. Rhombohedric; R 87° 35', but very rarely crystallized, generally massive or spherical, and botryoidal. Cleavage, basal highly perfect; R perfect, and -R imperfect; rather brittle and sectile. H. =3...3.5; G. =6-6...6-8. Tin-white, with a grayish or yellowish tarnish. B.B. easily fusible; on charcoal burns with a weak flame; volatilizes and forms a white deposit. Chem. com. antimony, with a little silver, iron, or arsenic. Andreasberg, Prizbrum, Sala, and Allemont.

400. Arsenic-Antimony.—Sb As³. Rhombohedric; spherical or reniform. H. =3.5; G. =6-1...6-2. Tin-white to lead-gray, and tarnished with brownish-black. B.B. gives out a strong smell of arsenic. Chem. com. 35-2 antimony and 64-8 arsenic; but the two metals are isomorphous, and form indefinite compounds. Allemont; also Prizbrum, Schladming, and Andreasberg.

401. Arsenic.—As. Rhombohedric; R 85° 26' OR, R, -R (fig. 235); usually fine granular, rarely columnar, botryoidal, or reniform. Cleavage, basal perfect, R and -R imperfect; brittle. H. =3.5; G. =5-7...6-8. Whitish lead-gray, but in a few hours acquires a grayish-black tarnish. When broken or heated gives out arsenical odours. B.B. easily fusible, but on charcoal gives off dense white vapours, and may be wholly volatilized without fusing. Chem. com. arsenic, with some antimony, and traces of iron, silver, or gold. Andreasberg, Annaberg, Schneeberg, Marienberg, Freiberg, Joachimsthal, Kapnik, Orawitz, Allemont, St Marie aux Mines in Alsace, and Konigsberg; Tyndrum in Perthshire; also the Altai, North America, and Chili.

Arsenic-silver is a compound with silver; Kongsberg. Arsenic-glace, with 3 bismuth; H. =2; G. =5-36...5-39; dark lead-gray; takes fire at the flame of a candle, and burns; Marienberg. Arsenic is used in various pharmaceutical preparations and metallurgic processes.

402. Tellurium.—Te. Rhombohedric; R 86° 57' or R, R, -R; usually massive, and fine granular. Cleavage, O perfect, basal imperfect; slightly sectile. H. =2...2.5; G. =6-1...6-8. Tin-white. B.B. very easily fusible; burns with a greenish flame and much smoke, which forms a white ring with a reddish margin on charcoal. In con. s. acid forms a bluish-red solution. Chem. com. tellurium, with a little gold or iron. Facebay in Siebenburg.

403. Lead.—Pb. Tesseral, but only capillary, filiform, or in thin plates. Ductile and malleable. H. =1.5; G. =11-3...11-4. Bluish-gray with a blackish tarnish. B.B. very easily fusible; minerals on charcoal volatilizes and forms a sulphur-yellow coating; soluble in nitric acid. In lava on Madeira; also near Bristol and Kenmare in Ireland; in meteoric iron from Chili.

404. Tin.—Sn. This metal has not certainly been found native, though quoted from Cornwall. The fused metal crystallizes in regular octahedrons. That formed by galvanic action is described as tetragonal, with P 57° 13'.

405. Bismuth.—Bi. Rhombohedric; R 87° 40'. Crystals R, OR, but often misshapen, also aborescent or reticulated; often massive and granular. Cleavage, -2 R 69° 28', and basal perfect. Not malleable; very sectile. H. =2.5; G. =9-6...9-8. Reddish silver-white, often with a yellow, red, brown, or parti-colour tarnish. B.B. very easily fusible, even in the flame of a candle. On charcoal volatilizes, leaving a citron-yellow coating. Soluble in nitric acid. Chem. com. bismuth; sometimes with a little arsenic. Schneeberg, Annaberg, Marienberg, Joachimsthal; Bieber in Hanau; Wittichen; also Modum and Fahlum; near Redruth in Cornwall, Carick-Fell in Cumberland, and Alva in Stirlingshire.

406. Copper.—Cu. Tesseral; O, O, O, O. Crystals small, and generally irregular and deformed. Macles united by a face of O. Often filiform and arborescent, or in plates and laminae. Malleable and ductile. H. =2.5...3; G. =8-5...8-9. Copper-red, with yellow or brown tarnish. B.B. rather easily fusible, colouring the flame green; readily soluble in nitric acid. In large masses (200 tons) near Lake Superior, with native silver. Cornwall, near Redruth and the Lizard; Yell in Zetland, Chessey near Lyons, the Bannat, and Hungary; Faroe Islands, Siberia, China, Canada, Mexico, Brazil, and Chili.

407. Iron.—Fe. Tesseral; chiefly the octahedron. Cleavage hexahedral, but often mere traces; fracture hackly; malleable and ductile. H. =4.5; G. =7...7-8. Steel-gray or iron-black, often with a blackish tarnish. Very magnetic. B.B. infusible, or only in thin plates with a strong heat; soluble in h. acid. Two varieties are distinguished.

(a.) Telluric Iron.—In grains and plates, or disseminated. Almost pure iron, or contains carbon, graphite, lead, or copper, but not nickel. Said to occur at Gross Camdsdorf, Oule in Dauphine; in the gold sands of Brazil, the Ural and Olahpian; in veins in South Africa; also at Leadhills in Scotland, and in basalt in north of Ireland.

(b.) Meteoric Iron.—Steel-gray and silver-white; contains nickel, with cobalt, copper, and other substances. Polished and etched with nitric acid, the surface is marked by lines intersecting at 60° or 120°, named Widmanstätts figures. Has fallen from the sky in very many countries. Siberia, Brazil, North America, South Africa, Hungary, Britain and Ireland.

Order VI.—Sulphuretted Metals.

Crystallization often tesseral (ths), rhombic (ld), or hexagonal and rhombohedric (th), rarely other forms. H. =1...7; G. =3-4...9. Soluble in acids, and mostly B.B. easily fusible, many yielding fumes characteristic of sulphur, arsenic, or antimony. All (with one or two exceptions of blende) are opaque, and show metallic lustre and colour. Are all compounds of sulphur, arsenic, or antimony with metals. Occur frequently in veins, more rarely disseminated in rocks.

Family I.—Pyrites.

Crystallization tesseral, rhombic, or hexagonal, one tetragonal. Brittle, except bornite. H. =3...6.5, the iron pyrites being the harder, the copper ores the softer; G = 4·1...5·1, but sulphur compounds = 4·1...5·3, arsenic or antimony G = 5·1, sulphur with arsenic or antimony H = 6...6·5. Colour mostly yellow, becoming lighter or more gray in those with less sulphur. They are all soluble in nitric acid; solutions generally coloured, and all fusible, and give out fumes.

**408. Pyrite, Iron Pyrites.—Fe**.

Tesseral, and dodecahedral-semitesseral. The cube \( \propto O \), then \( O \propto \frac{O^2}{2} \) (fig. 236), and others (fig. 237), and macles (fig. 238). In druses or groups, spheroidal or reniform, and massive. Cleavage, hexahedral or octahedral very imperfect, or scarcely perceptible; brittle. H = 6...6·5; G = 4·9...5·2. Bronze-yellow, inclining to gold-yellow, often with a brown or rarely variegated tarnish; streak brownish-black. When broken emits a smell of sulphur. B.B. on charcoal burns with a bluish flame, and a strong smell of sulphur. In the red, flame fuses to a blackish magnetic bead. Soluble in nitric acid with deposition of sulphur; scarcely affected by h. acid. Chem. com. 46·7 iron and 53·3 sulphur. Very often contains gold, silver, or silicium, the gold occasionally in visible grains. Common in rocks of all ages and classes. Fine varieties, Elba, Cornwall, Persberg, Traversella; also Alston Moor and Derbyshire. Auriferous pyrites, Beresof, Marmato, Mexico, Aedelfors in Sweden, and many parts of England and Scotland. Used for the manufacture of sulphur, sulphuric acid, and alum.

**409. Marcasite, White Iron Pyrites.—Fe**.

Rhombic; \( \propto P \) 106° 5', \( \frac{1}{4} P \) 136° 54', \( P \propto 80° 20' \), \( P \propto 64° 52' \). Crystals like figs. 193 and 158; tabular or thin prismatic, or pyramidal. Macles frequent; also cockcomb-like groups, or spherical, reniform, and stalactitic. Cleavage, \( \propto P \) indistinct, \( P \propto \) traces; fracture uneven; brittle. H = 6...6·5; G = 4·65...4·9. Pale, or grayish bronze-yellow, sometimes almost greenish-gray; streak dark greenish-gray or brownish-black. B.B. and with acids acts like pyrite. Varieties are—Radiated pyrites, radiated, fibrous masses. Spear pyrites, macles, very fine at Littmitz, Prüzbram, Schenmichl, and Freiberg. Hepatic pyrites, or Leberkies, liver-brown, generally decomposing; Harz, Saxony, Sweden, Derbyshire, and Cornwall. Cockcomb pyrites, compound, comb-like crystals, often greenish, or with a brown tarnish; Derbyshire and the Harz. Wasserkies or Hydrous pyrites contains water; the Kyrosite copper and arsenic; Longchidite also arsenic.

**410. Pyrrhotite, Magnetic Pyrites.—Fe', or Fe'Fe''**.

Hexagonal; \( P \) 126° 50'. Crystals \( O \propto P \), or with \( P \) (fig. 239) tabular or short prismatic, but rare. Commonly massive, granular, or compact. Cleavage, \( SP \) imperfect, laminar structure along \( OP \); brittle. H = 3·5...4·5; G = 4·4...4·7. Colour between bronze-yellow and copper-red, with a pinchbeck-brown tarnish; streak grayish-black; more or less magnetic. Unaltered in the closed tube; in the open tube yields sulphurous fumes, but no sublimation. B.B. on charcoal on the red flame fuses to a black strongly-magnetic globule; soluble in h. acid. Chem. com. 63·65 iron and 36·35 sulphur, or 60·44 iron and 39·56 sulphur, in some with 2 to 3 nickel. Bodenmais, Fahlun, Königsberg, Andraesberg, Moel Eilion and Llanrwst in Caernarvonshire, Cornwall, Appin in Argyleshire, and Vesuvius; also in some meteoric stones.

**411. Leucoptyrite, Arsenical Pyrites, Löllingite.**

Rhombic; \( \propto P \) 122° 26', \( P \propto 51° 20' \), \( P \propto 86° 10' \). Crystals \( \propto P \), \( P \propto \) (fig. 240). Generally massive, granular, or columnar. Cleavage, basal rather perfect, \( P \propto \) imperfect; fracture uneven; brittle. H = 5...5·5; G = 7·0...7·4. Silver-white to steel-gray, with a darker tarnish; streak grayish-black. B.B. on charcoal emits a strong smell of arsenic, and fuses to a black magnetic globule. Chem. com. 27·2 iron and 72·8 arsenic, or 32·2 iron and 66·8 arsenic, but always 1·3 to 21 sulphur, and sometimes 13·4 nickel, and 5 cobalt. Reichenstein in Silesia; Schladdingen in Styria; Lölling in Carinthia; Andreasberg, in the Harz, and Fossum in Norway. Used for the manufacture of arsenious acid.

**412. Mispickel.—Fe S' + Fe As.**

Rhombic; \( \propto P \) 111° 12', \( \frac{1}{4} P \) 146° 23', \( P \propto 79° 22' \), \( P \propto 59° 2' \). Crystals \( \propto P \), \( P \propto \). Macles short prismatic or tabular; also massive, granular, or columnar. Cleavage, \( \propto P \) rather distinct; fracture uneven; brittle. H = 5...5·6; G = 6...6·2. Silver-white, almost steel-gray, with a grayish or yellowish tarnish; streak black. In the closed tube yields first a red then a brown sublimate of sulphuretted arsenic, and then metallic arsenic. B.B. on charcoal fuses to a black magnetic globule. Chem. com. 19·9 sulphur, 46·6 arsenic, and 33·5 iron, but some contain silver or gold, others 5 to 9 cobalt. Freiberg, Altenberg, Joachimsthal, Zinnwald, Schlackenwald, Andreasberg, Sweden, North America, and in many Cornish tin mines; Cobalt-mispickel, from Skutterud in Norway. Danate and Plinian seem the same mineral. Used as an ore of arsenic or of silver.

**413. Cobaltine.—Co S' + Co As.**

Tesseral and semitesseral, like pyrite; also massive or granular, disseminated. Cleavage, hexahedral perfect; brittle. H = 5·5; G = 6...6·3. Brilliant, silver-white, inclining to red, often with a grayish or yellowish tarnish; streak grayish-black. B.B. on charcoal fuses with strong smell of arsenic to a gray, weak magnetic globule; after roasting shows reaction for cobalt with borax. Chem. com. 39·5 cobalt (with 3·6 iron), 44·9 arsenic, and 19·2 sulphur. Skutterud in Norway, Tunaberg, Querbach in Silesia, Siegen, and St. Just in Cornwall.

Glaubodote.—Rhombic like mispickel. Dark tin-white; streak black; with 11·9 iron, 24·8 cobalt. Huasco and Valparaíso in Chili, Orawitz.

**414. Smaltine.—Co As.**

Tesseral; chiefly the cube and octahedron, the faces of the cube convex or cracked; also reticulated, reniform, or granular compact. Cleavage, traces along \( \propto O \) and \( O \); fracture uneven; brittle. H = 5·5; G = 6...6·3. Tin-white and steel-gray, with a dark-gray or iridescent tarnish; streak grayish-black. Gives out an odour of arsenic when broken. In the closed tube gives no sublimate of arsenic. B.B. fuses easily, with a strong smell of arsenic, to a white or gray magnetic globule. Chem. com. 71·4 arsenic and 28·6 cobalt, but with 3 to 19 iron and 1 to 12 nickel; others 1 to 3 bismuth. Schneeberg, Annaberg, Riechelsdorf, Allenton in Dauphiné; Tunaberg in Sweden; Chatham in Connecticut; Huel Spenn, Doalcouth, and Redruth in Cornwall. Gray Smaltine has 10 to 18 iron, and G = 6·9 to 7·3. Smalltine and cobaltine are used in preparing blue colours for painting porcelain and stoneware.

415. MODUMITE, Skutterudite.—Co₃ As₂.

Tesseral; O and ∞O∞, or granular. Cleavage, hexahedral distinct; fracture conchoidal or uneven; brittle. H. = 6; G = 6·74...6·84. Tin-white to pale lead-gray, sometimes with an iridescent tarnish. Lustre rather brilliant. In the closed tube it gives a sublimate of metallic arsenic; in other respects acts like smalltine. Chem. com. 79 arsenic, and 21 cobalt. Skutterud, near Modum in Norway.

416. LINNÉITE.—(Ni, Co', Fe') + (Ni", Co", Fe").

Tesseral; in octahedrons and cubes, or macle; also massive. Cleavage, hexahedral imperfect; brittle. H. = 5·5; G = 4·9...5·0. Silver-white inclining to red, often with a yellowish tarnish; streak blackish-gray. B.B. on charcoal fuses to a gray magnetic globule, bronze-yellow when broken. Chem. com. 11 to 53 cobalt, 0 to 42·6 nickel, 2 to 5 iron, and 1 to 15 copper. Bastnäs in Sweden, and Misen near Siegen.

417. SYEPORITE.—Co'.

Massive. Steel-gray or yellowish. G = 5·45. Chem. com. 65·2 cobalt, and 34·8 sulphur. Syepoor near Rajpootanah in North-West India. The Indian jewellers use it to give a rose colour to gold.

418. GRÜNAUITE, Saynite.

Tesseral; O and ∞O∞; also granular. Cleavage octahedral; brittle. H. = 4·5; G = 5·14. Light steel-gray inclining to silver-white, with a yellow or grayish tarnish. B.B. fuses to a gray, brittle, magnetic bead, yellow on the fracture, and colours the support yellow. The solution in nitric acid is green. Chem. com. nickel, bismuth, sulphur, iron, cobalt, copper, lead, in variable proportions. Grünau in Sayn-Altenkirchen.

419. GEISDORFITE.—(Ni, Fe) As+(Ni, Fe) S².

Tesseral; O, ∞O∞; usually granular. Cleavage, hexahedral rather perfect; fracture uneven; brittle. H. = 5·5; G = 5·6...6·13 (6·64 ?). Silver-white to steel-gray, with a grayish tarnish. In the closed tube decrepitates violently. B.B. fuses to a brittle, black, slag-like globule; partially soluble in nitric acid. Chem. com. 35·2 nickel (with 2·4 to 6 iron, 0 to 3 cobalt), 45·4 arsenic, and 19·4 sulphur; but others give different formula, with 10 to 15 iron and 14 cobalt. Harzgerode and Tanne, Schladming, Camsdorf, Loos in Helsingland, Sweden; also Spain and Brazil. Used as an ore of nickel.

Amoebite, Tombazite, and Wodanite, are similar.

420. ULLMANNITE.—Ni Sb + Ni S², or Ni² (Sb, As, S)².

Tesseral; O, ∞O∞, ∞O∞; usually granular. Cleavage, hexahedral perfect; fracture uneven. H. = 5...5·5; G = 6·2...6·5. Lead-gray to tin-white or steel-gray; with a grayish-black or iridescent tarnish. B.B. fuses with dense fumes, and slight odour of arsenic; soluble in con. nitric acid. Chem. com. 27·4 nickel, 57·5 antimony, and 15·1 sulphur, with 2 to 12 arsenic. Westerwald, Siegen, Harzgerode, and Loberstein.

421. BREITHAUPTITE.—Ni² Sb.

Hexagonal; P 112° 10'. Crystals, thin striated hexagonal tables of OP, ∞P. H. = 5; G = 7·54. Brilliant. Light copper-red, with violet-blue tarnish. B.B. fumes and fuses with great difficulty. Chem. com. 32·2 nickel, and 67·8 antimony, but mixed with 6 to 12 sulphuret of lead. Andreasberg.

422. NICKELINE, Copper Nickel.—Ni² As.

Hexagonal; P 86° 50'. Crystals, ∞P, OP (fig. 241), very rare and indistinct; also arborescent, reniform, or generally massive. Fracture conchoidal and uneven; brittle. H. = 5·5; G = 7·5...7·7. Light copper-red, with a tarnish first gray then blackish. It forms no sublimate in the closed tube. B.B. fuses with strong fumes to a white, brittle, metallic globule. Chem. com. 43·6 nickel and 56·4 arsenic, but with 0 to 2 cobalt, 0·2 to 9 iron, 0·1 to 4 sulphur, and 0 to 20 antimony. Freiberg, Schneeberg, Joachimsthal, Andreasberg, Chatham in Connecticut, Pengelly and Hucl Chance in Cornwall, and Leadhills in Scotland. Used as an ore of nickel.

Plakodite is a furnace product, not a native mineral.

423. RAMMELSBERGITE, White Nickel.—Ni As.

Tesseral; O, ∞O∞, ∞O∞; also fine granular or compact. Fracture uneven; brittle. H. = 5·5; G = 6·4...6·6. Tin-white, but first a gray, then a blackish tarnish, and loses its lustre. Yields an odour of arsenic when broken. In the closed tube forms a sublimate of metallic arsenic, and becomes copper-red. B.B. on charcoal fuses easily with much smoke, continues long ignited, becomes invested with crystals of arsenious acid, and leaves a brittle grain of metal. Chem. com. 28 nickel and 72 arsenic, but often with cobalt; and many smalltines belong to this species. Schneeberg, Riechelsdorf, Allemont.

424. CHLOANTHITE.—Ni As.

Rhombic; ∞P 123°...124°. G = 7·099...7·188. Colour tin-white, inclining to red on the fresh fracture. Otherwise like Rammelsbergite, with which it occurs. The names are sometimes transposed.

425. MILLERITE.—Ni'.

Rhombohedric; R 144° 8', in fine acicular prisms of ∞P 2. R. Brittle. H. = 3·5; G = 4·6, or 5·26, and 5·65. Brass or bronze-yellow, with a gray or iridescent tarnish. B.B. fuses easily to a blackish metallic globule, which boils and sputters. In nitro-chloric acid forms a green solution. Chem. com. 64·4 nickel and 35·6 sulphur. Johann-Gegenstadt, Joachimsthal, Prizibram, Camsdorf, Riechelsdorf, near St Austell in Cornwall, and at Merthyr Tydfil.

426. INVERARYITE, Eisennickelkies.—2 Fe' + Ni'.

Tesseral; massive and granular. Fracture uneven; brittle. H. = 3·5...4; G = 4·6. Light pinchbeck-brown, with darker streak. Not magnetic. B.B. acts in general like pyrrhotite; the roasted powder forms with borax in the red flame a black opaque glass. Chem. com. 36 sulphur, 42 iron, and 22 nickel; but mixed with pyrrhotite and chalcopyrite. Lillehammer in Southern Norway, near Inverary in Scotland.

*427. CHALCOPYRITE, Yellow Copper Ore, Copper Pyrites.

Tetragonal and sphenoïdal-hemihedral; ∞P (P) with polar edges 71° 20'; ∞P (b), 2 ∞P (c) 126° 11', OP (a), P and ∞P∞. Crystals generally small and deformed (fig. 242); macles very common, like fig. 243. Most commonly compact and disseminated; also botryoidal and reniform. Cleavage, pyramidal 2 P∞ sometimes rather distinct; fracture conchoidal or uneven. H. = 3·5...4; G = 4·1...4·3. Brass-yellow, often with a gold-yellow or iridescent (peacock copper ore) tarnish; streak greenish-black. B.B. on charcoal becomes darker or black, and on cooling red. Fuses easily to a steel-gray globule, which at length becomes magnetic, brittle, and grayish-red on the fractured surface. With borax and soda yields a grain of copper. Moistened with h. acid colours the flame blue. Chem. com. essentially 1 atom copper, 1 atom iron, and 2 atoms sulphur, with 34-5 copper, 30-5 iron, and 35 sulphur. The most abundant ore of copper. Anglesea (Parys Mine), Derbyshire, Staffordshire, Cumberland; Wicklow in Ireland; also in the Cornish mines (Gunnis Lake and St Austell); in Scotland in Kirkcudbrightshire and Wigtownshire, Tyndrum in Perthshire, Inverness-shire, Zetland, and other places. Of foreign European localities, Fahlun, Rorasa, Freiberg, Mansfeld, Goslar, Lauterberg, Musen, may be mentioned; also in Siberia, the United States, and Australia. The ores raised in Cornwall and Devon give 8 per cent. metal on the average; and that picked for sale at Redruth rarely yields 12, sometimes only 3 or 4 per cent. The richness of the ore may in general be judged by the colour; if of a fine yellow hue, and yielding readily to the hammer, it may be considered a good ore; but if hard and pale yellow, it is assuredly a poor one, being mixed with iron pyrites. From pyrite it is distinguished by yielding readily to the knife, by its tarnish, and by soon forming a green solution in nitric acid.

Cuban.—Cu Fe + 2 Fe. Tesseral in cubes or massive, with a hexahedral cleavage. G. = 4-02...4-04. B.B. very easily fusible, otherwise like chalcopyrite. Chem. com. 22-96 copper, 42-51 iron, and 34-78 sulphur. Bacaranao in Cuba.

*428. Bornite, Variegated or Purple Copper. Cu Fe.

Tesseral. Crystals, ∞ O ∞, and ∞ O ∞ O, but rare, and generally rough or uneven; also maclea. Mostly massive. Cleavage, octahedral very imperfect; fracture conchoïdal or uneven; slightly brittle, or almost sectile. H. = 3; G. = 4-9...5-1. Colour between copper-red and pinchbeck-brown, with very pale tarnish, especially steel-blue, inclining to red and green; streak grayish-black. B.B. acts like chalcopyrite; soluble in con. h. acid, leaving sulphur. Chem. com. 3 atoms copper, 1 atom iron, and 3 atoms sulphur, with 55-6 copper, 16-4 iron, and 28 sulphur, but often, especially when compact, mixed, and then 56 to 71 copper, and 6 to 17 iron. Crystals near Redruth and St Day in Cornwall; massive at Killarney in Ireland; also Norway, Sweden, Mansfeld, Silesia, Tuscany, and Chili. An ore of copper.

429. Domeykite.—Cu As.

Botryoidal, reniform, or massive. Fracture uneven or conchoïdal; brittle. H. = 3...3-5. Tin or silver white, inclining to yellow, with an iridescent tarnish. B.B. fuses easily with strong odour of arsenic; not affected by h. acid. Chem. com. 71-63 copper and 28-37 arsenic. Calabazo in Coquimbo and Copiapo in Chili.

Condurrite.—Massive, soft, and soils the fingers. Fracture flat conchoïdal. Colour brownish or bluish black. G. = 4-20...4-29. B.B. on charcoal fuses, with escape of arsenic vapours, to a globule, which, on cooling, cracks, swells, and falls to pieces. With soda and borax leaves a grain of copper. Seems an impure variety. Condurrow Mine and near Redruth in Cornwall.

430. Arsenimuret of Manganese.—Mn As.

Massive and botryoidal, granular or foliated. Fracture uneven; brittle. G. = 5-65. Grayish-white, with a black tarnish. B.B. burns with a blue flame, and emits fumes of arsenic; soluble in nitro-chloric acid. Chem. com. 42-75 manganese, 57-25 arsenic, with trace of iron. Saxony.

Family II.—Lead Glance.

Crystallization, chiefly tesseral; also rhombic and rhombohedric. H. = 1...2-5; rarely more; G. = 4-6...8-9, and mostly 5-5, or higher. Colours generally lead-gray, and more or less dark. All soluble in acids. B.B. all fusible, and mostly very easily, and easily reduced. They are compounds with sulphur, arsenic, or selenium; known by their fumes. Chiefly occur in veins.

*431. Galena, Sulphuret of Lead.—Pb.

Tesseral; ∞ O ∞, ∞ O; seldom 2O, and 2O2. Crystals, ∞ O ∞ O. Also massive and granular, compact, or lamellar. Cleavage, hexahedral very perfect; fracture scarcely observable; sectile. H. = 2-5; G. = 7-2...7-6. Lead-gray, with darker, or rarely iridescent tarnish; streak grayish-black. B.B. decrepitates, fuses, and leaves a globule of lead; soluble in nitric acid. Chem. com. 86-7 lead, and 13-3 sulphur, but usually contains a little silver,—ranging from 1 to 3, or 5 parts in 10,000; rarely 1 per cent. or more. Some contain copper, zinc, or antimony, others selenium, and others (the supersulphuret) probably free sulphur (2 to 8 per cent.). Most common ore of lead in many countries. Cornwall, Derbyshire (Castletown), Wales, Cumberland, Alston Moor, Durham (Altonhead); Isle of Man; Leadhills, Penland Hills, Linlithgow, Inverkeithing, Monaltire, Strontian, Islay, and many other places in Scotland. In 1855 the produce was,—England, 65,265 tons; Wales, 18,204; Isle of Man, 3573; Ireland, 2005; and Scotland, 1587 tons.

432. Cuprophilumite.—Cu Pb.

Tesseral; massive, with distinct hexahedral cleavage. Rather sectile and brittle. H. = 2-5; G. = 6-408...6-428. Blackish lead-gray; streak black. B.B. does not decrepitate; with soda gives a grain of metal. Chem. com. 65 lead, 19 copper, and 16-1 sulphur (with 0-5 silver). Chili.

433. Clausthalite.—Pb Se.

Tesseral; but massive and fine granular, with hexahedral cleavage. H. = 2-5...3; G. = 8-2...8-8. Lead-gray; streak gray. B.B. on charcoal fumes, smells of selenium, colours the flame blue, stains the support red, yellow, and white; and volatilizes, except a small remainder, without fusing. Chem. com. 72-7 lead (with 11-6 silver), and 27-3 selenium. Lerbach, Zorge and Tilkerode in the Harz.

Tilkerodite, with cobalt; G. = 7-7; colours borax glass smalt-blue. Lehrbackite; Lerbach and Tilkerode; with 17 to 45 mercury, seems a mixture.

434. Selengopperlead.—(Cu, Pb) Se.

Massive and fine granular. Sectile. H. = 2-5; G. = 7...7-5. Light lead-gray inclining to brass-yellow, or with a bluish tarnish; streak darker. B.B. like clausthalite, only some fuse slightly on the surface, others easily forming a gray metallic mass. Chem. com. 30 to 35 selenium, 47 to 64 lead, and 4 to 16 copper (with 0 to 1-3 silver). Tilkerode, Zorge, and near Gabel in Thuringia.

435. Onofrite.—Hg Se + 4 Hg S.

Massive, and granular. H. = 2-6. Blackish lead-gray or steel-gray; streak shining. In the closed tube wholly volatile with a black sublimate. With soda gives metallic mercury. Chem. com. 82-8 mercury, 66 selenium, and 106 sulphur. St Onofre in Mexico, Zorge in the Harz.

436. Tiemannite.—Hg Se, or Hg2 Se2.

Fine granular; brittle. H. = 2-5; G. = 7-1...7-4. Brilliant. Dark lead-gray. In the closed tube decrepitates, swells, fuses, and volatilizes to a black and brown deposit. Only soluble in nitro-chloric acid. Chem. com. 75 mercury, 25 selenium. Clausthal.

437. Naumannite.—Ag Se.

In thin plates and granular. Cleavage, hexahedral perfect. Malleable. H. = 2-5; G. = 8. Iron-black; splendid. B.B. on charcoal fuses; with soda a grain of silver; easily soluble in con. nitric acid. Chem. com. 73 silver and 27 selenium, with 4-91 lead. Tilkerode.

Silverphyllinglanz.—Massive, foliated; perfect cleavage; thin lamina flexible. H. = 1...2; G. = 5-8...5-9. Dark-gray. Chem. com. antimony, lead, tellurium, gold, and sulphur (Plattner). Deutsch-Pilsen in Hungary.

*438. Argentite, Sulphuret of Silver.—Ag.

Tesseral; ∞ O ∞, O, ∞ O, and 2O2 (fig. 244). Crystals generally misshapen, with uneven or curved faces; in druses, or linear groups; also arborescent, capillary, or in crusts. Cleavage, very indistinct traces along \( \alpha O \) and \( \alpha O' \); fracture uneven and hackly; malleable and flexible. \( H = 2...2\frac{1}{2} \); \( G = 7...7\frac{1}{2} \). Rarely brilliant; more so on the streak. Blackish lead-gray, often with a black, brown, or rarely iridescent tarnish. B.B. on charcoal fuses, intumesces greatly, and leaves a grain of silver; soluble in con- nitrile acid. Chem. com. 87 silver, and 13 sulphur. Freiberg, Marienberg, Annaberg, Schneeberg, Johann-Georgenstadt; Joachimsthal; Schenitz and Kremnitz; Königsberg; Huel Duchy, Dolcoath, Herland, and near Callington, in Cornwall; Alva in Stirlingshire. Common ore at Guanaxato and Zacatecas in Mexico, in Peru, and Blagodat in Siberia. Valuable ore of silver.

439. STROMERITE.—Cu + Ag.

Rhombic; isomorphous with redruthite. Crystals rare; usually massive, or in plates; fracture flat, conchoidal, or even; very sectile. \( H = 2\frac{1}{2}...3 \); \( G = 6\frac{1}{2}...6\frac{3}{4} \). Bright. Blackish lead-gray. B.B. fuses easily to a gray metallic semimalleable globule. Chem. com. 52-9 silver, 31-4 copper, and 15-7 sulphur, but often indeterminate proportions of silver 3 to 53, and copper 30 to 75. Schlangenberg in Siberia, Rudelstadt in Silesia, and Catemo in Chili. Ore of silver and copper.

*440. REDRUTHITE.—Cu.

Rhombic; \( \alpha P (a) 119°35', P (P) middle-edge 125°22', \frac{1}{2} P (a) middle-edge 65°40', 2 P \approx (d) middle-edge 125°40', \frac{1}{2} P \approx (e) middle-edge 65°48'. Crystals OP -\( \approx \) \( \approx P (o) \approx P (p), (fig. 245). Mostly thick tabular; also macles; and massive, in plates or lumps. Cleavage, \( \approx P \) imperfect; fracture conchoidal or uneven; very sectile. \( H = 2\frac{1}{2}...3 \); \( G = 5\frac{1}{2}...5\frac{3}{4} \). Rather dull; brighter on the streak. Blackish lead-gray, with a blue or other tarnish. B.B. colours the flame blue; on charcoal in the ox. flame spatters and fuses easily; in the red. flame becomes solid. With soda gives a grain of copper. Green solution in nitric acid. Chem. com. 79-8 copper, and 20-2 sulphur. Saxony, Sile- sia, Norway, the Bannat, Siberia, and the United States; near Redruth and Land's End in Cornwall; Fassnet Burn in Haddingtonshire, in Ayrshire, and in Fair Island, Orkney. Important copper ore.

Digenite.—Massive. \( G = 4\frac{5}{6}...4\frac{6}{8} \); in other respects like redruthite. Contains 70-20 copper, 29-56 sul- phur, and 0-24 silver. Sangerhausen in Thuringia, and Chili.

441. KUPFERINDIG.—Covellite.—Cu.

Hexagonal. Crystals \( \approx P \). OP rare; usually reniform, and fine granular. Cleavage, basal often very perfect; sectile, and thin laminae flexible. \( H = 1\frac{1}{2}...2 \); \( G = 3\frac{1}{2}...3\frac{3}{4} \). Dull resinous, inclining to metallic. Indigo-blue, inclining to black; streak black. B.B. burns with a blue flame; on charcoal like redruthite, but remains fluid in the inner flame; soluble in nitric acid. Chem. com. 66-7 copper, and 33-3 sulphur. Vesuvius, Sangerhausen, Baden-weiler, Schwarzwald; Kielce in Poland, Leogang in Salz-burg, and Cairn Beg in Cornwall.

442. EUKALBIT.—Cu + Se + Ag Se.

Massive and fine granular. Soft (cuts with the knife). Lead-gray; streak shining. B.B. fuses to a brittle gray metallic grain. Chem. com. 43 silver, 25-2 copper, and 31-8 selenium. Skricketum in Smoland.

443. BERZELINE.—Cu + Se.

Crystalline, in thin dendritic crusts. Soft. Silver-white; streak shining. B.B. on charcoal fuses to a gray, slightly malleable bead. With soda a grain of copper. Chem. com. 61-5 copper and 38-5 selenium. Skricketum in Sweden, Lerbach in the Harz.

444. NAGYAGITE.—Black or Foliated Tellurium.

Tetragonal; \( P 137°52', P \approx 122°50', \text{and } OP \). Crys-tals tabular, but rare; in general thin plates or foliated. Cleavage, basal very perfect; very sectile; the thin laminae flexible. \( H = 1...1\frac{1}{2} \); \( G = 6\frac{5}{8}...7\frac{1}{2} \). Splendid. Blackish lead-gray. B.B. fuses easily, with white fumes, and forms a yellow deposit on the charcoal; with soda leaves a grain of gold; soluble in nitric acid, with residue of gold. Chem. com. 51 to 63 lead, 6-7 to 9 gold, 1 to 1-3 copper and silver, 13 to 32 tellurium, 3 to 12 sulphur, and 0 to 4-5 antimony. Nagyag in Siebenburg, and Offenbanya.

445. ALTAYITE.—Pb Te.

Tesseral and granular; hexahedral cleavage. Fracture uneven; sectile. \( H = 3...3\frac{1}{2} \); \( G = 8\frac{1}{2}...8\frac{3}{4} \). Tin-white inclining to yellow, with yellow tarnish. B.B. on charcoal colours the flame blue; in the red. flame fuses to a globule that almost wholly volatilizes. Chem. com. 61-9 lead with 1-28 silver, and 38-1 tellurium. Sawodinski mine in the Altai.

446. HESSEITE.—Ag Te.

Massive and granular; slightly malleable. \( H = 2\frac{1}{2}...3 \); \( G = 8\frac{3}{4}...8\frac{3}{4} \). Blackish lead gray to steel-gray. B.B. on charcoal fumes, fuses to a black grain with white spots, and leaves a brittle grain of silver. Chem. com. 62-8 silver, and 37-2 tellurium, but some (Patzite) 0-7...18 gold. Sawodinski mine in the Altai, Nagyag in Siebenburg.

447. TETRADYMITE.—Bi Te + Bi S.

Rhombohedric; \( 3 R 66°40' \). Crystals \( 3 R \), OR; almost always macles, with the faces of OR at 95°; also granular foliated. Cleavage, basal very perfect; sectile, and in thin laminae flexible. \( H = 1...1\frac{1}{2} \); \( G = 7\frac{1}{2}...7\frac{3}{4} \). Dull. Tin-white to steel-gray. B.B. on charcoal fuses easily, occasionally with odour of selenium, staining the support yellow and white; at length yields a white grain of metal, almost entirely volatile; soluble in nitric acid. Chem. com. 59-66 bismuth, 35-86 tellurium, and 4-48 sulphur, with traces of selenium; but the tellurium and bismuth are isomorphous, and probably in indeterminate proportions, the sulphur and selenium not essential. Schubkau near Schenitz, Deutsch-Pilsen in Hungary, San Jose in Brazil, Virginia and Caro-lina.

*448. MOLYBDENITE.—Mo.

Hexagonal; but only tabular or short prismatic crystals of OP, \( \approx P \) or OP. P. Generally scaly or curved foliated. Cleavage, basal very perfect; very sectile, and thin laminae flexible. Feels greasy. \( H = 1...1\frac{1}{2} \); \( G = 4\frac{1}{2}...4\frac{3}{4} \). Reddish lead-gray; makes a gray mark on paper, a greenish mark on porcelain. B.B. in the forceps colours the flame siskin-green, but is infusible. On charcoal yields sulphurous fumes, and forms a white coating, but burns slowly and imperfectly. In warm nitrochloric acid forms a greenish, in boiling sulphuric acid a blue solution. Chem. com. 59 molybdena and 41 sulphur. Arendal, Altenberg, Ehrenfriedersdorf, Zinnwald, Schlackenwald, Mont Blanc, Shutesbury in Massachusetts, in Maine, Haddam in Connecti-cut; Caldbeckfell in Cumberland, Shap in Westmore-land, Huel Gorland, and many Cornish mines; Peterhead, Corybuy on Loch Crean, and Glenclg. Readily distin-guished from graphite by its streak, lustre, gravity, and action before the blowpipe. Used for preparing blue car-mine for colouring porcelain.

FAMILY III.—GRAY ANTIMONY ORE.

Crystallization rhombic, rarely tesseral or hexagonal. \( H = 3...3\frac{1}{2} \), or less; \( G = 4...6\frac{3}{4} \) (sylvanite 8 1). Colour steel or lead gray. All soluble in acids with precipitates; generally very easily fusible, even in the flame of a candle, and give out fumes.

449. STIBINE, Antimony—Sb".

Rhombic; P polar edges 109° 16', and 108° 10', ΦP 90° 45'. Crystals Φ (m), ΦP (o), ΦP (P), or with ΦP (a), 2ΦP (b), ΦP (e), ΦP (s) (fig. 246). Mostly long prismatic or acicular, with strong vertical striæ, often in druses, or stellar groups; also radiating, fibrous, or fine granular. Cleavage, brachydiaagonal (o) highly perfect, and often horizontally striated; also basal, ΦP, and macrodiaagonal imperfect; sectile. H. = 2; G. = 6·833. Lead-gray. B.B. decrepitates violently; on charcoal fuses readily, leaving lead and silver. Prizibram.

456. PLUMOSITE, Feather Ore.—Ph³ Sb".

Rhombic (7); acicular or capillary, in felt-like masses. H. = 1...3; G. = 5·7...5·9. Dull or glimmering. Dark-lead or steel-gray, sometimes iridescent. B.B. and with acids acts like zincenite; fuses even in the flame of a candle. Chem. com. 51·8 lead, 29·7 antimony, and 19·5 sulphur. Wolfberg, Andreasberg, and Clausthal; Neudorf in Anhalt, Freiberg, and Schenmizitz.

457. ENARGITE—Cu² + As.

Rhombic; Φ P 97° 53', ΦP 100° 58', mostly massive and granular. Cleavage, ΦP perfect, brachy- and macro-diaagonal less so; brittle. H. = 3; G. = 4·43...4·45. Iron-black. In the closed tube yields first sulphur, then fuses and gives out sulphuretted arsenic. B.B. with borax, gives a bead of copper. Chem. com. 48·3 copper, 19·1 arsenic, and 32·6 sulphur. Morococha in Peru.

458. DUFRENOYSITE—Cu² As⁺ + Cu² As⁺.

Tesseral. Crystals ΦO. 202. Fracture uneven; brittle. H. = 2...3; G. = 4·48. Steel-gray; streak reddish-brown. In the closed tube gives a reddish-brown sublimate. B.B. fuses easily, leaving a grain of copper readily soluble in warm acid. Chem. com. 38·4 copper, 2·8 lead, 1·3 silver, 30·5 arsenic, and 27 sulphur. Binenthal, St Gotthardt.

459. SKLEROLITE—Ph³ As⁺.

Rhombic; ΦP 115° 16', ΦP : ΦP = 134° 59'. Crystals broad prismatic, acicular or fibrous; very brittle and friable. G. = 5·39...5·55. Bright metallic. Pale lead-gray, steel-gray, and iron-black; streak reddish-brown. Chem. com. 57·12 lead, 20·74 arsenic, 22·14 sulphur, with traces of silver, copper, and iron. St Gotthardt, with Dufrenoysite, for which it was analyzed.

460. WOLFSBERGITE—Cu² Sb⁺.

Rhombic; ΦP 136° 12', ΦP 111°. Crystals tabular; also fine granular. Cleavage, brachydiaagonal very perfect, basal imperfect; fracture conchoidal or uneven. H. = 3·5; G. = 4·748. Lead-gray to iron-black, sometimes iridescent; streak black, dull. B.B. decrepitates, fuses easily, and with soda gives a grain of copper. Chem. com. 25·4 copper, 49 antimony, and 25·6 sulphur. Wolfberg in the Harz.

461. BERTHIERITE—Fe³ Sb⁺.

Massive; columnar or fibrous, with indistinct cleavage. H. = 2...3; G. = 4·0...4·3. Dark steel-gray, yellowish or reddish; easily tarnished. B.B. on charcoal fuses easily, with fumes of antimony, to a black magnetic slag; soluble in h. acid. Chem. com. sulphurets of iron and antimony in variable proportions, or 9·8 to 16 iron, 52 to 61·6 antimony, and 29·1 to 31 sulphur. Auvergne and Anglar in France, Braunsdorf in Saxony, Tintagel and Padstow in Cornwall. In France used as an ore of antimony.

462. BISMUTHINE—Bi⁺.

Rhombic; Φ P 91° 30'. Crystals long prismatic or acicular, with strong striæ; also granular or columnar, foliated or radiated. Cleavage, brachydiaagonal perfect, macrodiaagonal less distinct; sectile. H. = 2...2·5; G. = 6·4...6·6. Light lead-gray to tin-white, with a yellowish or iridescent tarnish. B.B. on charcoal fuses easily in the inner flame, spatters, and yields a yellow coating with a grain of bismuth; soluble in nitric acid. Chem. com. 81·2 bismuth and 18·8 sulphur. Riddarhyttan, Bastnæs, Johann-Georgenstadt, Altenberg, Joachimsthal; Haddam in Connecticut; near Redruth, Botallack, Dolcoath, and Herland in Cornwall, and Caldbeckfell in Cumberland. 463. **ACICULITE**, Needle-ore.—$\text{Pb}^2\text{Bi}^+ + \text{Cu}^2\text{Bi}^-$. Rhombic; long thin crystals imbedded in quartz, often bent or broken, with strong vertical striae. Cleavage imperfect; fracture conchoidal or uneven; rather brittle. $H = 2\frac{1}{2}$; $G = 6\frac{7}{8}$. Blackish lead-gray or steel-gray, with a brownish tarnish. B.B. fuses very easily, smokes, stains the charcoal white and yellow, and leaves a metallic globule; soluble in nitric acid. Chem. com. 35-8 lead, 11 copper, 36-7 bismuth, and 16-5 sulphur. Beresof in Siberia.

464. **KOBELLITE**—$3\text{Pb}^2\text{Bi}^+ + \text{Fe}^3\text{Sb}^{2+}$. Radiated columnar; soft. $G = 6\frac{29}{32}$. Blackish lead-gray to steel-gray; streak black. B.B. fuses (at first boiling, then quietly), and stains the charcoal white and yellow, and leaves a white grain of metal; soluble in conc. acid, leaving sulphuretted hydrogen. Chem. com. 46 sulphuret of lead, 33-3 sulphuret of bismuth, 5-7 sulphuret of iron, and 15 sulphuret of antimony. Hvena in Nerike, Sweden.

465. **SILVANITE**—$\text{Ag Te}^1 + \text{Au Te}^1$. Rhombic; crystals generally small, short acicular, and often grouped in rows like letters. Cleavage in two directions, one very perfect; sectile, but friable. $H = 1\frac{1}{2}$; $G = 7\frac{99}{100}$. Steel-gray to tin-white, silver-white, and pale bronze-yellow. B.B. on charcoal forms a white coating, and fuses to a dark-gray globule, with soda reduced to a malleable grain of argentiferous gold; soluble in nitrochloric acid, depositing chloride of silver; and in nitric acid, leaving gold. Chem. com. 59-6 tellurium, with 0-5 to 8-5 antimony, 26-5 gold (in some 30), and 13-9 silver, with 0-2 to 19-5 lead. Offenbanya (Graphic Tellurium), Nagyag (Yellow Tellurium).

**Family IV.—Gray Copper Ore.**

Crystallization rhombic and tesserall. $H = 1\frac{1}{2}$, the ores of copper being above 3, the ores of silver below 3; $G = 4\frac{2}{3}$. Colour steel or lead-gray, in a few inclining to black or brown. All soluble in nitric acid. B.B. fusible, often easily, with fumes of sulphur or arsenic. Mostly sulphurets of copper and silver, with sulphurets of arsenic or antimony.

*466. **FAHLORE**—$(\text{Cu}, \text{Ag}, \text{Fe}, \text{Zn}, \text{Hy})^2(\text{Sb}, \text{As})$. Gray Copper.*

Tesseral and tetrahedral. In crystals $\frac{O}{2} > \frac{O}{2}$, $\frac{\infty O}{2}$. Macles (fig. 245), not uncommon; most abundant massive and disseminated. Cleavage, octahedral imperfect, with traces in other directions; fracture conchoidal, uneven, or fine granular; brittle. $H = 3\frac{1}{2}$; $G = 4\frac{3}{4}$. Steel-gray to iron-black; streak black (dark-red when containing zinc). B.B. on charcoal boils slightly, and fuses to a steel-gray slag, usually magnetic, and with soda gives copper. In nitric acid the powder forms a brownish-green solution. Chem. com. very variable; but 15 to 40 copper, 0 to 31 silver, 1 to 6 iron, 1 to 7 zinc, 0 to 7-5 mercury, 12 to 29 antimony, 0 to 10 arsenic, and 23 to 27 sulphur; those with much arsenic are paler coloured; those with little or no arsenic dark-coloured; those with 17 to 31 silver are the silver faehlore (Freiberg), Harz, Müsen, Freiberg, Camsdorf, Alsace, Kremnitz, Kapnik; Crinnis and other Cornish mines near St Austell; Airthrie near Stirling, and Sandlodge in Zetland. Ore of copper and silver.

467. **TENNANTITE**—$(\text{Cu}, \text{Fe})\text{As}^2$. Tesseral; like faehlore. Cleavage, $\infty O$ very imperfect; brittle. $H = 4$; $G = 4\frac{3}{4}$. Blackish lead-gray to iron-black; streak dark reddish-gray. B.B. decrepitates, burns with a bluish flame and odour of arsenic, and fuses to a magnetic slag. Chem. com. 49 copper, 4 iron, 19 arsenic, and 28 sulphur. Redruth and St Day, Cornwall, and Skutterud. Copperblende, with brownish-red streak; $G$, $= 4\frac{3}{4}$; contains 89% zinc; Freiberg.

468. **BOURNONITE**—$\text{Pb}^2\text{Sb}^2 + \text{Cu}^2\text{Sb}^2$. Rhombic; $\infty P(d) 93° 40'$, $\infty P(e) 96° 13'$, $\infty P(x) 92° 34'$, $\infty P(r)$, $\infty P(x)$, $\infty P(x)$, (k), as in fig. 249. Crystals generally thick tabular, very often macked by a face of $\infty P$, and several times repeated; also granular or disseminated. Cleavage, brachydagonal imperfect, traces in other directions; fracture uneven to conchoidal; rather brittle. $H = 2\frac{1}{2}$; $G = 5\frac{7}{8}$. Lustre brilliant metallic. Steel-gray, inclining to lead-gray and iron-black. B.B. usually decrepitates and fuses easily to a black globule, staining the charcoal first white, then yellow, and with soda leaves a grain of copper. In nitric acid a blue solution. Chem. com. 41-8 lead, 12-9 copper, 26 antimony, and 19-3 sulphur. Harz (Neendorf), Braunsdorf, Kapnik, Servoz, Alais and Pontigbaud, Redruth and Beechaston.

469. **WÖLCHITE**—$\text{Cu}^2\text{Sb}^2 + \text{Pb}^2\text{As}^2$. Rhombic; in short prisms. Cleavage, brachydagonal rather distinct; fracture imperfect conchoidal; brittle. $H = 3$; $G = 5\frac{7}{8}$. Blackish lead-gray. B.B. on charcoal fuses with effervescence to a lead-gray metallic grain. Chem. com. 29-90 lead, 17-35 copper, 1-40 iron, 16-65 antimony, 6-04 arsenic, and 28-60 sulphur. Wölch, near St Gertraud, Carinthia.

470. **FREISELEBENITE**—$\text{Ag}^2\text{Sb}^2 + \text{Pb}^2\text{Sb}^2$. Monoclinobedric; $C = 87° 46'$; $\infty P 119° 12'$, $\infty P 131° 41'$, in prisms with curved reed-like faces and strong vertical striae. Macles intersecting; also massive. Cleavage, $\infty P$ perfect; fracture conchoidal or uneven; rather brittle. $H = 2\frac{1}{2}$; $G = 6\frac{2}{3}$. Steel-gray to dark lead-gray; streak the same. B.B. on charcoal fuses to a grain of silver. Chem. com. 22-5 silver, 32-4 lead with copper, 26-8 antimony, and 18-3 sulphur. Rare. Freiberg in Saxony; also Kapnik and Ratiborschitz (?).

471. **STEPHANITE**—$\text{Ag}^2\text{Sb}^2$. Rhombic; $\infty P(o) 115° 39'$, $P(P)$ middle edge 104° 20', $2\infty P(d)$ middle edge 107° 48', $0\infty P(s)$, $\infty P(x)(p)$ (fig. 250), thick tabular or short prismatic, Macles frequent, repeated three or four times; also massive. Cleavage ($d$ and $p$), both imperfect; fracture conchoidal or uneven; sectile. $H = 2\frac{1}{2}$; $G = 6\frac{2}{3}$. Iron-black to blackish lead-gray, rarely iridescent. B.B. on charcoal (odour of arsenic) fuses to a dark-gray globule; with soda, a grain of silver. Chem.com. 70-9 silver, 13-5 antimony, and 15-6 sulphur, but with 0 to 5 iron, or 0-5 to 4 copper, and 0 to 3-3 arsenic. Freiberg, Schneeberg, Johann-Georgenstadt, and Annaberg; Joachimsthal and Przibram, Schemnitz, the Harz, Mexico, Peru, Siberia, and Cornwall. Valuable ore of silver.

472. Polybasite.—(Ag', Cu') (Sb", As").

Hexagonal; P 117°. Crystals OP, αP and OP, P, tabular, and often very thin; also massive. Cleavage, basal imperfect; sectile, and easily frangible. H. = 2...2.5; G. = 6.0...6.25. Iron-black. B.B. decrepitates slightly and fuses very easily. Chem. com. 64 to 72 silver, 3 to 10 copper, 16 to 17 sulphur, 0.2 to 8 antimony, and 1 to 6 arsenic. Freiberg, Joachimsthal, Schenmizitz, and Guanaxuato. An ore of silver.

473. Sternbergite.—Ag' + 2 Fe" (t).

Rhombic; P middle edge 118°, section (or αP) 119° 30'. Crystals usually thin tabular, in macles or in fan-like and spheroidal groups. Cleavage, basal very perfect; sectile, and flexible in thin laminae. H. = 1...1.5; G. = 4.2...4.25. Dark pinchbeck-brown, often a violet-blue tarnish; streak black. B.B. on charcoal fuses to a magnetic globule covered with silver, with borax, a grain of silver; decomposed by nitrochloric acid. Zinne found 33.2 silver, 36 iron, and 30 sulphur; or nearly 1 atom silver, 4 iron, and 6 sulphur. Joachimsthal, Schneeberg and Johann-Georgenstadt.

Flexible Sulphuret of Silver is identical; Hungary and Freiberg.

474. Stannine, Tin Pyrites.—Cu' Sn' + (Fe', Zn') Sn'.

Tesseral; in cubes very rare, generally massive and granular. Cleavage, hexahedral very imperfect; fracture uneven or small conchoidal; brittle. H. = 4; G. = 4.3...4.5. Steel-gray (yellowish from copper pyrites); streak black. B.B. on charcoal fuses, forming round the assay a white coating; with soda, a grain of copper; easily decomposed by nitric acid, leaving tin peroxide and sulphur; the solution is blue. Chem. com. 26 to 32 tin, 24 to 30 copper, 5 to 12 iron, 2 to 10 zinc, and 30 sulphur. Huel Rock near St Agnes, St Michael's Mount, and Carn Brea, Cornwall; and Zinnwald. Bell-metal ore.

475. Wittichenite, Cuprous Bismuth.—Cu' Bi".

Rhombic (?); massive. Cleavage, vertical distinct; fracture uneven and fine granular; sectile. H. = 3.5; G. = 5. Steel-gray, pale lead-gray tarnish; streak black. B.B. fuses very readily, frothes, and stains the charcoal yellow; with soda, a grain of copper. Chem. com. 38.5 copper, 42 bismuth, and 19.5 sulphur. Wittichen in Schwarzwald, Huel Buller in Cornwall.

476. Bismuthic Silver.

Acicular, capillary, or massive; sectile and soft. Pale lead-gray, darker tarnish. B.B. fuses easily, and forms a large deposit on the charcoal. Klaproth found 33 lead, 27 bismuth, 15 silver, 4.3 iron, 0.9 copper, and 16.3 sulphur. Schapbach Valley in Baden.

Family V.—Blendes.

Crystallization mostly tesseral; cleavage distinct. H. = 3.5...4.5; G. = 3.5...4.9. Lustre adamantine or resinous; more or less translucent. Colours and streak red, yellow, brown, or black. All soluble in acids. B.B. often decrepitate, but fuse with difficulty.

*477. Blende, Zinc-blende.—Zn'.

Tesseral and tetrahedral; O = O (sometimes as O), αO, 303°/2 and αOα. Macles remarkably common, united by a face of O (fig. 251) and several times repeated; frequently massive and granular. Cleavage, αO very perfect; very brittle. H. = 3.5...4; G. = 3.9...4.2. Semitransparent to opaque; adamantine and resinous. Brown or black, also red, yellow, and green. B.B. decrepitates often violently, but only fuses on very thin edges; soluble in conc. nitric acid, leaving sulphur. Chem. com. 66.8 zinc and 33.2 sulphur, but generally with 1 to 15 iron, 0 to 3 cadmium. Very abundant, the Harz, Freiberg, Piribram, Schenmizitz, Kapnik, North America, Peru, Cornwall, Derbyshire, Cumberland, Leadhills, and Stotfield, near Elgin. Used as an ore of zinc, but with little success.

478. Voltzine.—4 Zn' + Zn.

Hemispherical, curved-lamellar incrustations. Fracture conchoidal. H. = 4.5; G. = 3.66. Brick-red to yellow or brown. Opaque or semitranslucent; vitreo-resinous; pearly. B.B. like zinc-blende; soluble in h. acid. Chem. com. 82.8 sulphuret and 17.2 oxide of zinc. Pontgibaud in Auvergne, and Joachimsthal.

479. Alabandine.—Mn'.

Tesseral; O and αOz; usually massive and granular. Cleavage, hexahedral perfect; fracture uneven; rather brittle. H. = 3.5...4; G. = 3.9...4. Opaque; semimetallic. Iron-black to dark steel-gray, brownish-black tarnish; streak dark green. B.B. fuses on thin edges to a brown slag; soluble in h. acid. Chem. com. 63.6 manganese and 36.4 sulphur. Nagyag and Kapnik, Mexico and Brazil.

480. Haueite.—Mn'.

Tesseral; O, αOz, and αO. Crystals single or in spherical groups. Cleavage, hexahedral perfect. H. = 4; G. = 3.463. Semitranslucent on very thin edges; metallic-adamantine. Reddish-brown to brownish-black; streak brownish-red. In the closed tube yields sulphur, and leaves a green mass, which B.B. becomes brown on the surface, and is soluble in h. acid. Chem. com. 46.28 manganese and 53.72 sulphur. Kalinka, near Neusohl in Hungary.

481. Greenockite.—Cd'.

Hexagonal and hemihedral; P 87° 13', 2P 124° 34'. Crystals 2P, OP, αP, P, or P, 2P, αP; attached singly. Cleavage, αP imperfect, basal perfect. H. = 3...3.5; G. = 4.8...4.9. Translucent; brilliant resinous, or adamantine. Honey or orange-yellow, rarely brown; streak yellow. B.B. decrepitates and becomes carmine-red, but again yellow when cold; fused with soda forms a reddish-brown coating on charcoal; soluble in h. acid. Chem. com. 77.6 cadmium, and 22.4 sulphur. Bishoptown in Renfrewshire.

Family VI.—Ruby-Blendes.

Crystallization rhombohedric, monoclinohedric, or rhombic. Cleavage rarely distinct. H. = 1.5...2.5; G. = 3.5...8.2. Lustre adamantine. Colour yellow, red or gray; streak deep red, rarely brownish or yellow. Soluble in nitric acid. B.B. fusible and reduced often with fumes, or sublime.

*482. Pyrargyrite, Red Silver.—Ag' Sb".

Rhombohedric; R (P) 108° 42', -R 137° 58', OR. -2R (r), R', αP2 (s), and αR (t). Crystals prismatic (figs. 252, 253); macles common of various kinds; also massive, dendritic, or investing. Cleavage, R rather perfect; fracture conchoidal to uneven and splintery; slightly sectile, sometimes almost brittle. H. = 2...2.5; G. = 5.75...5.85. Translucent on the edges to opaque; crimson-red to blackish lead-gray; streak cochineal to cherry-red. B.B. on charcoal

Miara- logy.

fuses easily, gives out sulphurous acid and antimony fumes, and leaves a grain of silver; soluble in nitric acid, leaving sulphur and antimony protoxide; solution of potash extracts sulphuret of antimony. Chem. com. 59°8 silver, 22°3 antimony and 17°7 sulphur. Andreasberg, Freiberg, Johann-Georgenstadt, Annaberg, Schneeberg, and Marienberg; Przibram, Schenmitz and Kremnitz, Markirchen, Kongsberg and Mexico; Huel Brothers and Huel Duchy in Cornwall.

483. PROUSTITE.—AgI AsI.

Rhombohedric, like pyrargyrite, except R, 107°50'. G. 5°5...5°6. Semitransparent to translucent on the edges. Cochineal to crimson red; streak aurora-red to cochineal-red. B.B. arsenical odour, and leaves a brittle metallic grain difficultly reduced to pure silver; soluble in nitric acid, with remainder of sulphur and arsenious acid; solution of potash extracts sulphuret of arsenic. Chem. com. 65°4 silver, 15°1 arsenic, and 19°4 sulphur. In the same localities with pyrargyrite, and both valuable ores of silver. Red orpiment has a lower specific gravity and yellow streak; cinnamon bar volatilizes before the blowpipe.

484. MIAOGEYRITE.—AgI SbI.

Monoclinohedric; C = 81°36', P = 90°53', -P = 95°59'. Crystals pyramidal, short prismatic, or tabular (fig. 254); also massive. Cleavage, indistinct traces; fracture imperfect conchoidal or uneven; sectile. H. = 2...2°5; G. = 5°3...4°. Opaque; thin splinters dark blood-red, translucent; metallic adamantine. Blackish lead-gray to iron-black and steel-gray; streak cherry-red. B.B. with soda, a grain of silver; with acids, like pyrargyrite. Chem. com. 35°9 silver, 42°9 antimony, and 21°2 sulphur. Bräunsdorf near Freiberg.

Rittingerite.—Monoclinohedric; C = 88°26', -P = 126°18'. Crystals small tabular. Cleavage basal imperfect; brittle. H. = 2°5...3°. Translucent honey-yellow to red. Colour iron-black, on OP brown tarnished; streak orange-yellow. B.B. melts easily, with arsenic fumes, leaving much silver. Joachimsthal.

485. XANTHOKON.—AgI AsI + AgI AsI.

Rhombohedric. Crystals very thin hexagonal tables, with R: OR 110°30', -2R: OR 100°35'. Cleavage, R and OR more or less perfect; rather brittle, very easily frangible. H. = 2...2°5; G. = 5°0...5°2. Translucent and transparent; adamantine. Orange-yellow or yellowish-brown; streak slightly darker. In the closed tube fuses very easily, becomes lead-gray. Chem. com. 63°4 silver, 14°7 arsenic, and 21°9 sulphur. Himmlsfürst Mine at Freiberg.

Fireblende.—In thin tabular crystals (like hemantite), with one perfect cleavage; sectile and slightly flexible. G. = 4°2...4°3. Hyacinth-red. B.B. like pyrargyrite. Contains sulphur, antimony, and silver. Freiberg and Andreasberg.

486. KERME.—SbI + Sb.

Monoclinohedric (?). Crystals acicular, capillary, and diverging; also radiating fibrous. Cleavage, very perfect along the axis of the crystals, less perfect at right angles; sectile. H. = 1...1°5; G. = 4°5...4°6. Semitranslucent; adamantine. Cherry-red; streak similar. B.B. acts like stibine; soluble in h. acid; in solution of potash the powder becomes yellow and dissolves. Chem. com. 75°3 antimony, 19°8 sulphur, and 4°9 oxygen; or 70 sulphuret and 30 protoxide of antimony. Bräunsdorf near Freiberg, Przibram, and Allemont.

Zundererz, or Tinder-ore, soft, flexible, tinder-like masses, dirty cherry-red or blackish-red, is a mixture; Andreasberg.

487. CINNABAR.—HgI.

Rhombohedric; R 71°48', OR 4°R, 3°R, -OR. Crystals rhombohedric or thick tabular; also disseminated and granular, compact, or earthy. Cleavage, OR rather perfect; fracture uneven and splintery; sectile. H. = 2...2°5; G. = 8...8°2. Semitransparent or opaque; adamantine. Cochinchal-red, with lead-gray and scarlet-red tarnish; Minera- logy. streak scarlet-red. In the open tube sublimes, partly as cinna- har, partly as metallic mercury; perfectly soluble in nitrochloric acid, but not in hydrochloric acid, nitric acid, or solution of potash. Chem. com. 86°2 mercury and 13°8 sulphur. Idria in Carniola, Almaden and Almadenejos in Spain, Wolfstein and Moschellandsberg in Rhenish Bavaria, Hartenstein in Saxony, Szlana and Rosenau in Hungary, Ripa in Tuscany; New Almaden in California, Mexico, and Peru. Principal ore of mercury; also used as a pigment. Fibrous and Hepatic Orpiment are mixtures.

488. REALGAR, Red Orpiment.—AsI.

Monoclinohedric; C = 66°5 (P), -P (M) 74°26', (P) (a) 132°2', -P2 (l) 113°16'. Crystals prismatic (fig. 255); also massive and investing. Cleavage, basal and clinodagonal rather perfect, prismatic imperfect; fracture small conchoidal to uneven or splintery; sectile. H. = 1°5...2; G. = 3°4...3°6. Semitransparent or opaque; resinous. Aurora-red; streak orange-yellow. In the closed tube sublimes as a dark-yellow or red mass; B.B. on charcoal fuses and burns with a yellowish-white flame; acids act on it with difficulty. Chem. com. 70 arsenic and 30 sulphur. Kapnik, Nagrag, Felsobanya, and Tajowa, Andreasberg, St Gotthardt, Vesuvius and the Solfatara.

489. DIMORPHINE.—AsI.

Rhombic, in two types; more common short prismatic, with -P 96°34' and P = 103°50'; the other more pyramidal. Very fragile. H. = 1°5; G. = 3°58. Splendid adamantine; translucent or transparent. Orange-yellow; streak similar. Chem. com. 75°5 arsenic, and 24°5 sulphur. Solfatara, Naples.

490. ORPIMENT.—AsI.

Rhombic; -P 117°49', P = 88°37'. Crystals short prismatic (fig. 256), disseminated, columnar or foliated. Cleavage, brachydagonal very perfect, striated vertically; sectile, and in thin laminae flexible. H. = 1°5...2; G. = 3°4...3°5. Semi-transparent or opaque; resinous or pearly. Citron-yellow to orange-yellow. In the closed tube yields a dark-yellow or red sublimate; fused with soda it yields metallic arsenic; soluble in nitrochloric acid, in potash, and in ammonia. Chem. com. 61 arsenic and 39 sulphur. Tajowa near Neusohl, Servia, Wallachia, Natolla, Felsobanya, Kapnik, and Andreasberg; the Solfatara, and Zimapan in Mexico.

ORDER VII.—THE INFLAMMABLES.

Named from the substances all burning before the blowpipe, whereas the former minerals only fused or gave out fumes, and left a residue. Few of them are crystallized, and many rather organic remains or rocks than simple minerals. In chemical composition they are either simple elements, as sulphur and carbon, or mostly formed not on the plan of the mineral kingdom, but of organic nature. Except the diamond, their hardness is low, or less than 2°5; and their specific gravity also 2°2, or under.

FAMILY I.—SULPHUR.

*491. SULPHUR.—S.

Rhombic; P polar edges 106°38', 84°58'; middle edge 143°17'; -P 101°58', OP, -P, P = . Crystals pyramidal (fig. 257), single or in druses; also reniform, spherical, stalactitic, disseminated, incrusting, or pulverulent. Cleavage, basal and -P imperfect; fracture conchoidal to uneven or splintery; rather brittle. H. = 1°5 Transparent or translucent on the edges; resinous or adamantine. Sulphur-yellow, passing into brown and red, or into yellowish-gray and white. In the closed tube it sublimes; at 227° Fahr. fuses, and at 518° takes fire and burns with a blue flame, forming sulphurous acid. Chem. com. sulphur, occasionally more or less mixed with other substances. Sicily, at Girgenti, Cataldo, &c.; the Lipari Islands, the Solfatara near Naples, Poland, Iceland, Java, Sandwich Islands, Peru, and Chili; from springs at Aix-la-Chapelle, and in Scotland.

492. SELEN-SULPHUR.

Orange-yellow or yellowish-brown. Fuses readily in the closed tube, and volatilizes. B.B. on charcoal burns, and gives out fumes of selenic and sulphurous acids. Consists of sulphur and selenium. Vulcano, Lipari, and Kilauea in Hawaii.

Notice Selenium.—Brownish-black or lead-gray. Thin splinters red translucent. H. = 2; G. = 4-3. Culebras in Mexico.

FAMILY II.—DIAMOND.

493. DIAMOND.—C.

Tesseral and tetrahedral-semitesseral; $\frac{O}{2}$ and $-\frac{O}{2}$, mostly conjoined, $\infty O$, $\infty Om$, $mO$, $mOn$; or the octahedron, rhombic dodecahedron, and hexakisoctahedron (figs. 2, 3, 7, and 5). The crystals have often curved faces, and occur loose or imbedded singly. Maches common, united by a plane of O, like fig. 251. Cleavage, octahedral perfect; fracture conchoidal; brittle. H. = 10; G. = 3-5...36. Transparent or translucent when dark-coloured. Refracts light strongly; brilliant adamantine. Colourless, but often white, gray, or brown tints, also green, yellow, red, blue, and rarely black. Becomes positive electric by friction; burns in oxygen gas, and forms carbonic acid. Chem. com. pure carbon. Hindostan on the east of the Deccan, between Penjar, Sonar, and the delta of the Ganges (lat. 14° to 25°); Borneo and Malacca; Brazil in the district of Serro do Frio in Minas Geraes; also in Borneo, Malacca, the Ural, Georgia, and North Carolina, and the Sierra Madre, south-west from Mexico.

FAMILY III.—The Coals.

494. GRAPHITE.—Plumbago.—C.

Hexagonal or monoclinohedric; but only thin tabular or short prismatic crystals of $0P$. $\infty P$. Usually foliated, radiating, scaly, or compact. Cleavage, basal perfect; very sectile, flexible in thin laminae. Feels greasy. H. = 0-5...1; G. = 1-9...2-2. Opaque; metallic. Iron-black. Leaves a mark on paper. Is a perfect conductor of electricity. B.B. burns with much difficulty; and heated with nitre in a platina spoon only partially detonates. Chem. com. carbon, but mixed with iron, lime, alumina or other matter. Pragas, Arendal, Passau, Spain, Ticonderoga in New York, Ceylon, Borrowdale in Cumberland, Glenstrathfarrer in Inverness-shire, Kirkcudbright, and Craigman in Ayrshire. At the latter it is evidently common coal altered by contact with trap. Is used for making pencils, and to form crucibles.

*495. ANTHRACITE.—Glance-Coal.

Massive and disseminated; rarely columnar, or fibrous and pulverulent. Fracture conchoidal; brittle. H. = 2...2-5; G. = 1-4...1-7. Opaque; brilliant metallic. Iron-black or grayish-black; streak unaltered. Perfect conductor of electricity. Burns difficulty with a very weak or no flame, and does not cake; in the closed tube yields a little moisture, but no empyreumatic oil; detonates with nitre. Chem. com. carbon above 90 per cent., with 1 to 3 oxygen, 1 to 4 hydrogen, and 0 to 3 nitrogen; and ashes chiefly of silica, alumina, lime, and peroxide of iron. Very common in some parts of the English, Scottish, and Irish coal-fields; in the Alps, as the Valais, Piedmont, Savoy, and Dauphine; in the Pyrenees, and in various parts of France; in Silesia, Bohemia, Saxony, and the Harz; and in the United States, as in Rhode Island, Massachusetts, and above all in Pennsylvania. Used for manufacturing metals, and for economic and household purposes.

496. COMMON COAL, Black, Stone, Bituminous Coal.

Compact, slaty, or confusedly fibrous; often dividing into columnar, cubical, or rhomboidal fragments. Fracture conchoidal, uneven, or fibrous; rather brittle or sectile. H. = 2...2-5; G. = 1-2...1-5. Vitreous, resinous, or silky in the fibrous variety. Blackish-brown, pitch-black, or velvet-black. Burns easily, emitting flame and smoke, with a bituminous odour; heated in the closed tube with powdered sulphur gives out sulphuretted hydrogen. Chem. com. 74 to 90 carbon, with 0-6 to 8 or 15 oxygen, 3 to 6 hydrogen, 0-1 to 2 nitrogen, 0-1 to 3 sulphur, and 1 to 11 earthy matters or ash, in 100 parts.

Slate-coal has a thick slaty structure, and an uneven fracture in the cross direction. Camel coal, a resinous, glimmering lustre, and a large or flat conchoidal fracture; breaks into irregular cubical fragments, but more solid, and takes a higher polish than the other varieties. It burns with a bright flame, and yields much gas. Coarse or foliated coal, massive or lamellar, breaks into cubical or irregular angular masses, with a more splendid lustre, and less compact texture than the former, and more easily frangible. Earthly coal, loose powdery masses, often brown or dirty in colour, and apparently semi-decomposed. Abundant in many lands, as in England, South Wales, Scotland, and Ireland; in Belgium and France, in Germany and Southern Russia. The United States possess immense fields in the valley of the Mississippi. Also found in China, Japan, Hindostan, Australia, Borneo, and several of the Indian Islands. Its uses are too well known to need notice.

497. BROWN COAL.—Lignite, Jet.

Distinctly vegetable in origin, the external form, and very often the internal woody structure, being preserved. The texture is compact, woody, or earthy. Fracture conchoidal, woody, or uneven; soft and often friable. G. = 0-5...1-5. Lustre sometimes resinous, mostly glimmering or dull. Brown, black, or rarely gray. Burns easily with an unpleasant odour; colours solution of potash deep-brown; heated with sulphur evolves much sulphuretted hydrogen. Chem. com. 47 to 78 carbon, 2-5 to 7-5 hydrogen, 8 to 33 oxygen (with nitrogen), and 1 to 15 ashes. Jet is pitch-black, with conchoidal fracture and resinous lustre. Brown coal occurs at Bevery Tracey in Devonshire, in Yorkshire, Antrim, Brora, Mull, and Skye; Germany, Hungary, France, Italy, and Greece. The Surturbrand of Iceland seems a variety. Used as fuel, but much inferior to common coal.

*498. PEAT.

A mass of more or less decomposed vegetable matter of a brown or black colour, closely connected with coal, and, like it, rather a rock than a simple mineral. Contains 50 to 60 carbon, 5 to 6 hydrogen, 30 to 39 oxygen, 0 to 2 nitrogen, and 1 to 14 ashes in 100 parts. Common everywhere in the colder parts of the earth.

FAMILY IV.—The Mineral Resins.

*499. BITUMEN, Naphtha.—CH₂.

Liquid. Colourless, yellow, or brown; transparent or translucent. G. = 0-7...0-9. Volatilizes in the atmosphere with an aromatic bituminous odour. Chem. com. 84 to 88 carbon, and 12 to 16 hydrogen.

Naphtha.—Very fluid, transparent, and light-yellow. Tegern Lake in Bavaria, Amiano near Parma, Salices in the Pyrenees, Rangun in Hindostan, Baku on the Caspian Sea, China, Persia, and North America. Used for burning and preparing varnishes.

**Petroleum.** Darker yellow or blackish-brown; less fluid or volatile. Ormskirk in Lancashire, at Coalbrookdale, Pitchford, and Madeley in Shropshire; St Catherine's Well, south of Edinburgh; Isle of Pomona; and in many other parts of Europe and the United States.

*500. Elaterite, Elastic Bitumen.*

Mineral Caoutchouc.

Compact; reniform or fungoid; elastic and flexible like caoutchouc; very soft. G. = 0·8...1·23. Resinous. Blackish, reddish, or yellowish brown. Strong bituminous odour. Chem. com. 84 to 86 carbon, 12 to 14 hydrogen, and a little oxygen. Derbyshire, Montréalais near Nantes, and Woodbury in Connecticut.

501. Asphaltum.

Compact and disseminated. Fracture conchoidal, sometimes vesicular; sectile. H. = 2; G. = 1·1...1·2. Opaque, resinous, and pitch-black; strong bituminous odour, especially when rubbed. Takes fire easily, and burns with a bright flame and thick smoke; soluble in ether, except a small remainder, which is dissolved in oil of turpentine. Chem. com. 76 to 88 carbon, 2 to 10 oxygen, 6 to 10 hydrogen, and 1 to 3 nitrogen. Limmer near Hanover, Seyssel on the Rhone; Val Travers in Neufchatel, Lobsann in Alsace, in the Harz; Cornwall, Haughmond Hill, Shropshire; East Lothian, Burriston in Fifeshire; Dead Sea, Persia, and Trinidad.

502. Piauzite.

Massive; imperfect conchoidal; sectile. H. = 1·5; G. = 1·22. Dimly translucent on very thin edges; resinous. Blackish-brown; streak yellowish-brown. Fuses at 600° Fahr., and burns with an aromatic odour, lively flame, and dense smoke; soluble in ether and caustic potash. Piauzie in Carniola.

503. Ixolite.

Massive; conchoidal fracture. H. = 1; G. = 1·008. Resinous. Hyacinth-red; streak ochre-yellow. Rubbed between the fingers it emits an aromatic odour, and becomes soft at 119°, but is still viscid at 212°. Oberhart near Gloggnitz in Austria.

*504. Amber, Succinite.—C₁₉H₁₀O.*

Round irregular lumps, grains, or drops. Fracture perfect conchoidal; slightly brittle. H. = 2...2·5; G. = 1...1·1. Transparent to translucent or almost opaque; resinous. Honey-yellow, but from hyacinth-red or brown to yellowish-white; also streaked or spotted. When rubbed emits an agreeable odour, and becomes negatively electric. It melts at 550°, emitting water, an empyreumatic oil, and succinic acid; it burns with a bright flame and pleasant odour, leaving a carbonaceous remainder; only a small part is soluble in alcohol. Chem. com. 79 carbon, 10·5 hydrogen, and 10·5 oxygen. Derived from an extinct coniferous tree, and found in the diluvial formations of many countries, especially Northern Germany and shores of the Baltic, Sicily, Spain, and Northern Italy; rarely in England, as on the shores of Norfolk, Suffolk, and Essex; and at Kensington near London. Used for ornamental purposes, and for preparing succinic acid and varnishes.

505. Retinite, Retinaphalt.

Roundish or irregular lumps. Fracture uneven or conchoidal; very easily frangible. H. = 1·5...2; G. = 1·05...1·15. Translucent or opaque; resinous or glistening. Yellow or brown. Melts at a low heat, and burns with an aromatic or bituminous odour. Chem. com. in general carbon, hydrogen, and oxygen, in very uncertain amount. Bovey, Halle, Cape Sable, and Osnabrück.

506. Walchowite.—C₁₂H₁₀O.

Rounded pieces, with a conchoidal fracture. H. = 1·5...2; G. = 1·035...1·069. Translucent, resinous. Yellow with brown stripes; and a yellowish-white streak. It fuses at 482°, and burns readily; soluble partially (7·5 per cent.) in ether, and in sulphuric acid forms a dark-brown solution. Chem. com. 80·4 carbon, 10·7 hydrogen, and 8·9 oxygen. Walchow in Moravia.

507. Copaline, Fossil Copal; Highgate Resin.

Irregular fragments. H. = 1·5; G. = 1·046. Translucent resinous, and light-yellow or yellowish-brown. Burns easily with a bright-yellow flame and much smoke; alcohol dissolves very little of it, which is precipitated by water; becomes black in sulphuric acid. Chem. com. 86·54 carbon, 11·63 hydrogen, 2·76 oxygen. Highgate near London. A similar resin from Settling Stones in Northumberland, found in flat drops or crusts on calc-spar, is infusible at 500° Fahr.; G. = 1·16...1·54; and contains 85·13 carbon, 10·85 hydrogen, and 3·26 ashes; or C₁₂H₁₀O.

508. Berengelite.—C₁₀H₁₀O.

Amorphous; conchoidal fracture. Dark-brown, inclining to green; yellow streak. Resinous; unpleasant odour, and bitter taste. Fuses below 212°, and then continues soft at ordinary temperatures; easily soluble in alcohol. Chem. com. 72·40 carbon, 9·28 hydrogen, 18·31 oxygen. St Juan de Berengela in South America.

509. Guyaquillite.—C₁₀H₁₀O.

Amorphous; yielding easily to the knife, and very friable. G. = 1·092. Pale yellow. Slightly resinous. Fluid at 212°, viscid when cold; slightly soluble in water and largely in alcohol, forming a yellow fluid with a bitter taste. Chem. com. 77·01 carbon, 8·18 hydrogen, and 14·80 oxygen. Guyaquil in South America.

Boothitter, from the Irish peat mosses, is similar; melts at 124°, easily soluble in alcohol, and contains 73·70 carbon, 12·50 hydrogen, and 13·72 oxygen.

510. Hartite.—C₁₀H₁₀O.

Spermaceti-like masses. G. = 1·115. White; without taste or smell. Becomes soft at 392°, and at 410° melts to a clear yellow fluid; burns with a bright flame; it is not soluble in water, very little in ether, and less in alcohol. Chem. com. 78·26 carbon, 10·92 hydrogen, 10·82 oxygen. Oberhart in Austria.

511. Middlefontite.—C₁₀H₁₀O+HO.

Round masses or thin layers. Brittle, but easily cut with a knife. G. = 1·6. Resinous. Reddish-brown by reflected, deep-red by transmitted light; streaked, light-brown. It becomes black on exposure to the atmosphere. Chem. com. 86·44 carbon, 8·01 hydrogen, 5·56 oxygen. In the main coal seam at Middleton near Leeds, and at Newcastle.

512. Ozokerite.—CH.

Amorphous, sometimes fibrous. Very soft, pliable, and easily fashioned with the fingers. G. = 0·94...0·97. Glittering or glistening; semitranslucent. Yellowish-brown or hyacinth-red by transmitted, dark leek-green by reflected light. Pleasant aromatic odour; fuses easily (at 144°, Schröter; at 183°, Malagutti) to a clear oily fluid, again becoming solid when cold, and at higher temperatures burns with a clear flame, seldom leaving any ashes; readily soluble in oil of turpentine, with great difficulty in alcohol or ether. Chem. com. 85·7 carbon, and 14·3 hydrogen. Slanik and Zietriska in Moldavia, and near Garning in Austria. Also Urpeth coal mine near Newcastle-on-Tyne.

513. Hatchetine, Mineral Tallow.

Flaky, like spermaceti; or sub-granular, like bees' wax; soft and flexible. G. = 0·6. Translucent; weak pearly. Yellowish-white, wax-yellow, or greenish yellow. Greasy; inodorous; readily soluble in ether. Chem. com. 85·91 carbon, and 14·62 hydrogen, or similar to ozokerite. Glamorganshire (fusible at 115°); Loch Fyne near Inverary. Also Merthyr-Tydfil (melts at 170°), and Sookdorf in Schaumburg. 514. Fichtelite.—C₄ H₄.

Crystalline lamellae, which swim in water, but sink in alcohol. White and pearly. Fuse at 115°, but again become crystalline on cooling; very easily soluble in ether, and precipitated by alcohol. Chem. com. 89-3 carbon and 10-7 hydrogen. In pine trees in a peat moss near Redwitz in Bavaria.

515. Harrite.—C₆ H₄.

Resembles spermaceti or white wax; lamellar, and probably monoclinohedric. Sectile, but not flexible. H.=1; G.=1-046. Translucent; dull resinous. White. Melts at 165°, and burns with much smoke; very soluble in ether, much less so in alcohol. Chem. com. 87-50 carbon, and 12-10 hydrogen. Oberhart in Austria.

516. Könnite.—C₂ H₄.

Crystalline folie and grains. Soft. G.=0-888. Translucent; resinous. White, without smell. Fuses at 120° to 137° Fahr.; soluble in nitric acid, and precipitated by water in a white crystalline mass. Chem. com. 92-31 carbon and 7-69 hydrogen. Uznach near St Gallen, Redwitz in Bavaria.

517. Scheererite.—CH₃.

Monoclinohedric; tabular or acicular. Soft and rather brittle. G.=1-0...1-2. Translucent; resinous or adaman-tine. White, inclining to yellow or green. Feels greasy, has no taste, and when cold no smell, but when heated a weak aromatic odour. Insoluble in water; but readily in alcohol, ether, nitric, and sulphuric acid. Chem. com. 75 carbon, and 25 hydrogen. Uznach. Branchite, white, translucent, feels greasy, and fuses at 167°, is similar; Monte Vaso in Tuscany.

518. Idrialite.—(Idrialine = C₉₈ H₁₄ O).

Massive; fracture uneven or slaty. Sectile. H.=1-0...1-5; G.=1-4...1-6 (1-7...3-2). Opaque; resinous. Grayish or brownish-black; streaked blackish-brown, inclining to red. Feels greasy. Burns with a thick smoky flame, giving out sulphurous acid, and leaving some reddish-brown ashes. Chem. com. idrialine (=91-83 carbon, 5-30 hydro-gen, and 2-87 oxygen) and cinnabar, with a little silica, alumina, pyrite, and lime. The idrialine may be extracted by warm olive oil or oil of turpentine, as a pearly shining mass. Idria.

Family V.—Inflammable Salts.

519. Mellite, Honey Stone.—Al M₂ + 18 H₂.

Tetragonal; P 93° 6'. Crystals, P alone, or with 6P, P₂O₅, and αP₂O₅, usually single; also massive and granular. Cleavage, P very imperfect; fracture conchoidal; rather brittle. H.=2-0...2-5; G.=1-5...1-7. Transparent to translucent; distinct double refraction; resinous or vitreous. Honey-yellow to wax-yellow or reddish; streak whitish. In the closed tube it yields water. B.B. car-bonizes without any sensible odour, at length burns white, and acts like pure alumina; easily soluble in nitric acid or solution of potash. Chem. com. 40-53 mellic acid (M=C₄ O₄), 14-32 alumina, and 45-15 water. Artern in Thuringia, Lauschitz in Bohemia, and Walchow in Moravia.

520. Oxalite, Humboldtine.—2 Fe C₂ + 3 H₂.

Capillary crystals; also botryoidal or in plates, and fine granular, fibrous, or compact. Fracture uneven or earthy; slightly sectile. H.=2; G.=2-15...2-25. Opaque; weak resinous or dull. Ochre or straw yellow. B.B. on charcoal becomes first black then red; easily soluble in acids. Chem. com. 42-7 oxalic acid, 41-4 iron protoxide, and 15-9 water. Kolosovuk near Bilin, Duisburg, and Gross Alme-rode in Hesse.

521. Wheewellite.—Ca C₂ + 7 H₂.

Monoclinohedric; C=72° 41', αP 100° 36'. Cleavage, basal perfect; very brittle. H.=2-5...2-8; G.=1-833. Transparent to opaque; vitreous. Colourless. Chem. com. 49-31 oxalic acid, 38-36 lime, 12-33 water. Hungary (?).

522. Conistonite.—Ca C₂ + 7 H₂.

Rhombic; αP 97° 5'. Slightly sectile. H.=2; G.=2-032. Transparent to translucent; vitreous. Colourless. Soluble without effervescence in n. acid. Chem. com. 28-1 oxalic acid, 21-8 lime, and 50-1 water. Coniston in Cumberland.

Though properly not a simple mineral, the characters of water in its two conditions may be noted here.

*523. Water.—HO.

Fluid and amorphous. G.=1-000 when pure, but sea-water 1-027 and 1-0285 at 62° Fahr. When pure it is without taste or smell, and colourless in small quantities, but in larger masses green or blue. Chem. com. hydrogen-oxide, with 88-9 oxygen and 11-1 hydrogen. Attains its greatest density at 39° 1', boils at 212°, and at 32° Fahr. freezes and changes to

Ice.

Rhombohedric; R. 117° 23' (120°); usually six-sided tables of 0R. αR; also acicular crystals, macked in delicate groups or stars with six rays. Cleavage, probably basal. H.=1-5; G.=0-9268 (Ossann), 0-918 (Brunner at 32° Fahr., and quite pure). Transparent; vitreous. Colourless, but in large masses greenish or bluish. Refracts double.

The water found on the earth is never pure, but contains more or less of various substances—atmospheric air, carbolic acid, nitrogen gas; silica, alumina, and salts (carbonates, sulphates, nitrates, phosphates) of lime, magnesia, soda, potash, protoxides of iron and manganese; or chlorides, and fluorides of the metallic bases; and in the sea and some saline springs also iodine and bro-mine.

(J.N.—L.)

ALPHABETICAL INDEX OF MINERAL SPECIES.

| Aemite | 110 | Anasultite | 86 | Arsenite | 389 | |-----------------|-----|------------------|----|-----------------|-----| | Ascolite | 463 | Andalusite | 149 | Asphalite | 501 | | Aschynite | 357 | Andesine | 5 | Atacanite | 296 | | Agalmatolite | 133 | Anglelite | 304 | Augite | 101 | | Alabandite | 479 | Anhydrite | 215 | Aurichalcite | 283 | | Albite | 4 | Anorthosite | 8 | Autunnite | 157 | | Allanite | 127 | Anthophyllite | 127 | Azurite | 145 | | Alluphane | 125 | Arcanite | 455 | Azurite | 291, 29 | | Alluaudite | 270 | Antigorite | 90 | Barite | 207 | | Alstonite | 210 | Antimony | 369 | Balingitomite | 111 | | Altaita | 445 | Ochre | 374 | Barytes | 207 | | Alum | 225 | Barite | 396 | Barrys-Calcite | 211 | | Alumite | 210 | Apophyllite | 51 | Barthelite | 461 | | Alumogen | 248 | Apophyllite | 51 | Berthierite | 461 | | Amalgam | 398 | Argentite | 438 | Berzelinite | 222 | | Amber | 504 | Arragonite | 191 | Bessertite | 235 | | Amblygonite | 34 | Arsenic | 401 | Biotite | 70 | | Anakinite | 43 | Arsenic-antimony| 400 | Blumith | 405 | | Anatasite | 333 | Arenschneiderite| 277 | Bismuthine | 462 | | Bismuthite | 325 | Breelite | 389, 109 | Chlorite | 75 | | Bismuth-chlore | 378 | Breelite | 389, 109 | Chlorite | 75 | | Bitumen | 499 | Bleidelite | 316 | Calcite | 30 | | Blendite | 477 | Calamine | 259 | Chondrodite | 169 | | Bole | 127 | Caledonite | 308 | Chonikritie | 95 | | Bollmanite | 103 | Calomel | 367 | Chromite | 335 | | Boracite | 203 | Calcite | 203 | Chrysotrichite | 380 | | Borax | 242 | Cassiterite | 242 | Chrysobal. | 159 | | Bornite | 428 | Celotin | 212 | Chrysocol. | 280 | | Botryogeny | 230 | Cerite | 189 | Chrysolite | 168 | | Boulangelite | 453 | Cervantite | 388 | Cinabar | 487 | | Bournonite | 468 | Cerussite | 303 | Clausthalite | 433 | | Breunnerite | 421 | Chalcolith | 55 | Clypeus | 118 | | Breithauptite | 421 | Chalcolith | 55 | Clypeus | 118 | | Breunnerite | 188 | Chalophyllite | 284 | Clastenite | 83 | | Brewsterite | 49 | Chalopryrite | 427 | Coal, Brown | 497 | | Brechantite | 298 | Chalotrichite | 383 | Common | 496 | | Brounite | 359 | Chalotrichite | 383 | Cobalt, earthly | 371 | | Brounite | 351 | Cobalt | 371 | Cobaltite | 413 | | Mineral | Description | |---------|-------------| | Cobalt-oclore | 371 | | Galena | 431 | | Kermes | 486 | | Nagyagite | 444 | | Pyrargyrite | 482 | | Tachylite | 116 | | Chiliite | 408 | | Calcite | 291 | | Calomel | 59 | | Garnet | 140 | | Kirwinite | 44 | | Kalifeldspar | 437 | | Kyphosilikate | 351 | | Laliolite | 178 | | Columbite | 525 | | Gayusinite | 241 | | Klissanite | 464 | | Nephelite | 92 | | Pyroxomelite | 324 | | Copasite | 157 | | Garvinsite | 24 | | Kleftuite | 129 | | Nephrite | 102 | | Pyrite | 141 | | Copper, Native | 406 | | Geradurodite | 419 | | Kolyrite | 516 | | Nickeline | 302, 422 | | Pyrophyllite | 83 | | Tellurite | 81 | | Coquimbite | 232 | | Gilmonsite | 63 | | Krokyiolite | 113 | | Nitranite | 245 | | Tharsomite | 97 | | Cerdeirite | 166 | | Glauertite | 217 | | Kupferitazig | 441 | | Nickelite | 266 | | Pyrommelite | 80 | | Ceriumite | 217 | | Glassophane | 141 | | Greigite | 169 | | Golinite | 41 | | Neotomagendite | 247 | | Nickelomagnesite | 173 | | Quartz | 1 | | Tetradymite | 447 | | Demarite | 47 | | Gonioline | 70 | | Lamoziette | 34 | | Nissan | 29 | | Hematolobergite | 423 | | Thermortarite | 233 | | Cordierite | 267 | | Gohlartite | 394 | | Latierthamite | 341 | | Nautilite | 19 | | Hematolobergite | 423 | | Thermondrite | 233 | | Crocodile | 322 | | Goetatile | 41 | | Lagi-lazuli | 41 | | Lobritite | 10 | | Neuplar | 888 | | Thordisterite | 175 | | Crostensilithe | 81 | | Goulelle | 430 | | Nolzachemite | 150 | | Obaidite | 15 | | Redrochilite | 440 | | Trombeille | 292 | | Cryolite | 156 | | Graphite | 40 | | Lauramondite | 64 | | Ornichlite | 150.18 | | Rhodlite | 107 | | Tieramennite | 436 | | Cynristile | 36 | | Grimeirodite | 142 | | Lazulnite | 121 | | Omeunite LE150.18 | | Rubrite | 221 | | Tiange | 315 | | Cuprepumbluclite | 432 | | Grünsteine | 418 | | Leuchimomite | 305 | | Olgochalcite | 9 | | Sjögastite | 345 | | Cyanite | 147 | | Gayaklinitte | 509 | | Lead-ethar | 379 | | Oprellite | 238 | | Rock-salt | 76 | | Ultramarine | 420 | | Cyanosite | 234 | | Gynmitte | 85 | | Leuchamelite | 65 | | Onkoinite | 135 | | Rochaillite | 332 | | Uranite | 229 | | Damouricite | 62 | | Dalmatite | 206 | | Hamarium | 337 | | Leuchamontite | 204 | | Opal | 379 | | Roselin | 88 | | Umbleenite | 46 | | Daloyneite | 318 | | Haydingebole | 221 | | Leerupite | 411 | | Orthoclase | 3 | | Triphtyle | 266 | | Dehemitte | 272 | | Halloysite | 123 | | Levryte | 54 | | Osmium-Iridium | 262 | | Troug | 296 | | Dermatite | 187 | | Harnatore | 198 | | Lithostathite | 223 | | Ouërlite | 74 | | Samarallitie | 345 | | Diallique | 106 | | Harlote | 515 | | Livrite | 170 | | Oxalite | 320 | | Sambeline | 243 | | Dialloïtiké | 255 | | Hatchetithe | 513 | | Limonite | 359 | | Ozektarite | 512 | | Scapolite | 17 | | Diamond | 493 | | Hazerlite | 480 | | Lizocline | 416 | | Palagonite | 20 | | Scheelite | 333 | | Uranium-ochrome | 377 | | Diapospore | 161 | | Haumassium | 364 | | Lirenouïtedite | 257 | | Paladium | 201 | | Scheelite-tuhe | 320 | | Dimorphinite | 667 | | Hayoine | 38 | | Lithocannelite | 130 | | Paratsitite | 258 | | Schillerungar | 79 | | Dinotaite | 179 | | Haywardite | 145 | | Lowellite | 232 | | Peatite | 498 | | Schütteritere | 136 | | Dobremité | 187 | | Herschelbite | 61 | | Maraitite | 161 | | Pechuranite | 259 | | Schwartenstein | 45 | | Dokynite | 429 | | Hemzite | 446 | | Magnesbite | 189 | | Potolithite | 53 | | Scrodilite | 256 | | Vivianite | 292 | | Drechite | 508 | | Heudlandite | 174 | | Magneticite | 334 | | Periclase | 153 | | Selenocopaperlite | 439 | | Volborthite | 297 | | Dufrétilite | 267 | | Hiningerite | 171 | | Malachite | 124 | | Pereskite | 452 | | Vaillante | 226 | | Duprefeyolite | 458 | | Horizomnite | 100 | | Manganese, Arsen. | 291 | | Persimmonite | 511 | | Vertreesite | 261 | | Edingtonhite | 58 | | Humboldtellite | 25 | | mureof or | 430 | | Pharmacokoliodrite | 278 | | Siderite | 254 | | Ehlite | 285 | | Huacoalite | 259 | | Cassprous | 368 | | Phenacitite | 163 | | Sillimanite | 143 | | Wagnerite | 33 | | Ekaiaite | 361 | | Hydrargillite | 152 | | Manganite | 363 | | Philippite | 60 | | Silvanite | 463 | | Walechowitzite | 605 | | Ekaollite | 429 | | Hydroboracite | 205 | | Mangan Replacement | 206 | | Pittite | 37 | | Silvernite | 87 | | Water | 523 | | Emerald | 164 | | Hydroboracite | 305 | | Manganosite | 550 | | Photolite | 460 | | Blancaille | 476 | | Woollastonite | 312 | | Energitle | 457 | | Hydrogonzite | 190 | | Margariane | 84 | | Phenginitte | 310 | | Skleroklas | 450 | | Woodswallite | 521 | | Epitidaite | 144 | | Hydrophilite | 91 | | Manganpite | 249 | | Phosphocharcolite | 291 | | Smalbite | 414 | | Epirbidolite | 90 | | Hypersthene | 104 | | Matticotite | 312 | | Plumbosite | 602 | | Zaparose | 134 | | Equatile | 392 | | Morreichaux | 137 | | Pyromaraline | 52 | | Weitzertite | 159 | | Felsipharite | 285 | | Moriamarie | 143 | | Pyrite | 181 | | Taphellite | 37 | | Yorkite | 509 | | Erythrine | 301 | | Idrailite | 518 | | Pandakharite | 383 | | Psophozite | 273 | | Spadinite | 94 | | Wolfsherite | 185 | | Esochrite | 289 | | Imanosite | 341 | | Malanertite | 229 | | Pettitite | 274 | | Spheine | 350 | | Wolfskuppe | 315 | | Eucrase | 163 | | Invararite | 426 | | Melalitone | 519 | | Phlogosite | 452 | | Spinel | 158 | | Wolfsbergite | 366 | | Euflcellentne | 42 | | Iodicite | 328 | | Mendipipte | 311 | | Platina | 390 | | Sphenolite | 152 | | Wolfsbergeritie | 510 | | Eukalrite | 333 | | Iridium | 335, 267 | | Pfelterline | 396 | | Stanulite | 474 | | Eulytine | 176 | | Iris | 358 | | Mercury | 475 | | Pflorite | 129 | | Stannolite | 460 | | Xenithamalite | 455 | | Exensoite | 438 | | Iron | 94 | | Manganese-site | 484 | | Phosphogewise | 301 | | Xenithamalite | 455 | | Falciore | 463 | | JnZeroe | 115 | | Mica, Lith. | 60 | | Pizzaite | 456 | | Solphantite | 379 | | Xenithamalite | 455 | | Faunazolite | 467 | | Jnanosite | 40 | | Potash | 67 | | Pollanite | 362 | | Sternbergite | 473 | | Xenotime | 202 | | Faujasiite | 349 | | Kdlolyte | 503 | | Middletonite | 511 | | Poluxx | 43 | | Sulbine | 449 | | Fischerfelite | 514 | | Johannescline | 450 | | Mooksdalite | 425 | | Polybasite | 472 | | Subhitite | 375 | | Yellow-earthe | 322 | | Fischerite | 31 | | Jonasackite | 227 | | Mussel, Native | 578 | | Pyklarite | 210 | | Trübrite | 210 | | Yttrecretite | 526 | | Fluorosite | 135 | | Johannite | 117 | | Nasqué | 124 | | Pyrolusite | 334 | | Strongewriterte | 439 | | Fluoroselrite | 194 | | Kammererite | 98 | | Mirabellite | 228 | | Porcelain-spar | 36 | | Steantianite | 213 | | Zaconite | 62 | | Frankhünte | 336 | | Kaolin | 117 | | Mispéckel | 412 | | Prehnite | 26 | | Struvite | 223 | | Zincsite | 385 | | Friedelbeinite | 470 | | Kanznitisite | 155 | | Modamite | 412 | | Prounite | 483 | | Salpuck | 491 | | Zincenkalte | 451 | | Fuller's earth | 124 | | Kelzhalite | 154 | | Molybdate-oxide | 448 | | Pelletazite | 93 | | Streckenguhr | 155 | | Kerritel | 13 | | Kaotorite | 13 | | Porfyrite | 161 | | Symporbire | 417 | | Zeolithe | 265 | | Gadolinite | 177 | | Kerato | 325 | | Momorite | 367 | | Pyralliclite | 114 | | Symporbrite | 275 | | Zygoditite | 15 | II. GEOLOGY.

INTRODUCTION.

It is not easy to give an accurate and comprehensive definition of the science of geology; for its nature is so complex and various, that it is difficult, in a few words, either to specify its object or to assign its limits.

It is, indeed, not so much one science, as the application of all the physical sciences to the examination and description of the structure of the earth, the investigation of the processes concerned in the production of that structure, and the history of their action.

We might, perhaps, without impropriety, classify all the physical sciences under two great heads, namely, Astronomy and Geology. The one would comprehend all those sciences which teach us the nature, the constitution, the motions, the relative places, and the mutual action of the Astra, or heavenly bodies; while the other singled out for study the one Astrum on which we live, namely, the earth.

Giving this wide meaning to geology, it would include all the sciences which treat of the constitution and the distribution of the inorganic matter of our globe, as well as those which describe to us the living beings that inhabit it. These sciences are—first, that of chemistry and mineralogy (which may be called one), which teaches us what are the elements of which terrestrial matter is composed, and what are the laws which govern the combinations of those elements into all the variety of known substances, solid, fluid, or gaseous, and the forms, properties, and qualities of those substances; secondly, the science of natural history or biology, the science of life), including botany and zoology in their widest acceptation; and thirdly, that of meteorology and physical geography (which may also be looked on as one), which describes to us the form and disposition of land and water, and air, and the distribution of the temperatures and motions that affect them.

The sciences commonly included under the head of physics, those which teach us the nature and laws of magnetism, electricity, light, heat, force, and motion, would be common ground to geology and astronomy, serving to bind together all human knowledge of matter and its laws into one great whole.

Let it not be supposed that the giving this high place to geology, arises from a wish unduly to exalt it at the expense of the other sciences. Our object is to show that this large view of geology is not only a true, but a necessary one; and that if we do not sometimes look at it from this aspect, we cannot fully describe, nor can the reader rightly understand and appreciate what geology is.

That it is true, is shown by the very fact of the late appearance of geology in the world of science. It was not till some very considerable advances had been made in all the physical sciences which relate directly to the earth, that geology could begin to exist in any worthy form. It was not till the chemist was able to explain to us the true nature of the mineral substances of which rocks are composed; not till the geographer and the meteorologist had explored the surface of the earth, and taught us the extent and the form of land and water, and the powers of winds, currents, rains, glaciers, earthquakes, and volcanoes; not till the biologist (naturalist) had classified, and named, and accurately described the greater part of existing animals and plants, and explained to us their physiological and anatomical structure, and the laws of their distribution in space;—that the geologist could, with any chance of arriving at sure and definite results, commence his researches into the structure and composition of rocks, and the causes that produced them, or utilise his discoveries of the remains of animals and plants that are inclosed in them. He could not till then discriminate with certainty between igneous and aqueous rocks, or between living and extinct animals, and was therefore unable to lay down any one of the foundations on which his own science was to rest.

Neither would it be a satisfactory classification if we were to limit the range of geology to any period of the earth's history; to assign to it, for instance, all time previous to the existence of the human race, and, uniting all the natural sciences under it up to that time, consider it then to be brought to an end, or to split up and diverge into the many independent sciences that concern our contemporary existences, whether organic or inorganic. For not only is there no trace of any hard boundary line between the human and the pre-human period of the earth's natural history; but there appears in each one of the separate natural sciences a perfect blending and continuity from the remotest geological era to the present time. The present is but a part of the past. The inorganic objects we see around us are the result of processes going on in past time, such as are still at work producing the same results; the living beings around us are either the direct descendents of those that lived formerly, or their substitutes and representatives, the living and the extinct forming parts of one great connected series and chain of species, genera, and orders, each of which parts would be incomplete without the other. There is therefore no possibility of making any division in geology such as we are now considering it, or assigning any limit to its range from the earliest period of the earth's ascertainable history to the present moment.

Moreover, as there is no natural science to which the geologist has not to appeal for information upon some point or other in his researches, so there is none which can be fully and completely studied without the help of the geologist, or without including facts or theories which are commonly and rightly reckoned parts of his peculiar intellectual domain. If he has to call upon the professors of each one of the physical sciences in turn, for assistance in his own investigations, he is sure, sooner or later, to repay the obligation by the discovery of a number of facts that enlarge the boundaries of the science he has applied to, or the statement of many problems whose solution throws light upon parts of it that have been hitherto imperfect and obscure.

It is not intended that the reader should infer from what has been said, that in order to be a geologist, he must be thoroughly acquainted with the whole circle of the physical and natural sciences. Such universal acquirement few men have the power to attain to, and of these still fewer retain the ability and the will to make original advances in any particular branch.

No man, however, can be a thorough geologist without being acquainted, to some extent, with the general results of the other sciences, and being able both to understand them when stated in plain untechnical language, and to appreciate their application to his own researches. Such a general acquaintance involves neither profound study, nor requires any great power of mind above the average of hu- man intellect. It is, indeed, what every well-educated man ought to possess.

The necessary preliminary to the science of geology is not the possession of great and accurate knowledge of the whole circle of the natural sciences by any individual persons, but that this knowledge must exist somewhere. Some man or men must have this knowledge, and must be able to combine it, either piecemeal or at once, with the special knowledge of the geologist, before the latter can hope to solve the many difficult and profound problems that arise in the course of his researches.

It may be said with perfect truth, that the geologist is less able than any other student of science to pursue his investigations alone, and independently of the assistance of others; but this is, in fact, only saying in other words that which we are insisting on, namely, that geology in its highest and widest sense embraces all the physical and natural sciences, and is, as it were, made up of them.

If, however, this wide scope be properly given to the term geology, and it be made to include every physical science that treats of anything belonging to the earth, what, it may be asked, is the special business to which the geologist devotes himself as distinct from the follower of other sciences? What is that which he does, and the others do not? Above all, what is that which he teaches to the rest in return for the knowledge communicated to him?

The answer to these questions will show us that there is another and a more restricted sense of the word geology than the wide and general one in which we have been using it. This sense is rather the one formerly attached to the word geognosy, by which we may understand the knowledge of the nature and position of the different masses of earthly or mineral matter of which different districts and countries are composed without reference to the history of their production. This was the early and simple meaning of the word geology, when considered as synonymous with geognosy, namely, the examination and description of the different varieties of rocks and the minerals they contained. Geology was looked upon in the light of a geographical mineralogy, and even yet it is regarded more or less under this aspect by many persons. No one, indeed, could have anticipated, from the mere study of masses of stone and rock, where, to a partial and local view, all seems confusion and irregularity, the wonderful order and harmony which arise from more extended observation and the almost romantic and seemingly fabulous history which becomes at length unfolded to our perusal. To discover the records on which this history is founded, and to understand their meaning aright, frequent, long-continued, and wide-spread observation and research in the field, and patient and conscientious registration and comparison of the observed facts in the closet, are absolutely necessary.

This collection and co-ordination of facts it is which is the proper and peculiar business of the geognost. The ditch, the "cutting," the quarry, and the mine; the cliff, the gully, the mountain-side, and the river-bank; these are his "subjects,"—that which he has to study, to examine, to dissect, to describe the minute of the structures they expose, and to classify and arrange the facts they may afford, depicting their lineaments on maps and sections, and recording them in written descriptions. The business of the geognost, then, is to make out, from indications observed at the surface and in natural and artificial excavations, the internal structure, the solid geometry, of district after district, and country after country, until the whole earth has been explored and described. If, while so doing, he notes all those facts which may enable him or others to understand and explain how that structure has been produced, he then becomes a geologist.

It might at first be thought that in order to make out the solid structure of lands and countries it would only be necessary to understand the nature of the mineral matters of which they were composed, and that for this purpose no knowledge of organic or living beings would be required. It is, however, one of the most remarkable results of geological science that an acquaintance with organic, and especially with animal forms, is at least as necessary for a geologist as a knowledge of minerals, and that a correct knowledge of organic remains (portions of fossil plants and animals) is a more certain and unerring guide in unravelling the structure of complicated districts than the most wide and general acquaintance with inorganic substances.

The cause of this necessity, puzzling and paradoxical enough, perhaps, at first sight, may be briefly stated as follows. When we come to examine the structure of the crust of the globe, we find that its several parts have been produced in succession, that it consists of a regular series of earthly deposits (all called by geologists rocks) formed one after another during successive periods of time, each of great but unknown duration. Now, the mineral substances produced at any one period of this vast succession of ages do not appear to have had any essential difference from those formed at another. We cannot, therefore, with any certainty, discover the order of time in which the series of rocks was formed, or the order of superposition which they consequently preserve with regard to each other, from an examination of their mineral character or contents only. The animals and plants, however, living at one period of the earth's history were different from those living now, and different from those living at other periods. There has been a continuous succession of different races of living beings on the earth following each other in a certain regular and ascertainable order, and when that order has been ascertained, it is obvious that we can at once assign to its proper period of production, and therefore to its proper place in the series of rocks, any portion of earthly matter we may meet with containing any one, or even any recognisable fragment of one, of these once living beings.

Just as when we find under the foundation-stone of any ancient building a parcel of coins of any particular sovereign, we know that the erection of that building took place during his reign; so when we find a fragment of a known "fossil" in any piece of rock, we feel sure that that rock must have been formed during the period when the animal or plant of which that fossil is a part was living on the globe, and could not have been formed either before that species came into existence or after it became extinct. In cases, therefore, where the original order of the rocks has been confused by the action of disturbing forces, or where the rocks themselves are only at rare and wide intervals exposed to view, their order of deposition and consequent succession of place may be more easily and certainly ascertained by the examination and determination of their fossil contents than by any other method.

Practically, it has been found that while a very slight acquaintance with the most ordinary forms of some ten or a dozen of the most frequently occurring minerals is all that a geologist must inevitably learn of mineralogy, the number of fossil animals and plants, with the forms and the names of which he will have to make himself familiar, will often have to be reckoned by hundreds.

This branch of geological knowledge is now known under the name of Palaeontology.

Perhaps, however, the tendency of late years has been to neglect to too great an extent the bearing of mineralogical There are many subjects on which we have still to ask the chemist and mineralogist to enlighten us.

One deficiency which is particularly obvious in Britain is the want of a good and precise nomenclature of rocks, and especially of igneous rocks. Since the publications of Jameson and Maculloch no attempt has been made in English to supply this deficiency, and to bring up our lithological nomenclature to the present state of chemical and mineralogical knowledge. Neither was the want succinctly supplied in any other language till the appearance of the Geisteinlehre of Bernhard Cotta. By the assistance of this and other works we hope, to some slight extent, to supply the deficiency in this treatise.

DISTRIBUTION OF THE SUBJECT.

In order to reduce the great subject of geology to something like order, it appears advisable to divide it into three heads, for which we may use the terms—1. Geognosy; 2. Palaeontology; and, 3. The History of the Formation of the Series of Stratified Rocks.

PART I.—GEOGNOSY.

SECT. I.—LITHOLOGY.

CHAP. I.—ON THE ORIGIN AND CLASSIFICATION OF ROCKS.

Lithology, or the study of the mineral structure of rocks, is based on mineralogy. The number of minerals, however, which enter so essentially into the composition of rocks, as to be called their constituents, is very few when compared with the whole number of minerals known to the mineralogist.

The principal rock constituents are the following.—One simple substance, namely, carbon; one primary compound, silica or quartz, to which, perhaps, rock-salt may be added; and the following secondary compounds, made up of two or more primary compounds, namely, carbonate of lime (calcite or calc spar), sulphate of lime (gypsum), and a number of silicates, which may be grouped under four heads, as the Felspars, the Hornblendes or Augites, the Micas, and the Zeolites.

Crystallization.—One of the most obvious properties of minerals is their crystallization. All crystals are, as it were, built up of minute crystalline particles of like forms, and have been produced by the successive external additions of these minute particles.

It is clear, then, that these particles must have been free to move and arrange themselves; in other words, they must have been in a fluid, or nearly fluid state. But this fluidity may have been the result either of solution in water or other liquids, or of fusion by heat. Whenever, then, we find a crystal or a mineral particle that has an internal crystalline structure, we may feel assured that it has once been either dissolved or melted.

But if this be true as regards individual crystals or crystalline particles, it must be true also of rocks that are made up of such crystals or such particles.

Now some minerals, as, for instance, carbonate of lime, are readily soluble in water containing carbonic acid gas, or in liquid acids; if, therefore, we meet with a rock composed of crystalline particles of carbonate of lime, we could easily believe that it had once been dissolved in water and deposited from that solution.

As regards the solid acid silica, it is also soluble in water containing carbonic acid gas or some other substances, and also when in certain chemical states, and in water at a high temperature. We can therefore easily understand the deposition of crystals of silica or quartz from aqueous solutions.

For the production of many silicates, however (as, for instance, the artificial silicates, porcelain, slag, and glass), great heat is necessary, and the consequent fusion that takes place. We know, also, with regard to many, if not most of the natural silicates, that they are practically insoluble in water, or in any other fluids which are found abundantly in nature.

When, then, we meet with rocks composed altogether of crystals, or crystalline particles, of such silicates, we are compelled to conclude that those rocks were once in a state of fusion from heat.

But in each of these cases we should find gradations from some rocks in which the crystalline particles were large and distinct, through others where they became less and less, and were eventually only discernible with a lens, into some at last which appeared quite compact and homogeneous. The very fact of the gradation, however, would teach us that what was true of the crystalline rocks might also be true of compact rocks of the same mineral composition, and that therefore crystalline and compact limestone, quartz crystals and compact flints, might equally have been dissolved in water, and crystalline and compact silicates equally been melted by heat. In the latter case the artificial silicate glass again assists us, since we know that the very same mass which, if cooled under given circumstances, will form a perfectly homogeneous glass, will, if allowed to cool more slowly, become opaque and stony, and that ultimately it will begin to granulate, that is, its constituents will begin to separate from each other and form distinct crystals in the mass.

Chemical Rocks.—These considerations at once prepare us for the belief that many rocks have been chemically formed, that is, have consolidated from fusion or solution in obedience to chemical laws. Those that have become consolidated from fusion we may call Igneous rocks; those that have consolidated from solution Aqueous rocks.

By Geognosy may be understood the study of the structure of rocks independently of their arrangement into a chronological series, and it might be divided into two parts—Lithology and Petrology. By Lithology is meant the study of the internal structure, the mineralogical composition, the texture, and other characters of rocks, such as could be determined in the closet by the aid of hand specimens.

Under Petrology we may arrange the larger characteristics of rocks, the study of rock-masses, their planes of division, their forms, their positions and mutual relations, and other characters that can only be studied in "the field," but without entering on the question of the geological time of their production.

The subject of Palaeontology will be left for a separate article, but under the head of "History of the Formation of the Series of Stratified Rocks," a condensed abstract of that history will be given, in the form of a chronological classification, mentioning some of the principal and typical groups of rocks known to have been produced at different parts of the earth during each of the known great periods of its existence. Chemically-formed aqueous rocks may be either crystalline or compact.

Chemically-formed igneous rocks may be either crystalline, compact, or glassy.

Both kinds may have occasionally concretionary, nodular, sparry, fibrous, or other textures, according to local modifying circumstances.

In chemical crystalline rocks, whether aqueous or igneous, the external forms of some of the crystals are often very imperfect and sometimes even irregular. Crystals of one mineral having been first formed, prevented the regular formation of the crystals of the other minerals; or the whole mass having crystallized together, the crystals were mutually hindered from attaining their full development by the growth of their neighbours, and all became thus locked and interlaced together in a congeries of mutually imbedded and intertwined crystalline particles.

These crystalline particles, although not perfect crystals, have yet some faces and angles of perfect crystals, being evidently formed in the position where we now find them. They are innate or ingrown crystalline granules.

Loaf-sugar, sugar-candy, crystallized alum, are familiar examples of this structure, and will serve to explain what is meant by the innate crystalline structure of marble or of granite.

Mechanical Rocks.—When, however, we began to study rocks with a view to examine into their mineral constitution, we should soon become aware of another essential difference in them. We should find some rocks the particles of which were large and distinct, but not at all crystalline; or if crystalline internally, we should see that their external form was not regular like a crystal, but exhibited evident marks of mechanical fracture and attrition, of wearing away, or rounding.

The particles of the rocks which are now alluded to, whether internally crystalline or internally compact, are not mutually imbedded and interlaced, like those of chemical rocks, and have no such appearance of having grown where we now find them, but have evidently been brought together from different places, and adhere to each other either in consequence of having been squeezed together by mechanical pressure, or because they are cemented by some other substance which serves to bind and unite them to each other.

In these rocks the particles are generally more or less rounded and smoothed externally, as if water-worn.

This water-worn form and derivative origin is very obvious with respect to some of these rocks, which consist of pebbles or rounded fragments of other rocks, compacted together in sand, which is clearly the result of the rounding process.

In many cases the very rock from which the pebbles were derived can be pointed out, and the distance, therefore, which they have been carried is known. In other cases the fact of mechanical transport is equally obvious, though the original site may be unknown.

From those cases where the particles are large and their form distinctly visible, there is every gradation through those where they become less and less, till at length they are not discernible by the lens. We have, then, compact derivative rocks just as we have compact chemical ones.

To all such derivative rocks we may with great propriety assign the term Mechanical, as showing that their materials have been mechanically transported to their present sites.

The machinery employed in this transportation must clearly be either currents of water or currents of air, and the mechanical rocks, therefore, must be all either Aqueous or Aeriel rocks, the latter being very few and unimportant compared with the former.

Even with regard to igneous rocks, which must in themselves be purely chemical compounds, they still may have their mechanical accompaniments whether they were formed in the air or in the water, as we see in the case of the ashes, cinders, and fragments blown from the mouths of volcanoes.

Organic Rocks.—There is yet another source from which some rocks are derived, inasmuch as some are found to be wholly, or almost wholly, composed of fragments of animals or plants. These rocks may be termed Organic, in the sense of organically-derived rocks.

The portions of the plants or animals may be either little altered from their original condition, or very much altered and altogether mineralized. In the first case, they belong perhaps more particularly to the mechanically, in the latter, to the chemically, formed rocks.

Mixtures.—As, moreover, chemical precipitates are liable from many causes to be adulterated with mechanical impurities, and mechanical deposits to be impregnated with chemically acting gases or liquids, and as both mechanical mixtures and chemical actions and reactions may play a part in the formation of rocks made of organic materials, we can easily see how all three classes of rocks may occasionally be mingled together and pass into each other, and how many aqueous rocks may have been formed by the union of two or of the three agencies, and appear to belong to one or the other class according to the point of view from which we observe them.

We have now arrived, then, at the conclusion that different rocks had an aqueous, an igneous, or an organic origin, solely from the consideration of the nature of the mineral particles composing them. This conclusion, however, by no means depends entirely on such considerations. The aqueous rocks are known to be so, not only from their being composed of soluble minerals, or of minerals that have been water-worn, or parts of plants and animals that have either lived in water or been carried down into it, but also because their materials are arranged in regular layers and beds or strata, obviously the result of their having been regularly strewn out over the bottom of the seas and lakes in which they have been deposited. They are hence often called Sedimentary and Stratified rocks.

The igneous rocks, on the other hand, are many of them such as we see now to be poured forth from the mouths of volcanoes in the state of molten lava; others again are closely allied to these, and there is a regular chain of gradation from these through their whole series.

Those which least resemble actual lava are found sometimes to have been injected, in the form of veins and tortuous strings, into the cracks and crevices of other rocks, or to have cut through them in great wall-like masses called "dykes" just as lava does. In many of these cases they have exerted just such an influence on the rock they came in contact with as great heat would have exercised. The neighbouring rocks have in fact been burnt, and are sometimes greatly altered from their original state as seen at a distance from the igneous rocks.

Metamorphic Rocks.—This fact, together with the consideration of the chemical actions and reactions that may be set up in the mass of rocks by the percolation of various fluids or gases, and the mechanical or chemical forces that may be brought into play by the action of pressure and other agencies, naturally disposes us to ask the question,—Whether many rocks as we now see them may not be in a very different state from that in which they were originally formed? We should ultimately find reason to answer this question in the affirmative, and introduce another class under the head of Metamorphic (or transformed) rocks, to include those which had, by means of subsequent alteration, acquired any essentially different characters from their original ones.

Guided by these considerations, we may class all rocks whatever under the four great heads of Igneous, Aqueous, Aerial, and Metamorphic.

The Igneous are almost entirely chemically-formed rocks, but some of their varieties have their mechanical accompaniments.

The Aqueous rocks are either chemical, mechanical, or organic, those of mechanical origin being far the most abundant, although not the most important kinds.

The Aerial are all mechanical.

The Metamorphic are either those in which the original structure and composition are still obvious, or those in which those characters are altogether obscured and replaced by others produced either by heat, or pressure, or both combined.

We shall commence with the description of the igneous rocks, because these may be looked upon as those most essentially original and self-subsisting, or most independent of the others.

Before entering on the technical description of rocks, however, it will be as well, perhaps, to define exactly, what we mean by the term rock.

A mineral is an inorganic substance that has a definite chemical composition, and a regular and symmetrical form; each of the particles of which it is made up exactly resembling all the other particles.

A rock is a mass of mineral matter consisting of many individual particles, either of one species of mineral, or of two or more species of minerals, or of fragments of such particles. These particles need not at all resemble each other either in size, form, or composition; while neither in its minute particles, nor in the external shape of the mass, need a rock have any regular symmetry of form.

Geologists are accustomed also to include under the term rock, all considerable accumulations of mineral matter, whether they be hard or soft, compacted or incoherent. In this sense soft clay, loam, or loose sand, may be called "a rock."

CHAP. II.—IGNEOUS ROCKS.

The igneous rocks are divided by Sir C. Lyell and others into two classes—the Volcanic and the Plutonic. Such a classification is theoretically correct, as separating those formed at the surface, in air or water, from those formed deep in the earth; but practically we often meet with rocks that it is difficult to place with certainty in either class. It is, moreover, often advisable to avoid terms that involve theoretical or foregone conclusions. For these reasons we should prefer, with Sir R. I. Murchison and others, to arrange the igneous rocks under three heads—Volcanic, Trappean, and Granitic; taking the middle term, Trappean, as one of convenience only, to include some that are possibly volcanic, some that are more essentially granitic, with many intermediate or undetermined rocks between the two.

Igneous rocks differ among each other—

1st, As being made up of different minerals.

2d, As having different textures.

The three principal varieties of textures are the crystalline (or granular), compact, and glassy.

When a rock is distinctly granular, so that the crystals of its mineral constituents are clearly discernible, they may be determined by simple inspection. In the compact and vitreous textures, however, the determination of the mineral constituents of a rock can only be arrived at by chemical analysis. This will enable us to find out of what substances the rock consists, and what are their proportions; and the consideration of these proportions, and the comparison of them with those forming different minerals, will enable us to determine with greater or less certainty of what minerals the rock is composed, or, at all events, what minerals it would probably form if they were allowed to develop themselves.

It has been shown from the processes of the manufacture of glass, that the very same molten mass of silicates would form transparent glass, opaque slag, or crystalline stone, according to circumstances. As these different conditions of texture receive different names, so may the different textures of natural substances receive different names, notwithstanding that in some cases they consist of essentially the same ingredients.

As some slags become porous, or vesicular, and thus pass into cinders, so some igneous rocks likewise assume a vesicular or cindery texture.

When the pores or vesicles become filled with a crystalline nucleus or kernal of any mineral, either by subsequent infiltration, or during the process of consolidation, so that the dispersed crystalline patches look like almonds stuck into the mass, the rock is said to be amygdaloidal.

When single detached crystals are disseminated through a compact base, or large crystals through a fine-grained base, the rock is said to be porphyritic. The term Porphyry, then, which has been often used as a designation for a particular class of rocks, will here be used chiefly, or solely, to distinguish this variety of texture, which is one that may occur in every kind of igneous rock.

From what has been said before, it may be inferred that all igneous rocks without exception are composed of minerals which are silicates.

These minerals may be said to belong to two great classes,—silicates of magnesia and silicates of alumina,—the species or varieties of each resulting from their various mixtures with silicates of potash, soda, lime, iron, manganese, &c. The silicates of magnesia, &c., constitute the hornblendic, or pyroxenic, or augitic minerals; the silicates of alumina, &c., forming the feldspathic ones. The micaceous minerals, which we may look on as resulting from mixtures of the two, or as holding an intermediate place between them, are in reality of minor importance so far as unaltered rocks are concerned.

The feldspars are the basis of all igneous rocks, those in which no feldspar of any kind is present being very few and unimportant, even if they exist at all. The hornblendic and augitic minerals hold the next most important place; and the volcanic and trappean rocks may be divided into two great series depending on the amount of those minerals which are mingled with the feldspars. Those rocks in which feldspar alone occurs, or in which it greatly predominates, may be called the feldspathic rocks; those in which the hornblendic or augitic minerals play a considerable part may be called hornblendic or pyroxenic rocks. It must, however, be clearly borne in mind that feldspar in some form or other is always the basis of the latter, while hornblende and augite in any form are often entirely absent from the former.

I.—THE VOLCANIC ROCKS.

These are often spoken of under the general term of Lava. They include, however, some that would be more commonly described as trap rather than lava, and others, such as tuff and ashes, which could not strictly be called by either name.

The volcanic rocks have been classified by Abich under three heads,—Trachyte, Dolerite, and Trachy-dolerite. Bunsen, also, in his Memoir on the Volcanic Rocks of Iceland, gives a similar classification, describing his normal Geology. trachytic rocks as one end of the series, and his normal pyrozeic rocks as the other end, with many intermediate varieties between the two.

Bunsen gives us the following as the mean value of the composition of his two normal rocks:

| Normal Trachyte | Normal Pyrozeic | |-----------------|----------------| | Silica | 76-07 | | Alumina and prototide of iron | 14-23 | | Lime | 1-14 | | Magnesia | 9-28 | | Potash | 3-20 | | Soda | 4-18 |

He then shows that, by analyzing any intermediate variety of rock, and determining the proportion of any one of these ingredients (taking the silica as the easiest and best), the proportion of the other ingredients may be calculated, and thus may be determined the quantities of these two normal substances which have been mixed together to form the rock in question.

In the following descriptions of the volcanic rocks we are largely indebted to Cotta's Geesteinslehre, to the Introduction to Daubeny's Volcanoes, and to the last chapter of the third volume of D'Archiac's Histoire des Progrès de la Géologie.

The Trachytes are so called from the Greek word τραχύς, rough, as they commonly have a rough prickly feel to the finger. They are usually light-coloured, pale gray, or white, but sometimes dark gray and nearly black. They are composed principally of feldspar,—the feldspar being one of the varieties that is rich in silica, such as orthoclase, adularia, or albite, and not any of those in which the bases are more abundant, such as labradorite or anorthite.

As Trachyte is made into a class as well as a species of rock, we may similarly elevate Dolerite.

The Dolerites, so called from the Greek δόλης, deceptive, are usually of a dark green or black colour, weathering brown externally. They are commonly heavier than the Trachytes, as containing a less proportion of silica and a greater one of the heavier bases.

They are composed partly of a feldspathic and partly of an augitic or pyroxenic mineral, the feldspar being commonly, though not perhaps invariably, one of the more basic silicates, such as anorthite or labradorite.

The Trachytes, or Feldspathic Lavae.

1. Trachyte, properly so called, has either a fine-grained or quite compact texture, a harsh feel, and sometimes a cellular and scoriified appearance. It varies in colour from a pale gray to dark iron gray, and is sometimes reddish, from the presence of iron. It is composed of a confused aggregation of crystals of feldspar, often minute and needle-shaped, but with others larger and more distinct.

This feldspar is said to be commonly potash albite (or periclase), and glassy feldspar (or adularia), in which some of the potash is replaced by soda. Crystals of mica and hornblende are often present, and sometimes even of augite, the whole either confusedly united without cement, or embedded in a feldspathic paste, either cellular or compact.

2. Trachytic porphyry has seldom a scoriified aspect, looking often more like a plutonic than a volcanic rock, as that of the Pic de Sancy, and the Roc de Cacadogne, of Mont Dor, which at first sight resembles granite in external appearance.

Crystals of glassy feldspar, sometimes small, but sometimes as much as half an inch long, white or flesh-coloured, are set in a compact light-coloured feldspathic paste, with brown mica, and sometimes also with crystals of quartz.

Many varieties of trachytic porphyry contain a number of very small globules, which seem to consist of melted feldspar, having often in their centre a little crystal either of quartz or mica. The assemblage of these globules leaving minute cells between them, sometimes gives to the rock a scoriified aspect." (Daubeny.) Chalcedony occurs in small geodes, and sometimes intimately mixed with the paste in which the crystals are imbedded.

Trachytic porphyry passes sometimes by insensible gradations into—

3. Pearlstone, which is composed of a number of globules from the size of a nut to that of a grain of sand, of a vitreous or enamelled aspect, and pearly lustre, adhering together without any paste.

These sometimes lose their lustre and size, and pass into a compact stony mass, or change into globules of feldspar, compact, or radiated—the whole rock being composed of them. Many variations occur; the whole sometimes becoming fibrous, cellular, spongy, and passing gradually into pumice.

4. Domite is a grayish white, fine-grained, compact, earthy, and often friable variety of trachyte. It frequently contains flakes of brown mica.

It appears to be a decomposed trachyte, in which the feldspar is affected, but the mica not. The passage of muriatic (hydrochloric) acid is, by some, supposed to have affected this transformation. It is a remarkable rock, but not one of general occurrence beyond the district of the Puy de Dôme, in France.

5. Andesite, a trachytic rock, found at Chimborazo and other parts of the Andes; has white crystals resembling albite in a crystalline base of a dark colour. It has various degrees of compactness and consistency, and has a coarse conchoidal fracture.

Small crystals of glassy feldspar occur, though rarely, but those of hornblende are common; and augite is also present sometimes. From the predominance of hornblende it sometimes passes into a diorite or greenstone.

6. Clinkstone or Phonolite is a compact homogeneous rock, with a scaly or splintery fracture, sometimes conchoidal, of a grayish green, or ashy grey colour, both weathering white externally. It is often rendered perphyritic by scattered crystals of glassy feldspar, but these are commonly not very distinctly separable from it, appearing only as brilliant surfaces here and there in the mass. Hornblende, augite, and magnetic iron are rare in it. According to Gmelin it consists of a mixture of glassy feldspar, with a zeolite in variable proportions. It may, therefore, be formed from trachyte by the addition of sea-water; the soda of which, combining with some of the orthoclase, would make glassy feldspar, while the water, combining with the other constituents, would form a zeolite. (Abich, in D'Archiac, vol. iii., p. 604.)

Clinkstone commonly splits into thin slabs, and is often so finely laminated as to be used for roofing slate. The slabs give a metallic sound when struck with the hammer, whence its name. It is sometimes perfectly columnar; the columns splitting across into slabs, which are also used as slates. It may, however, perhaps be doubted, whether many of the so-called volcanic clinkstones really contain water according to the definition, and whether they are not a flaggy, or laminated variety of compact trachyte.

7. Obsidian, or Volcanic glass, is the vitreous condition of a trachytic rock. It is said to be necessary for its natural production that the rock should be composed of minerals rich in silica, or "trisilicates;" the simple "silicates" or "bisilicates" of alumina, being incapable of forming obsidian. (Daubeny, p. 16, 2d edition.)

8. Pumice is the cellular and filamentous form of obsidian, and the same remarks as to origin will apply to it.

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1 Geodes are rounded concretions, generally hollow, and containing crystals. They are sometimes called "potato stones" from their size and shape.

2 Without disputing the truth of the origin here assigned to all naturally formed obsidian, it is yet equally true, that basalt can be artificially converted into obsidian, by simple melting and rapid cooling. Messrs Chance of Birmingham now melt the basalt of the Rowley Hills by simple heat without the addition of any foreign ingredient, and cast it into blocks and ornamental mouldings for architectural purposes. Portions which are allowed to cool rapidly, The Dolerites, or Augitic Lava.

9. **Dolerite**.—A crystalline, granular, distinct mixture of labradorite and augite with some titaniferous magnetic iron ore, and also often with some carbonate of iron and carbonate of lime. General colour dark gray.

The labradorite forms white or light gray tabular crystals, and the augite black columnar ones. Both can easily be distinguished by the naked eye, especially in the coarser varieties. The magnetic iron forms small octohedral scarcely visible grains, which can be recognised only by the magnet. (Cotta.)

Cotta mentions a variety from Auglasse near Liegfried, which contains 28 per cent of the carbonates, three-fourths of that being carbonate of iron.

10. **Anamesite** is properly only a fine-grained dolerite, so fine-grained that we can only distinguish the fact of the granular texture, and no longer recognise the individual minerals. Its colour is dark grey or greenish or brownish black. It forms the intermediate step between dolerite and

11. **Basalt**, which is a compact, apparently homogeneous, nearly or altogether black rock, with a dull conchoideal fracture. It often contains crystals or grains of augite, olivine, or magnetic iron, and is sometimes vesicular or amygdaloidal.

The knowledge of the composition of basalt dates from 1836, when Gmelin showed that it was, like phonolite, an intimate mixture of one part that was decomposable in acid and another not decomposable. The decomposable portion is partly of the nature of a zeolite, partly of that of labradorite; the undecomposable portion is augite. (Cotta.)

Basalt, therefore, as it contains water in its zeolitic portion, bears the same relation to dolerite that clinkstone does to trachyte.

The three rocks above mentioned differ rather in texture than in mineral composition. In the two following rocks another feldspathic mineral is substituted for the labradorite.

12. **Nepheline Dolerite** is a crystalline granular mixture of nepheline, augite, and some magnetic iron. (Cotta.)

13. **Leucite Rock** is a crystalline granular, porphyritic-like, or even a compact, aggregate of leucite, augite, and some magnetic iron; generally gray. (Cotta.)

Trachy-dolerite, or Intermediate Lava.

These rocks, from their very nature, do not admit of any precise definition or nomenclature. The rocks already named and described are mixtures of various minerals. When those mixtures are in anything like definite proportions, and the minerals are well characterized, the rocks assume a particular character, and are capable of definition. When, however, the mixtures become indefinite, and the minerals begin to pass one into another, or are so intimately blended that they cannot be distinguished, attempts at definition only lead to confusion instead of order, and encumber the memory rather than assist it.

Instead of separating these blending rocks, then, and distinguishing them by different names, it is better to follow the example of Abich, and unite them under one term, such as that proposed by him—14. Trachy-dolerite.

Neither is this a mere evasion of a difficulty, since the things themselves are so similar, both in substance and in origin, that the creation of distinct names would be merely making distinctions where no real or essential difference exists.

It may be useful, here, perhaps, to give Abich's table of the specific gravity, and the percentage of silica of some of the above rocks, arranging them according to the latter character.

| Specific Gravity | Percentage of Silica | |------------------|---------------------| | 1. Porphyritic trachyte | 2-5783 | 69-45 | | 2. Trachyte | 2-6821 | 65-85 | | 3. Glassy andesite | 2-6851 | 65-55 | | 4. Domite | 2-6334 | 65-50 | | 5. Andesite | 3-7032 | 64-45 | | 6. Phonolite | 2-5770 | 57-65 | | 7. Trachy-dolerite | 2-7812 | 57-65 | | 8. Dolerite | 2-8013 | 53-09 |

From this it appears that the percentage of silica in porphyritic trachyte is equal to that of albite; in trachyte and andesite, equal to that of orthoclase; and in dolerite, equal to that of labradorite. Trachy-dolerite, intercalated among the rocks, as andesite and oligoclase are between potash albite, and labradorite among the feldspars, shows the passage from one to the other. Lastly, with only two exceptions, the above table shows us that the specific gravity increases as the percentage of silica diminishes; and Abich, therefore, says that the determination of these two characters, joined to the observation of the mineralogical constituents, will suffice to determine with precision to which kind any volcanic rock belongs.

There is yet another variety of volcanic rocks to be considered, that, namely, called Tuff or Peperino.

15. **Tuff** (ash) is ordinarily the ashes, dust, and powder, mixed with little lapilli and coarser fragments, blown from a volcanic focus, and falling either on the land or into the sea. If it fall on the land it may become compacted into a rock, either by the simple pressure of its own weight, or in consequence of the percolation of water containing mineral matter in solution. This water may either be rain falling with the ashes, or rain or other water subsequently gaining access to them. If the ashes fall into the sea they become subject to the conditions under which all other mechanically-formed aqueous rocks are produced. In this case tufts often contain fossil shells.

Abich describes the trachytic tufts of the neighbourhood of Naples as of two sorts,—one inferior, of a clear straw-colour, characterized by fragments of glassy feldspar, augite, and hornblende; the other, upper tuff, being white, in thinner beds, and with much pumice.

Bunsen, in his description of the volcanic rocks of Iceland, seems inclined to attribute a metamorphic origin to tufts, and to derive them from the decomposition or alteration of the pyroxenic rocks of that island. He calls them palagonitic tufts, the mineral palagonite (a hydrated silicate of alumina and lime) being an essential constituent of these tufts both in Iceland and in Etna, as shown by Walterhausen.

He refers to Darwin's observations on a basaltic lava which has covered over limestone at Port Praya (C. de Verde Islands), and says that the lava, when in contact with the limestone, possesses all the characters of palagonite.

Without denying that some tufts may have been formed from the decomposition of tufts of actual lava, we are still inclined to look upon that as the exception rather than the rule, and to believe that tuff in general is a mass of volcanic "ash," deposited mechanically, however it may have been subsequently modified either by igneous or aqueous agencies.

Some geologists confine the term tuff to trachytic masses, and use the word "peperino," to designate those derived from pyroxenic (or augitic) rocks.

Tufts and peperinos, from the nature of their origin, must have a great variety of character, from a fine-grained compact stone to a coarse breccia or conglomerate, and from a loose incoherent accumulation to a hard tough stone.

Immense piles of volcanic sand and gravel, and great breccias composed of large semi-angular fragments, also not unfrequently occur, which would hardly be called tuff, but which must not be altogether omitted in our enumeration of volcanic rocks.

II.—TRAPPAN ROCKS.

We have before said that we adopt this designation as a convenient one only, and for the same reason we would extend it. The word "trap" has hitherto been considered to be strictly applicable only to hornblende or augitic rocks. It is derived from the Swedish *trappa*, a stair,—those rocks being supposed usually to assume a step-like form. The term, as thus derived, is, however, no more exclusively applicable (except from custom) to the hornblende than to the feldspathic igneous rocks, and has been often used vaguely to designate any igneous rocks which could not be said to be distinctly granitic on the one hand, or absolutely volcanic on the other. In this vague and general sense we shall here use it, its very vagueness being its recommendation as best adapted to receive a class of rocks that do not admit of any strict definition or circumscription.

As the volcanic rocks are divisible into three heads,—Feldspathic, Augitic, and Intermediate,—so we may conveniently divide trappan rocks into three similar heads,—Feldspathic, Hornblende, and Intermediate. For the two first of these the general designations, Felstone and Greenstone, may be used,—felstone corresponding to trachyte, and greenstone to dolerite. It is not easy to make a combination of words answering to Abich's trachy-dolerite, but the intermediate rocks exist in abundance which would be comprised under such a designation.

Felstone is a name taken from the German *Feldstein*, and proposed by Professor Sedgwick to designate a class of igneous rocks to which many titles have been given, but which have never, we believe, been yet properly examined and described. Compact feldspar, petrosilex, and cornean, are among these names, as well as the hornstone of some geologists, though that name has also been applied to chert.

**Felstone or Feldspathic Traps.**

16. Felstone is a compact, smooth, hard, flinty-looking rock.

It has two principal varieties,—the pale green, passing into a greenish or yellowish white; and the blue or gray, varying from pale to dark gray. The gray or blue variety weathers white, its external margin being white sometimes to the depth of a line, sometimes to that of an inch or two. Some blocks that appear wholly white have a small blue patch in the centre. The green or greenish white variety is often very translucent at the edges; the gray is commonly opaque. The fracture is generally smooth and straight, seldom conchoidal; but in some of the blue or gray varieties it is rough and splintery. It often splits into small slabs, and sometimes, especially the green kinds, into laminae.

The fragments sometimes ring with a metallic sound like clinkstone, and many so called clinkstones (such as those of the Roche Sandalire and Tuilliere in the Mont Dor district, and those of the Velay) are almost undistinguishable by any external characters from many of the felstones of Wales and Ireland.

In many felstones, both in North Wales and South Ireland, lines and striæ, resembling lines of lamination or deposition, of slightly different colours, can be traced through the mass of the rock, sometimes straight, sometimes less wavy and tortuous, like the variously banded lines and bands in a slag from an iron furnace, and resulting, probably, like them, from the motion of the mass when in a pasty and semi-fluid condition.

In the most smooth and compact varieties, the lens will often disclose small shining facets of crystals of feldspar, and these become larger and more numerous till we reach the completely granular and crystalline felstones. Small crystals or crystalline portions of quartz also are occasionally present in most varieties.

Sometimes the rock becomes nodular and concretionary, the nodules varying in size from that of a pea to that of a man's fist, either scattered in a compact or powdery base, or touching each other and making up almost the whole mass of the rock. The substance of these nodules is sometimes the same as that of the base, but in some instances they are hollow, and contain crystals of quartz and other minerals, and also a soft, dark green earth. In this respect it seems to resemble the rock previously described as pearlstone, though it never has any pearly or other lustre.

Felstone as thus described is probably a mixture of a feldspar with silica in a state of paste. We may look on it as a compact form of trachyte, more or less altered by pressure, or other agencies, and containing a larger proportion of silica. It passes from that state to one in which the minerals are crystallized out more or less completely, becoming first a granular and crystalline felstone, and then a granular aggregate of crystals of feldspar and quartz, passing into a quartziferous porphyry.

This latter is the rock known in Cornwall as elvan, and we think, as a convenient designation, "elvanite" might be adopted as a name for it and its varieties.

17. Pitchstone appears to be a variety of felstone, having a more vitreous character, and a resinous lustre; whence it derives its name. It is of many colours, varying from black to green, gray, and yellow. The black varieties look, however, more like hornblende or augitic mixtures than purely feldspathic rocks.

Clinkstone is frequently spoken of as a trappan as well as a volcanic rock, but it is probable that many of the rocks so described would not come within the definition of clinkstone given before, and are only platy, flaggy, and laminated (perhaps even "cleaved") varieties of felstone. There may, however, be other true trappan clinkstones, the hydrated varieties of felstone, just as volcanic clinkstone is a hydrated trachyte.

18. Felstone porphyry, or Feldspar porphyry, is a rock consisting of a base of compact felstone, with distinct scattered crystals of feldspar embedded in it. The base is commonly either of a dull green, gray, or red colour, and

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1 Felstone, as here described, is a very abundant rock among some of the older formations in the British Islands, making up whole mountain masses; but it appears to be little known or remarked on the Continent, as Cotta speaks of it as only rarely seen and in small quantity, and but two specimens of it occurred in a collection of 660 igneous and altered rocks purchased from Krantz of Berlin.

* Professor Haughton has recently analyzed some specimens of Irish felstone, and has found in them such an amount of silica as confirms the view commonly entertained of this rock, that it is a mixture of feldspar and quartz. His results, as given to the Geological Society, Dublin, in a recent paper, are—

| Felstone of Ballymurtough, county Wicklow. | |---------------------------------------------| | Quartz | 45-54 | | Feldspar | 54-16 |

| Felstone of Knockmahon, county Waterford. | |-------------------------------------------| | Quartz | 40-81 | | Feldspar | 57-19 |

| Felstone of Benamore, near Killarney. | |-------------------------------------------| | Quartz | 20-51 | | Feldspar | 77-85 |

This superabundance of silica in these old igneous rocks, so far beyond that which is found in any trachyte, is certainly a very curious subject for speculation.

Could they ever have flowed at the surface with their present constitution? Has their composition been changed, by aqueous metamorphoses or otherwise, since their formation? the imbedded crystals are commonly white or flesh colour, or some other shade generally contrasted with the base by being of a paler hue.

19. Quartziferous Porphyry (Elvanite) has the same base, or a granular one of the same materials, with disseminated crystals or crystalline grains of quartz.

Greenstone, or Hornblende Trop.

Greenstone is an old and well-known name for a numerous and important class of trappean rocks. It is a translation of the German Granitstein, and synonymous with the French Diorite.

20. Greenstone, or Diorite, consists of a mixture of feldspar (orthoclase) and hornblende, varying in texture from a fine-grained compact rock, in which the crystalline state of the minerals is barely discernible with a lens, to a coarsely crystalline aggregate. Its colour is generally a dull green, varying from light to dark green, sometimes almost black. In some varieties, on the other hand, where the feldspar is very white and in great quantity, the rock might almost be described as white, speckled with dark green spots. It weathers to a dull dark-coloured brown, the weathered blocks being generally massive and well rounded, and covered with patches of white lichen. On breaking open the weathered part of a greenstone and testing the rock with acid, we almost invariably find that it will effervesce along the inner border of the weathered portion. Many Greenstones, also, even when apparently unweathered, effervesce with acids along the minute cracks and pores in the mass.

The feldspar of greenstones is commonly presumed to be orthoclase, but is, perhaps, often albite; and in some of the rocks which come under this head augite or hypersthene is substituted for hornblende. Mica, of a dark brown colour, sometimes occurs (as in some of the Wicklow greenstones), either in distinct plates, or as coating the surfaces of small crevices or those of the other crystals.

M. Delesse says that many rocks hitherto classed as greenstone contain no hornblende, their green colour being the result of the greenness of some of the feldspar composing them. These, then, would probably come under the head of one of our crystalline felstones.

Greenstone, like felstone, becomes sometimes porphyritic, in consequence of one or other of its constituents forming distinct crystals in a compact mixture of the rest, or larger disseminated crystals in a granular crystalline base. When the greenstone is quite compact and dark coloured, it is not, perhaps, very easy to distinguish it from basalt by any external characters.

21. Melaphyre is a name for a black porphyritic rock, containing crystals of augite or oligoclase, in a base of augite and labradorite or oligoclase.

Under the general head of Greenstones and Melaphyres, Cotta describes the following rocks:

22. Diabase.—A crystalline granular, sometimes porphyritic, or even a slaty, mixture of augite and labradorite or oligoclase, mostly with some chlorite.

23. Calcediabase.—A finer-grained, or entirely compact diabase, with traces of calcspar.

24. Gabro, Euphoidite, Diabase rock.—A crystalline granular mixture of labradorite or sanamite, and diabase or smaragdite.

25. Hypersthene, and Hypersthene rock.—A crystalline granular mixture of labradorite and hypersthene.

26. Augite rock, Lherzolite.—A coarse-grained to compact rock, consisting essentially of augite alone. Rare. Lherz in the Pyrenees.

27. Novite is a name of Esmark's for a rock yet undetermined; some of its characters seem to belong to diorite and some to gabbro.

28. Diorite.—A crystalline granular mixture of hornblende and albite; sometimes even slaty or porphyritic.

29. Glaucite Diorite, Glaucular Greenstone, Cornish Granite.—A crystalline granular mixture of grayish white feldspar (amphibole), dark gray hornblende, and some quartz, in which alternating concentric layers of hornblende and feldspar form globular concretions from one to three inches in diameter.

30. Micaceous Diorite.—A crystalline granular mixture of hornblende and oligoclase, orthoclase, quartz, and mica. Mostly dark, or quite black.

31. Hornblende rock, Amphibolite, consists essentially of hornblende alone, which forms sometimes a crystalline granular, sometimes a quite compact aggregate.

32. Keratzen.—A crystalline mixture composed essentially of hornblende and mica, in which, however, some feldspar is often mingled. In the latter case it effervesces slightly with acids.

33. Eclogite.—A crystalline mixture of green smaragdite and red garnet. The garnet occurs as porphyritic crystals in the fine-grained base of smaragdite.

34. Diatone rock.—Principally composed of diatone, with which, however, some garnet, mica, or smaragdite is mingled.

35. Aphanite, Melaphyr.—A compact or fine-grained, dark gray, brown, or black rock, which apparently consists principally of a feldspathic mineral intimately mixed with augite, hornblende, magnetic iron, and the like. Its exact mineralogical composition is not yet determined. It is sometimes vesicular, amygdaloidal, or porphyritic, and is even said to be sometimes slaty.

36. Serpentine.—A compact, mostly green or brown rock, consisting essentially of the mineral serpentine only. Fracture splintery and dull, easily workable and unctuous to the touch. A variety of serpentine is Schiller rock, which contains crystals of Schiller spar.

37. Garnet rock.—A crystalline granular, but very unequal mixture of garnet, hornblende, and magnetic iron.

38. Bullate.—A mixture of olivine-like oxide of iron, green augite, and brownish-red garnet.

39. Epidote rock.—A granular compact, or variolitic mixture of pistacite (green epidote) and quartz.

40. Labradorite rock.—A crystalline aggregate of labradorite, with interspersed crystals or crystalline particles of dark hornblende. As a rule, it also contains small crystals of iron pyrites.

Basalt, like clinkstone, must also be enumerated among the traps as well as among the lavas, since it may be very difficult to say, with respect to some masses of basalt, that they were ejected from what might be truly described as a volcano.

Claystone, or Wacke, is sometimes spoken of as a trappean rock. It is probably either a compact basalt or greenstone, in a decomposed and earthy state, or an ash partially hardened and consolidated.

The traps, both felstone and greenstone, are accompanied, like the volcanic rocks, by their respective ashes or tufts.

41. Feldspathic ash is usually a rather coarse-grained flaky-looking rock, of a pale green, pale gray, or white colour. It has often a soapy feel to the touch, and would be then called chlorite-schist by many persons. It is commonly to be easily detached in flakes, which are quite translucent, and can be as easily ground down into powder. Other varieties are much harder and more compact; and there is, in fact, every gradation from a soft ash into a compact felstone, undistinguishable from solid trap.

Some of these solid-looking traps, however, show casts

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1 We have included serpentine among the trappean rocks, as there may doubtless be injected masses entitled to the name. Many serpentines, however, are only metamorphosed magnesian limestones, a fact which was confirmed to us by Sir W. Logan in 1854, from his observations in Canada.

2 Professor Sedgwick uses the term "schalzstein" to designate these ashes, translating it by "trap shales" instead of ash. If, however, we use the term "ash" in a technical sense as the translation of tuff, there does not appear any valid objection to it. The specimens of German "schalzstein" which we have seen are not the same as any of the British "ashes" we are acquainted with. of fossils, and contain angular fragments of slate and other rocks, clearly betraying their mechanical origin. Some even contain crystals of feldspar, making the rock look like a porphyry, until closely examined, when the crystals are found to have their angles worn, and to have been more or less weathered and rounded before they were included in the base.

Along with these also, there generally occur angular or rounded fragments of felsite, slate, or other rocks, of every size up to blocks of 6 or 8 inches in diameter; the rock then becoming a trappean breccia or conglomerate, with either a hard and compact or a loose and flaky base.

Sand is sometimes mingled with this base; and there is then a passage from ash, through sandy ash and ashy sandstone, into pure sandstone.

It is rare to find a genuine ash that will not effervesce slightly with acids. The nodular concretionary structure, which we have previously mentioned as occasionally to be seen in some felsites, likewise occur in felsite ash. At least, the base in which the nodules lie is often of that flaky slightly coherent character which is characteristic of ash.

42. Greenstone ash is perhaps still more various in composition than that of felsite.

One well-marked variety is a quiet compact rock, of a pale greenish brown hue, speckled with small black spots.

Another is a flaky coarse-grained ash, like that of felsite, but of a darker green or olive colour. This sometimes contains embedded crystals of hornblende\(^1\) that have had their edges rounded and worn, together with angular or rounded fragments of other rocks.

Another variety of greenstone ash is a dark hornblende slate, passing into hornblende schist; and it is very possible that many hornblende schists, actinolite schists, &c. are metamorphosed ash-beds.

It is obvious that rocks thus made chiefly or entirely of igneous materials would more easily be metamorphosed than purely siliceous, argillaceous, or calcareous rocks, and would then be converted into rocks having all the appearance of trap. If they contained crystals of feldspar or hornblende, such altered rocks could not be separated from porphyries.

Greenstone ash often effervesces with acids as well as felsite ash.

III.—THE GRANITIC ROCKS.

We have before said that all igneous rocks were composed of silicates, and pointed out that the varieties of the volcanic and trappean rocks were characterized by the relative amounts of hornblende or augitic minerals (silicates of magnesia, &c.) which were mingled with their feldspathic constituents (silicates of alumina, &c.). These silicates are, in the volcanic and trappean rocks, generally one of the more basic varieties. The bases, then, in the compound, just previous to consolidation, must have been in comparatively great proportion to the acid (silica), so that none of the latter was left unused or uncombined, and consequently none was allowed to crystallize out separately as quartz. The granitic rocks, on the other hand, are distinguished by the relative abundance of silica which they contain. Not only are all the minerals composing them as highly silicated as possible, but there was moreover a superabundance of silicic acid (or silica) beyond that which could be taken up by the basic substances present in the mass. This silica, therefore, has been left uncombined, and on the cooling and consolidation of the rock was compelled to crystallize out by itself as quartz.

So long as granite was looked upon as necessarily the most ancient of rocks, this superabundance of silica and occurrence of quartz was considered to indicate a difference in the proportion or distribution of the constituents of the globe, in the more ancient geological periods, from that which exists at present. The mineral character of rocks was supposed to depend upon age. We shall touch upon this subject presently.

In the meantime we would observe that we have already seen that some felsites contain distinct crystals of quartz, and pass into quartziferous porphyry. Now, if a rock consisting of granular crystals of quartz and feldspar, in anything like equal proportion, began to contain flakes of chlorite, talc, or mica, it would then pass into a granite; if, instead of a micaceous mineral, it were to acquire any hornblende one, it would then become a syenite.

Again, if a greenstone containing granular crystals of feldspar and hornblende were likewise to exhibit crystals of quartz, it would pass into a syenite; and should the hornblende give way to a mica, this also becomes a granite.

These transitions are not merely hypothetical, but have been observed and described; and we have, therefore, existing in nature, every kind of gradation, from a trachytic or doleritic lava, through a feldspathic or hornblende trap, into genuine granite.

43. Granite.—True granite in its most ordinary form is one of the most easily described and certainly recognized of all rocks. It is a granular, crystalline aggregate of the three minerals feldspar, mica, and quartz. Its name is sometimes said to be derived from its granular structure, but Jameson derives it from "granites," a term used by Pliny to designate a particular kind of stone.

Ordinary granite varies according to the composition of the feldspar, and mica composing it,—according to the relative proportions of those minerals to each other and to the quartz—and according to the size of the crystals and the state of aggregation of the several constituents.

The feldspar of granite may be either orthoclase or potash feldspar, frequently flesh-coloured, but sometimes white; albite or soda feldspar, generally dead white; an intermixture of those two minerals; or lastly, a feldspar containing both potash and soda, which may be called soda-orthoclase or potash-albite, as the case may be. Other varieties of feldspar, except, perhaps in some instances, oligoclase, are seldom found in granite as constituents of the mass.

The mica of granite varies greatly in colour and lustre, being sometimes dark coppery-brown, passing into black; sometimes green, sometimes golden yellow, and sometimes a pure silvery white. Whether its chemical constitution be equally various is perhaps hardly yet sufficiently ascertained. The quartz is commonly colourless or white, but sometimes dark gray or brown.

The proportions of the three constituents vary indefinitely, with this limitation, that the feldspar is always an essential ingredient, and never forms less than a third, rarely less than half of the mass, and generally a still larger proportion.\(^1\) Sometimes the mica, sometimes the quartz, becomes so minute as to be barely perceptible.

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\(^1\) Professor Haughton, in his paper on the Granites of Ireland (Geological Journal, London, vol. xii., p. 180), gives the following as the proportions of the Dublin and Wicklow granite:

| Mica | Feldspar | Quartz | |------|----------|--------| | 13:37 | 61:18 | 24:98 |

A detached granite boss, near Enniscorthy, had

| Mica | Feldspar | Quartz | |------|----------|--------| | 3:60 | 89:69 | 6:44 |

99:73 The state of aggregation of the mass varies also greatly, some granites being very close and fine grained, others largely and coarsely crystalline. The colours of the rock are generally either red, gray, or white; the first when the feldspar is flesh-coloured, the latter when it is pure white, the intermediate gray tints depending chiefly on the abundance and colour of the mica, but sometimes on that of the quartz.

Large and distinct crystals of feldspar sometimes occur, disseminated at intervals through the mass, giving the rock a porphyritic texture. It is then called porphyritic granite.

Other minerals besides the three mentioned above, sometimes occur in granite. Among these are hornblende, actinolite, tourmaline, schorl, chlorite, and steatite.

When hornblende is abundant in rock, and the mica becomes scarce, or altogether disappears, it becomes a syenite.

44. Syenite, in its true form, is a granitic rock. It is named from the city of Syene, in Egypt, where it is formed of a crystalline aggregate of the four minerals feldspar, hornblende, mica, and quartz; the mica being in small and uncertain quantity. We have already, however, had occasion to remark, that syenite may be formed from either felsite or greenstone, and we may look upon it therefore either as a local variety of granite, or as a passage or transition rock between granite and the traps.

45. Protogine.—When talc occurs instead of mica, the granite has been called Protogine, from an erroneous supposition of its being always more ancient than granite.

The name, however, may be retained for the mineralogical variety, independently of any foregone conclusion to be drawn from it.

Instead of talc, chlorite sometimes occurs, as at Camaross, county Wexford, either in regular flakes or as a greenish coating to the surface of other crystals, but I am not aware of any name having been proposed for this variety. The granites of Cornwall and Devon sometimes contain so much schorl as to merit the name of schorl rock, and would doubtless have been christened with two or three different designations by continental geologists.

46. Eurite is a term applied to a fine-grained crystalline aggregate of quartz and feldspar, where the mica is either absent or occurs in such minute flakes as to be invisible.

It generally occurs as veins or as local masses in other granites, and rarely as veins traversing other rocks at a distance from granite. These, therefore, are probably veins of segregation or of injection during consolidation, and not of subsequent formation.

47. Minette is a name for a fine-grained rock, consisting principally of mica, but not having a schistose texture like mica schist.

48. Pegmatite is a crystalline aggregate of quartz and feldspar, in which the crystals are arranged as if with a design to produce a certain pattern, more or less resembling letters or characters (from γραφειν, a coagulation).

49. Granulite is a similar composition, in which the quartz occurs in thin flakes, so as to give almost a schistose texture to the mass.

50. Elvan or Elvanite.—Elvan is a Cornish term for a crystalline granular mixture of quartz and feldspar, forming veins that are either seen to proceed from granite, or occur in its neighbourhood, and may thus be readily supposed to proceed from it.

In the Newry and Mourne mountain district he found three granites having the following proportions:

| | Wellington Inn | S. of Newry | Carlingford | |----------------|---------------|-------------|------------| | Mica | 14-59 | 13-67 | 22-86 | | Feldspar | 61-98 | 64-17 | 50-76 | | Quartz | 23-23 | 21-95 | 26-08 |

It has three varieties:

(a) An equably crystalline mixture of quartz and feldspar; generally fine-grained. This may either be considered as a granite destitute of mica, or as a granular felsite.

(b) A compact felsite base with dispersed crystals, or crystalline particles of quartz, sometimes angular, sometimes rounded, and amygdaloidal. This may be considered as a quartziferous felsite porphyry.

(c) A crystalline granular base of quartz and feldspar, with dispersed crystals of either quartz or feldspar.

The feldspathic portion of these rocks is often earthy, probably from decomposition.

We would propose Elvanite as a good euphonious term, and as being less cumbersome than the term of Quartziferous porphyry, for these rocks which differ in texture from Earite, or Pegmatite, or Granulite.

Professor Haughton, in his paper in the Geological Journal before quoted, gives the following as the composition of some rocks, which we should consider Elvanites.

| Croghan Kinshela, Wicklow | Moorme Mountains | |---------------------------|------------------| | Albite | 62 | | Orthoclase | 44-2 | | Quartz | 28-0 | | | 100 |

The composition of the Carnsore granite is similar, being—

| Felspar | 78-5 | | Quartz | 21-5 | | | 100 |

But this, by its texture and coarsely crystalline grain, deserves to be considered as a true granite; and it moreover does contain occasionally a small proportion of mica.

As the granite rocks are all hypogenous or nether-formed, that is, have all been consolidated before reaching the surface of the earth, they are necessarily devoid of "ash," or of any mechanically-derived accompaniments whatever.

We have remarked above, that the relative quantity of silica had a marked effect upon the nature of the rock; that among the lavas, quartz only appeared in these trachyte porphyries which were beginning to resemble granite; and that among the traps it only appeared among those feldspar porphyries which were closely allied to, and passing into, granite, while from the true granites it is never absent. It has been attempted from this to prove that the more siliceous an igneous rock was, the more ancient it must be. Even Abich says that we may, perhaps, thus deduce a scale for the history of the formation of the earth—those rocks which contain, as essential constituents, "trisilicates" of both their protoxide and peroxide bases, being "primitive," while those which contain quartz are called "primitive Plutonic;" and those without quartz, "primitive volcanic."

M. Riviere also supposes orthoclase to be confined to the older, labradorite to the more recent rocks. The other bases, too, as magnesia and lime, have been supposed to characterise newer rocks than those of soda and potash, and soda itself to be newer than potash.

We would venture to suggest that these mineralogical differences depend upon space or locality rather than upon time; that the proportionate quantity of silica is referable to the depth at which an igneous rock has been cooled or consolidated, or to the nature of those it penetrated, rather than to the time at which it was formed. At great depths in the earth, pure silica itself may possibly be fused by the intense heat there to be met with; and the most refractory silicates may be equally molten at a somewhat less depth, and consolidate or crystallize on becoming cooler a little higher; while those portions of molten matter containing a greater quantity or variety of bases which act as more perfect fluxes may be kept fluid till they reach the surface, and thus consolidate only in the air or in the water.

Whether the whole quantity and variety of the more fusible bases formed part of the original deepest-seated molten mass, and were separated from it on the first cooling and crystallization of the simpler minerals, or whether a larger proportion of those bases was acquired during the passage of the molten rock through the higher part of the earth's crust, and thus the quantity of "flux" increased in proportion as the heat and pressure diminished, may be matter for speculation. We will not now stop to consider it farther than to warn the student not to take it for granted that the mineralogical and lithological composition or structure of any rock whatever has any necessary and determinate relation to its geological age. Granite might become solid at a temperature that would keep felsite or trachyte still fluid; and these might solidify at temperatures which would keep molten all greenstones, basalts, and dolerites, so that from the very same stream of igneous matter proceeding from the interior to the surface of the earth, the more readily fusible portions might be successively squeezed out, as it were, as the infusible ones solidified, and contracted in consequence of that solidification. This action might take place in spite of the greater specific gravity of the more fusible minerals, since the difference in the specific gravities would probably be small compared with the power of the eruptive force.

It is true, indeed, that actual subaerial volcanoes, with cones and craters and conduits, or streams of lava, are only known as recent geological phenomena—as either now active or as having been so during a recent geological period. But we shall see hereafter reason to believe that the preservation of any volcanic cones belonging to the more ancient periods was not to be expected. The parts preserved from destruction and denudation are the more deeply-seated portions only, the roots, as it were, of the volcano, the very parts which we do not see while the volcano is active or entire, but which we do see in some (such as those of the Mont Dore) that are half ruined, and we then find these old lava roots to be essentially the same as the traps; and we have already seen that deeply-formed trap is not to be separated by any hard line from granite. If, therefore, we could follow any actual lava-stream to its source in the bowels of the earth, we should in all probability be able to mark in its course every gradation, from cinder or pumice to actual granite.

That this change of state from a granite into a trappean rock does actually occur is well known, and has been proved in a most interesting manner in Professor Haughton's paper before quoted. Near Carlingford (Ireland), a syenite, having the following composition:

- Hornblende: 15.4% - Orthoclase: 67.18% - Quartz: 17.16%

29.74

comes in contact with, and sends veins into, a large district of limestone. The dykes proceeding from this syenite are converted into a kind of greenstone or dolerite by taking up a large quantity of lime from the adjacent limestone, which enters into combination with the silica, and lets the potash go free, so that their mineral composition becomes,

- Hornblende: 14.16% - Anorthite: 85.84%

100.00

Anorthite, or a lime felspar, is thus formed by the combination of lime with the silica existing in the mass, which in parts not reached by the lime can only form orthoclase and quartz. Anorthite had not been previously mentioned as a constituent of any other rock than a lava, and yet we see it here occurring in a mass proceeding from a granitic syenite, and therefore we may well suppose lava in many cases to have similarly proceeded from a granitic compound.

M. Delesse, in the Annales des Mines, 1849, has some interesting observations on the magnetic power of the geology, igneous rocks, and some of their constituent minerals, as also of some of the glasses formed from melting rocks. No practical results, however, being yet arrived at, we shall confine ourselves to this mention of the subject. (D'Archiac, vol. iii., p. 595.)

Bischof has some very important observations on the contraction of igneous rocks, as they pass from a fluid to a solid or crystalline state. (D'Archiac, p. 598.)

He experimented on basalt, trachyte, and granite, and found the following results:

| Volume in the state of Glass | In Crystalline state | |-----------------------------|---------------------| | Basalt | 1 | | Trachyte | 1 | | Granite | 1 |

| In the Field state | In Crystalline state | |-----------------------------|---------------------| | Basalt | 1 | | Trachyte | 1 | | Granite | 1 |

From this we see that granite contracts 25 per cent., or a quarter of its volume, in passing from a fluid to a crystalline state, and 16 per cent. in passing from a glassy to a crystalline state. These effects must have had a great importance "when the primary granites were first cooling," says M. D'Archiac; but their importance seems to us still greater to geologists who are examining the broken and contorted rocks on the flanks of existing granite chains, and the phenomena of intrusion which we shall hereafter meet with in such situations. M. Deville and M. Delesse arrive at results rather different from Bischof's, and the latter gives the following table as comprising the limits within which the several rocks mentioned contract on passing from a fluid to a solid state.

Granite, leptynite, quartziferous porphyries, &c. 9 to 10 per cent. Syenite granite, and syenite ......................... 8 to 9 Porphyry, red, brown, or green, with or without quartz, having a base of orthose, oligoclase, or andesite ........................................... 8 to 10 Diorites and porphyritic diorites (greenstones) .... 6 to 8 Melaphyres .............................................. 5 to 7 Basalts and trachytes (old volcanic rocks) .......... 3 to 5 Lavas (volcanic and vitreous rocks) ................. 0 to 4

M. Delesse sums up his results as follows:

"When rocks pass from a crystalline to a glassy state, they suffer a diminution of density which, all things being equal, appears to be greater in proportion to the quantity of silica and alkali, and, on the contrary, less in proportion to that of iron, lime, and alumina which they contain. In arranging the rocks in the order of their diminution of density, those which we regard as the more ancient are generally among the first, while the more modern are the latter; and in each case their order of diminution of density is almost exactly the inverse of their order of fusibility."

On this we would remark as before, that for "ancient" and "modern" might be substituted "deeply formed" and "superficially formed;" the most infusible and the most contractible rocks being those produced at the greatest depth and under the greatest pressure, while the highly fusible compounds escape to the surface, and suffer little contraction or solidification.

M. D'Archiac remarks, that if granite contracts on cooling only ten per cent., and that there be a thickness of 40,000 metres of it in the crust of the globe, crystallization alone would diminish the terrestrial radius at least 1430 metres, and consequently alter the form and rapidity of ro-

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1 The chemist is reminded of the fact, that if a mixture of metals, as for instance tin, bismuth, and lead, be melted, they will, as the mixture cools, have a tendency to solidify and crystallize separately as the temperature of the mass reaches their respective melting-points. This constitutes a great difficulty in large bronze castings.

2 We would just warn the student here, that, without altogether denying that there may have been such a rock as a primitive granite, none of the granites now known at the surface can be shown to have an antiquity greater than that of some of the aqueous rocks with which they are associated. tation of the earth. Such speculations are practically useless only in a negative sense, as showing the great improbability of anything like a shell of 40,000 metres having cooled and consolidated at once in the crust of the earth during any of the known geological epochs.

**CHAP. III.—AQUEOUS ROCKS.**

We are compelled to look upon the purely igneous rocks as original productions. We can only speculate, and that very vaguely, on what was the condition of the materials which compose them, previously to their being placed, in a molten state, in the positions where they subsequently consolidated.

In our examination of the aqueous rocks, however, we can go a step farther back, and learn, either accurately or approximately, whence the materials composing them were derived, and what was their previous condition. This is true of all aqueous rocks, whether chemically, organically, or mechanically formed.

We will examine the mechanically-formed rocks first.

1.—MECHANICALLY-FORMED ROCKS.

**Preliminary Remarks on their Origin.**

The instruments used by nature in the production of these rocks are,—moving water, whether fluid or solid (ice), and moving air.

**The Sea.**—The sea is probably never and nowhere stagnant. Currents, moving with greater or less rapidity, keep the whole mass in circulation; so that we may look upon the ocean, through all its depths, and in all its gulfs, bays, and recesses, as one great slowly moving whirlpool.

It is probable, however, that no currents produce any marked or appreciable effects upon solid rock at great depths of water. The mechanical powers of the sea are principally brought into action by the motion of its surface along the shores of all lands, and in its narrower and shallower channels. Sea-breakers along beaches, and at the foot of cliffs, act like ever-moving jaws constantly gnawing at the land. The currents caused by the ebb and flow of the tides along shallow shores remove some of the eroded materials; the great oceanic currents of circulation, where they strike upon coasts, carry off others, and transport all, either immediately or immediately, to greater distances.

In looking at the destructive action of water, however, we must never forget that by destruction we do not mean annihilation, but only re-arrangement. Rock forming "land," that is, rock above the level of the sea, is destroyed; but its materials are carried off and deposited, either in similar or in different combinations, to form rock below the level of the sea.

For instances of the erosive and destructive action of the breakers, and the abrading and transporting power of currents, during historic times, we must refer the student to Sir C. Lyell's *Principles of Geology*, chapters 20, 21.

**Rain.**—The sea, however, is not the sole agent of the destruction of that portion of rock at or above its level, which we call land. All rain falling upon land, and either running over its surface or draining through its interior, is constantly abrading and carrying off particles of pre-existing rock in the shape of mud, silt, and sand. From the gutters and the ditches, from the rills, the streams, and the brooks, these materials for the building of mechanically-formed rocks are almost unceasingly being carried into the rivers, and by them transported to the beds of lakes and seas. Rain soaking into ground, and issuing as springs on steep slopes or precipices, sometimes exerts a more wholesale destructive power, by gradually loosening and undermining very considerable masses of ground, and thus causing them to be launched forward, down the slope, producing what are called "landslides."

**Ice and Snow.**—When rain falls as snow, on the other hand, it exerts a conservative and protective effect as long as it retains its solid form, but, on melting, acts like rain, and even with greater intensity, insomuch as a greater amount of water is often set loose and in motion over the land by the rapid melting of snow than would fall in the same space of time in the shape of rain directly from the clouds. The most extensive and powerful floods are those of the spring in mountainous districts, when the snows melt rapidly on the hills. If rain or other water soaks into rocks and fills up their interstices, either the small pores, or the crevices, joints, and fissures by which all rocks are traversed, and this water then freezes, this conversion into ice is accompanied by an expansion which exercises an almost irresistible mechanical force, the effect of which will be either the disintegration of the particles in the one case, or the breaking and rending asunder, and the displacement of the larger masses in the other. On mountain summits and sides subject to great vicissitudes of temperature, this agency exerts no mean effect. The hardest rocks will be broken up by it, and enormous blocks ultimately displaced and toppled over precipices, or set rolling down slopes to suffer still further fracture, and produce still greater ruin in their fall.

**Glaciers.**—When mountains are covered by perpetual snow, all the part so covered is protected by this envelope from all change. In such situations, however, the moving power of water takes another form, that of the glacier, or "river of ice." The lower border of the perpetual snow-mass passes into ice, from the alternation of melting and freezing temperatures, just as snow on the roof of a house forms icicles at its lower edge, when partly melted and refrozen. This ice accumulates in the valleys, and is frozen into a solid or nearly solid mass, called a glacier. Glaciers sometimes fill up a valley 20 miles long, by 3 or 4 wide, to the depth of 600 feet. Although apparently solid and stationary, they really move slowly down the valley, and carry with them, either on the surface, frozen into their mass, or grinding and rubbing along the bottom, all the fragments, large and small, from blocks many tons in weight, down to the finest sand and mud, that rain, and ice, and the friction of the moving glacier itself, detach from the adjacent rocks. The cause of this motion is now generally believed to be that attributed to it by Professor J. Forbes, namely, a slight degree of plasticity, a demi-semifluidity, in the ice mass, by which it is enabled to actually flow down the valley, just as a viscous substance, such as partially melted pitch, would flow.

The glaciers of the Alps, and probably those of other parts of the world, descend to a vertical depth of nearly 4000 feet below the line of perpetual snow, before they finally melt away, and leap forth as rivers of running water. The confused pile of materials, of all sorts and sizes, which they there deposit, is called the "moraine." This word is also applied to the lines of blocks that are being carried along on the surface of the glacier. The river of water that proceeds from the end of a glacier is of course quite unable to move the large blocks which had been carried with ease by

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1 See Maury's *Physical Geography of the Sea*, and Johnstone's *Physical Atlas*, &c.

2 Professors Tyndal and Huxley have recently disputed this idea of Professor J. Forbes's, and shown the motion of glaciers to be the result of the minute, almost molecular, fracture and vegetation of the ice particles, which move as if they were sand continually thawing and re-freezing. (*Philosophical Magazine*, 1856.)

3 See Professor J. Forbes's work on the *Glaciers of the Alps*, and also Johnstone's *Physical Atlas*; also the works of Agassiz, Charpentier, &c. that of ice, and only transports the finer particles, as mud and sand.

Icebergs.—If, however, it so happen that a glacier come down into a lake, or into the sea, before it melt away, large fragments of it (icebergs) will be frequently floated off, with all their freight of rock-fragments of all kinds; and these loaded icebergs may then be carried great distances before they entirely dissolve. In this manner, large unworn angular blocks of rock may sometimes be dropped on the bed of the sea even hundreds of miles from their original site. The terminal moraine, instead of a pile at the foot of the glacier, is disseminated far and wide over the bottom of the surrounding seas.

River Valleys.—Rivers are not the producers of their own valleys; they are the results of those valleys, but they are their immediate results. The river could not be formed till after the valley, with all its tributary branches, had been marked out; but the valley could not even be marked out without the river, in most cases, instantly springing into existence, and commencing to modify, and deepen, and complete the valley.

Action of Rivers.—The re-direction of draining water into old channels will be more certain and frequent in proportion to the steepness of the ground and consequent rapidity of the flow of water; and channels once selected will there be more rapidly deepened, and more completely and permanently formed. Such deep valleys (ravines, as we should then call them) are scarcely to be obliterated, or otherwise altered than from deepening and enlargement, by any number or amount of changes, short of the removal of the mass of high ground which they traverse. As long as the mountains remain undestroyed, the valleys and ravines must obviously be continually enlarged, either vertically or laterally, by the action of the waters which traverse them.

The temporary damming up of rivers, and subsequent breaking down of the barrier and escape of the lake formed above it, produces sometimes the most remarkable instances of the power of moving water. Rocks as big as houses are thus set in motion, and carried sometimes for very considerable distances down the valleys. (See Lyell as above; also Jameson's Mineralogy, vol. iii., where all these causes of mechanical destruction, including that of ice and icebergs, are distinctly pointed out.)

We shall be able better to understand how rapidly the size of water-borne fragments increases in proportion to the velocity of the moving water, when we learn from Mr. W. Hopkins, that the power of water to move bodies that are in it increases as the sixth power of the velocity of the current. Thus, if we double the velocity of its current, its motive power is increased sixty-four times; if its velocity be multiplied by 3, its motive power will be increased 729 times; if by 4, 2048 times; and so on.

In studying the mechanical force of water upon rock, also, it is necessary to bear in mind that all earths and stones lose fully a third of their weight when suspended in water. These considerations enable us to understand more readily the fact of blocks of rock many tons in weight having been removed from breakwaters and jetties, and carried sometimes many yards during great storms, as also of still larger blocks hurried along by floods, &c.

The rolling power of water upon stones lying in its bed depends greatly on their shape also, the same current being easily able to roll along pieces of rock in the form of rounded pebbles that it would be quite unable to move if they were in the shape of flat slabs; while, reversely, flat slabs or flakes would float more easily, or sink more slowly, than rounded or square-shaped fragments of the same weight and cubic contents. Flakes of mica, therefore, might be floated and transported onwards where grains of quartz, even though lighter than the micas, would sink; and, on the other hand, rounded quartz pebbles might be rolled forward where smaller and flatter pieces, in the shape of shingle, would be brought to rest.

Mr. Babbage has lately treated of this subject, in a paper of which an abstract appeared in the Journal of the Geological Society, November 1856.

He there supposes the case of a river, the mouth of which is 100 feet deep, delivering four varieties of fine detritus into a sea which has a uniform depth of 1000 feet over a great extent, which sea is traversed by one of the great ocean currents, moving with a certain velocity.

He takes for granted that the four varieties of detritus are such as, from their size, shape, and specific gravity, would fall through still water, the first 10 feet per hour, the second 8 feet, the third 5 feet, and the fourth 4 feet. The combined effect of the downward motion of the detritus, and the onward motion of the water, would then bring the first variety to the bottom of the sea, at a distance of 180 miles from the river's mouth, and strew it over a space 20 miles long; the second variety would only begin to reach the bottom 225 miles from the river's mouth, and would be spread over 25 miles, and so on, as in the following table:

| No. | Velocity of fall per hour | Nearest distance of deposit to river mouth | Length of deposit | Greatest distance of deposit from river mouth | |-----|--------------------------|------------------------------------------|------------------|---------------------------------------------| | | Feet. | Miles | Miles | Miles | | 1 | 10 | 180 | 20 | 200 | | 2 | 8 | 225 | 25 | 250 | | 3 | 5 | 360 | 40 | 400 | | 4 | 4 | 450 | 50 | 500 |

We should thus have, proceeding from the same river, and poured into the sea, either simultaneously or at different times, four different and widely separated patches of mud or clay formed on the sea bottom.

Mr. Babbage says, that this subject was suggested to him from his observing the extreme slowness with which a very fine powder, even of a very heavy substance, such as emery, subsides in water, and speaks of mud clouds being suspended in the depths of the ocean, where the density of the water increases, for vast periods of time.

The amount of mechanical work done by rivers can be estimated by examining their waters at different periods, and determining their solid contents. If this be done by simply evaporating the water, the result will be not only the mechanically suspended mineral matter, but also that which was chemically dissolved in the water. As the separation of these two, however, is rather troublesome, and not very important, it is not often attempted; neither, as a measure of the work done, would it be often necessary, since the chemical solution of mineral matter is perhaps more frequently than not the consequence of the mechanical erosion of it by the water.

Sir C. Lyell, in his Principles, gives the following as the results of various observations:

The total mineral matter carried down by the Ganges into the sea, according to Everest, is 6,368,077,440 cubic feet per annum, part of which has been deposited at its mouth, forming a gentle submarine inclined plane of 100 miles long, and sloping from 4 fathoms to 60 fathoms in depth. Lyell says, that for the transport of this quantity, it would require a fleet of 2000 Indiamen, each of 1400 tons, to start every day throughout the year. This mass of matter would cover a square space 15 miles in the side every year with mud a foot deep, or would raise the whole surface of Ireland 1 foot in the space of 144 years. The Brahmapootra probably carries an equal quantity.

Mr. Barrow calculated that the Yellow River (Hoang Ho) in China, carried down into the Yellow Sea 48,000,000 of cubic feet of earth daily; so that, assuming the Yellow Sea to be 120 feet deep, an English square mile might be converted into dry land every seventy days, and supposing its area to be 123,000 square miles, the whole would be made into terra firma in 4,000 years.

Herodotus remarked that "Egypt was the gift of the Nile," and that the sea probably once flowed up to Memphis, the old gulf having been filled up by the Nile mud, as the Red Sea would be filled up if the Nile were turned into it. The edge of the present delta is, however, now swept by a powerful current, which carries off all detritus delivered into it, and thus future increase is

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1 The supposed velocity of the river and ocean current is not stated in the abstract. prevented. Otherwise the Nile would by this time have formed a long tongue of land projecting into the Mediterranean, just as the Mississippi has projected a tongue of land 50 or 80 miles long, into the Gulf of Mexico, having previously filled up the inlet which formerly penetrated from that sea deeply into North America, and received the rivers more than 100 miles inland from the present coast.

According to Dr. Hildebrandt, the solid matter contained in the Mississippi is about 20 parts in the 100,000 of water by weight, or about 33 by volume; and Sir C. Lyell calculates, that it brings down 3,792,758,400 cubic feet annually, so that the present delta has required 67,000 years for its formation.

If we turn to the European rivers, Bischof states that Chandelier, by daily experiments during December 1849, found in the Maas, at Leige, a maximum of 47-4 parts of suspended matter alone, a minimum of 1/4, and a mean of 10 parts, in the 100,000 of water.

In the Rhine, at Bonn, Mr Leonard Horner found, August 1833, when it was unusually low and turbid, 31-02 of suspended and dissolved matter; and in November, when swollen, 51-45. Bischof found in March 1861, 20-5 of suspended matter alone; and at another time, when it was clear, only 1-73 of such parts; while Steffens, near Uerdingen, after a flood, found 78 parts of suspended matter in the 100,000 of water.

In the Danube, August 5, 1852, there were found 9-23 of suspended, and 11-14 of dissolved matter—total solids, 23-37 in the 100,000; while in the Elbe at Hamburg, there were in June 1852 only found 0-9 of suspended, and 12-7 of dissolved matter.

In these experiments much depends on the state of the river, and also on the part of the river where the water is taken from, whether far from the bank, at the surface, or near the bottom; and so on.

Whether the matter thus carried down by rivers is deposited at their mouths, and forms a delta, or is carried off to a greater or less distance, depends on the tidal or oceanic currents which are to be met with at the mouth of the river. In lakes, deltas or flats are almost invariably met with at the mouths of rivers. In sheltered bays and gulfs, where there is no great rise and fall of tide, and consequently no great scour of the river's mouth, deltas are also formed; witness the Po, the Rhone, Nile, Mississippi, Orinoco, Indus, Ganges, Brahmapootra, &c. Where, however, there are strong ebb tides, or where the river mouth is swept by a strong oceanic current, the detritus is carried off directly into the sea, as in the case of the Amazon, the Rio de la Plata, the St Lawrence, and of most of the rivers of Britain and Western Europe.

It results from even such a hasty and rapid glance as we have just thrown over the principal mechanical powers of moving water that are daily and hourly at work around us, that we begin to acquire the notion that we are living in a vast workshop, and that all the earthly matters we see about us, the mud, the clay, the soil, the dust, the sand, the gravel, and the boulders, are only so much raw material in process of manipulation. They may be likened to the refuse and chips of some vast manufactory. They are the building materials of stratified rocks, which are being carried from the quarry to the place of construction, much being dropped and scattered by the way. Every pebble, every grain of sand, every atom of mud, is a fragment of pre-existing rock, removed at some period of past time, and destined ultimately to enter into the structure of some other rock in the future.

This building metaphor might be carried still further when we come to speak of the chemically-formed rocks, since many of the mechanical deposits are bound together by cements and mortars which are more or less identical in composition with those used in architecture.

**Description of Mechanically-Formed Rocks.**

51. Conglomerate, Puddingstone, Breccia.—In the preceding paragraphs, we have mentioned the method of formation of pebbles, gravel, and shingle, in rivers and along the sea-coasts. When those materials are compacted together into stone, they are called conglomerate or puddingstone if the pebbles are round, breccia if the fragments are sharp and angular.

The degree of induration or consolidation in conglomerates varies greatly. Some seem to have been consolidated by simple pressure; and from these the pebbles may often be removed by a slight blow with the hammer, or even by the knife, the form or mould of the pebble remaining in the little film of sand which fills up all the interstices between the larger fragments. Sometimes the conglomerate has been bound or cemented together by calcareous, ferruginous, or siliceous infiltrations, the matrix in which the pebbles lie being as hard and indestructible as the pebbles themselves; a blow with a hammer breaking the pebbles as easily as the mass of the rock in which they are embedded. The size of the fragments in conglomerates and breccias varies greatly. In some rarer cases, blocks of as much as two feet in diameter occur; but the more ordinary sizes are from that of a man's head to that of walnuts. Below that size, the rock begins to pass into the coarser varieties of sandstone.

52. Sandstone and Gritstone.—The very process by which fragments of rock are rounded produces sand, as the waste resulting from their attrition. Pebbles themselves also are gradually broken or diminished into grains of sand. Sandstone is nothing else but sand, formerly loose and incoherent, subsequently compacted into solid stone. The grains both of sand and sandstone generally consist of quartz, sometimes clear and colourless, sometimes dull white, sometimes yellow, brown, red, or green. The red colours are usually the result of the covering of each little grain with peroxide of iron, which sometimes acts as a sort of cement to the stone, serving to bind the particles together. The green colours are commonly derived from silicate of iron; and the green and red are often intermingled, in consequence of the change of the iron from the condition of a silicate to that of an oxide or peroxide.

The size of the grains varies from that of a pea to the minutest particle visible to the naked eye; many sandstones and gritstones even requiring a lens in order to distinguish the particles of which they are composed.

The materials are equally various, as, along with grains of quartz, may occur grains and particles of any mineral substance whatever. Grains of feldspar, distinguishable by their dull white colour and peculiar appearance, occur abundantly in some sandstones, which may then be called feldspathic sandstones. Flakes and spangles of mica are rarely altogether absent; and in many sandstones they occur so abundantly, and in such regular seams, as to cause the rock surfaces to glitter, and the rock itself often to split into thin plates and slabs. These are called micaceous sandstones. When grains of limestone occur in any remarkable proportion, the rock may be called a calcareous sandstone, though this designation is often applied to sandstones the quartzose or other grains of which are bound together by a cement of carbonate of lime, either invisible to the eye or occurring as a network of little veins and strings of crystalline carbonate of lime running throughout the stone. Other varieties of sandstone are similarly named from the prominent character of some part of their contents.

Argillaceous sandstone is a term not often used, nor is it very often applicable, though many rocks contain various mixtures of sand and clay. In many sandstones, too, little flat rounded patches of clay, more or less indurated, often occur. Similar little patches of clay may be seen on sandy shores, either originally deposited there in little hollows, or rolled as clay pebbles from some bed of clay. In quarrying sandstone, these clay patches are commonly called "galls" by the workmen. In highly indurated grits, they sometimes assume the form of pebbles of slate, though the slaty structure may often have been assumed in consequence of the subsequent induration, and not before they were embedded in the sandstone. There are many local terms used by quarrymen and miners for different varieties of sandstones, such as—

Rock, used generally in South Staffordshire to denote any hard sandstone.

Rotted or rotten rock, is generally used for a softer and more friable stone.

Rubble, means either loose angular gravel, or a slightly compacted brecciated sandstone.

Hard is a North of England term for a hard grit.

Post is a similar term for any bed of firm rock, and is generally applied to sandstone.

Peldon is a South Staffordshire term for a hard, smooth, flinty grit.

Colliford, or galliford, is a northern term for a similar rock.

Freestone is a term in general use, which is often applied to sandstone, but sometimes to limestones, and even to granite, as in the counties of Dublin and Wicklow. It means any stone which works equally freely in every direction, or has no tendency to split in one direction more than another.

Flagstones, on the contrary, means a stone which splits more freely in one direction than any other, that direction being along the original lines of deposition of the rock. These stones are ordinarily sandstones, though often very argillaceous, and some flagstones are perhaps rather indurated clay in thin beds than sandstone. Thin-bedded limestones may likewise often be called flagstone.

Sandstones, like conglomerates, may have been consolidated either by simple pressure continued for a long period of time, by pressure combined with an elevation of temperature, by the infiltration of mineral matter in solution, or by the aqueous or igneous solution and subsequent reconsolidation of some of the particles composing it; or lastly, by a combination of two or more of these actions. Some of the loose tertiary sands of the North of France, such as the Sable de Fontainebleau, and the Sable de Beauchamp, exhibit these actions in a very remarkable way. The Sable de Fontainebleau is a pure white siliceous sand. It is covered in some places by beds of a freshwater limestone called the Calcaire de Beauce. Water containing carbonate of lime in solution, derived either from this limestone, or from other sources, percolates through the sand, and deposits the lime, binding the sand either into globular concretions, or even into rhombohedral crystals, such as carbonate of lime ordinarily forms.

Besides these smaller concretions, other large parts of the sand have been cemented together, either at the time of deposition, or subsequently, into a very hard white gritstone, which is extensively used as a paving-stone in the district where it occurs. This grès de Fontainebleau forms picturesque crags and precipices, all the more striking perhaps, from the loose and easily removed sand in which the beds and other irregularly formed masses of the consolidated rock occur. The cementing substance of the sandstone may in some cases be carbonate of lime, equally diffused through the mass. In other cases, however, the quartzose grains appear to be bound together by a siliceous cement, as if the percolating water had contained dissolved silica. This is obviously the case in one variety, a glittering rock being produced, greatly resembling ordinary quartzite, only more white and lustrous; this variety is called "grès lustrés," or lustrous grit.

The grès de Beauchamp consists of similar locally consolidated and semi-concretionary lumps of sandstone, occurring here and there in loose sand. On the plains north of Maulne, these lumps of gritstone are discovered by ploughing or plowing the loose sands with an iron rod, and they are then extracted and broken into square blocks, and used for forming the roads of the country. These tertiary grits are often as hard and intractable, and break with as splintery a fracture under the hammer of the geologist, as the grits he is accustomed to meet with among the oldest rocks of the British mountains.

When among the materials of a sandstone there occur any containing a notable proportion of alumina, which may be known by the earthy odour given out when the rock is breathed upon, we have the constituents for the formation of clay, and it only remains for those materials to be ground down into fine powder and mixed with water, either naturally or artificially, for clay to be produced.

53. Clay.—Perfectly pure clay is a hydrated silicate of alumina. This is the substance known as "kaolin," or "porcelain clay," derived from the decomposition of orthoclase, albite, or other feldspars, from which the silicates of potash, soda, &c., have been washed out. In some granitic districts, the granite being decomposed yields this substance, which is carried down by water, and deposited in hollows, the quartz and mica being often left behind in the state of loose sand.

Common clay, however, is often largely coloured with oxide of iron, and mingled with many impurities, besides being mixed in variable proportions with sand. Any very finely divided mineral matter, which contains from ten to thirty per cent. of alumina, and is consequently "plastic," or capable of retaining its shape on being moulded and pressed, would commonly be called clay.

These clays have a number of varieties, of which the following are the principal:—

Pipe-clay, free from iron, white, nearly pure.

Fire clay, nearly free from iron, and free from all alkalies, often containing carbon, but this does not prevent its forming bricks that will stand the heat of a furnace.

Shale, regularly laminated clay, more or less indurated, and splitting into thin layers along the original laminae or planes of deposition of the rock. The colliers' and quarrymen's terms for shale are Band, or Blueband, Metal, Plate, &c. When very fine, and containing a large proportion of carbonaceous matter, the collier calls it Band or Bas, the geologist carbonaceous or (bituminous) shale, and the coal merchant often "slate." In Scotland the collier's term for shale appears to be "blues," or "blues," the shales being often bluish gray. When lumpy, they are called "lumpy blues." Black, argillaceous shales (or batis) are called "danks;" "fekes," or "gray fakes," seem to be sandy shales such as would be called "rock binds" in South Staffordshire. (See William's Mineral Kingdom.) In the South of Ireland carbonaceous shale is called "kelly," and indurated slaty shale is termed "pinnish," or "pencil," as it is used often for slate pencils.

Claystone is a common name for a tough, more or less indurated clay, often calcareous.

Loam is a soft and friable mixture of clay and sand, enough of the latter being present for the mass to be permeable by water, and to have no plasticity.

Marl is properly calcareous clay, which, when dry, naturally breaks into small cubical or dice-like fragments. Many clays, however, are commonly but erroneously called marls, which do not contain lime.

Argillaceous flagstone is an indurated sandy clay or clayey sandstone, which splits naturally into thick slabs or flags.

Clay slate is a metamorphosed clay, differing from shale in having a superinduced tendency to split into thin plates, which may or may not coincide with the original lamination of the rock. It will be more particularly described among the metamorphic rocks.

II.—CHEMICAL AND ORGANIC ROCKS.

Preliminary Observations on their Origin.

Before entering on the description of these rocks, it will be useful briefly to consider the nature and action of the forces concerned in their production. We shall take as our principal guide in this examination Bischof's Chemical and Physical Geology, as translated for and published by the Cavendish Society.

Carbonate of Lime.—Carbonate of lime is nearly insoluble in pure water, but if the water contain carbonic acid gas, the mineral is easily dissolved by it, either in consequence of some special solvent power in water so impregnated, or in consequence of the carbonate being converted into a soluble salt (never yet seen in a solid state) in the form of a bicarbonate of lime.

Rain water and snow contain small quantities of carbonic acid derived from the atmosphere, and acquire more in sinking through the soil.

If water, in sinking into the earth, meets with carbonic acid gas rising from the interior, it becomes saturated with it, and

1 This term of "bat"—commonly applied in South Staffordshire to a lump of shaly coal which will not continue to burn in the fire, and therefore soon becomes ash, and is consequently of little worth—has gone out of general use in the English language except in composition, where it is retained in the word "brick-bat" for the broken end of a brick. carbonated springs are produced. The waters of springs, rivers, and lakes, therefore, always contain some, and probably a very variable amount of carbonic acid gas. The waters of the European seas, according to Vogel and Bischof, contain from 7 to 23 parts by weight of carbonic acid gas in the 100,000 of water. But from experiments made in the French ship "Bonite," in the Indian Ocean, only from 0.4 to 3.0 parts by weight in the 100,000. (Bischof, vol. i., p. 113, &c.)

The quantity of carbonate of lime thus held in solution by water containing carbonic acid gas is likewise very variable. In springs it may occasionally reach the point of saturation, which is about 105 parts in the 100,000.

In the rivers of Great Britain and Western Europe, the quantity of mineral matter held in solution varies from 4 to 55 parts in 100,000 parts of water, the mean quantity being 22. Of this mineral matter one half is commonly carbonate of lime, the least proportion, or 35 per cent., being found in the Loire; the greatest, 82 to 94 per cent., in the Rhone at Lyons. The quantity of mineral matter in the Thames, near London, is 33 in the 100,000 parts of water, 15 of which, or 46 per cent., are carbonate of lime. Bischof calculates that if the mean quantity of carbonate of lime in the Rhone be assumed as 9.46 in the 100,000 of water, which it is at Bonn, then, according to the quantity of water estimated by Hagen to flow at Emmerich, enough carbonate of lime is carried into the sea by the Rhine, for the yearly formation of three hundred and thirty-two thousand millions of oyster shells of the usual size.

Notwithstanding the vast quantity of carbonate of lime thus carried down into the sea, observation shows that the quantity to be found in sea-water is commonly very small. In most analyses of sea-water it is not mentioned at all. Sea-water from Carlisle Bay, Barbadoes, contained 10 parts in 100,000; sea-water from between England and Belgium, only 5.7 parts in 100,000. In the open sea, at a distance from any land, it is said to be rarely if ever discoverable by analysis.

The smallness of the quantity to be found in sea-water, compared with that in almost all rivers, is doubtless owing to the quantity of carbonate of lime constantly abstracted from sea-water by marine animals, in order to form their shells and other hard parts.

Bischof states that the quantity of free carbonic acid gas contained in the sea, is five times as much as is necessary to keep in a fluid state the quantity of carbonate of lime to be found in it. He argues, therefore, that it is impossible for any carbonate of lime to be precipitated in a solid form at the bottom of the sea by chemical action alone.

Carbonate of lime is deposited on land by springs and rivers, in consequence of the evaporation of the water, and the consequent extrication of a portion of the carbonic acid gas that previously held the carbonate of lime in solution.

But it is clearly impossible for any evaporation of water and gas to occur to a sufficient extent in the sea for this precipitation to take place. We are almost compelled, therefore, to conclude with Bischof, that all our marine limestones have been formed by the intervention of the powers of organic life, separating the little particles of carbonate of lime from the water and solidifying them, in order to enable them to form part of a solid rock.

There is of course the possibility that the sea once contained a much greater proportion of carbonate of lime than it does now, though this does not appear likely when we recollect that in the earliest and least fossiliferous of our formations there is a much smaller proportion of limestone than in later and more fossiliferous rocks; and that even in the oldest limestones organic remains are to be found.

The purely chemical processes now open to our observation, in which limestone is being formed, are the following:

54. Stalactites and Stalagmites, Travertine and Calc Sinter, are formed in places where water containing carbonate of lime in solution suffers from evaporation, and deposits the carbonate in a solid form. Each drop of water loses by evaporation both water and carbonic acid gas, thus becoming more saturated with the carbonate of lime, at the same time that it loses some of its solvent power. It is therefore forced to part with some of this carbonate of lime, which adheres in a solid form to the nearest part of the solid substance over which the water passes. In the case of stalactite and stalagmite, a coating of solid matter is thus formed, with long icicle-like pendants hanging from the roof of caverns or arches, and columns rising from the floor wherever the water continues to drop long enough in one particular spot. Vertical sheets of it may even be formed when the water oozes from a long joint or crevice in the roof. The part hanging from the roof is called stalactite; that on the floor stalagmite. The limestone thus formed is commonly white or pale yellow, subcrystalline, often fibrous, and when thin, semitransparent or translucent.

Stalactites may often be seen under the arches of bridges, vaults, or aqueducts, especially if the stone of which they are built be limestone. Sometimes they are even derived from the carbonate of lime contained in the mortar or cement used in their construction.

Travertine, or Calcareous Tufa, is deposited by exactly the same process on the margins of springs or on the banks of rivers and the sides of waterfalls, or wherever water containing carbonate of lime in solution is brought into circumstances where rapid evaporation can take place. Sticks and twigs hanging over brooks often become coated with it; and the incrustation of bird's nests, wigs, medallions, and other matters, by the action of what are called petrifying wells, is commonly known. In Italy large masses of solid and beautiful travertine are deposited by some of the springs, so that it is used as a building stone. The Colossus at Rome is built of stone thus formed. The name travertine is derived from the Tiber, meaning simply Tiber-stone.

Pipes to convey water, especially water from boilers, frequently become choked up by the deposition of limestone. Bischof says that there are fifty springs near Carlisle giving out 800,000 cubic feet of water in twenty-four hours, from which, according to Walchner's calculation, a mass of stone weighing 200,000 pounds could be deposited in that time.

Marine Limestones.—The marine depositions of carbonate of lime now taking place are best studied in coral reefs. In almost all tropical seas, incrusting patches or small banks of living coral are to be found along the shores, wherever they consist of hard rock, and the water is quite clear. In the Indian and Pacific Oceans, however, far away from any land, huge masses of coral rock rise up from vast and often unknown depths just to the level of low water. These masses are often unbroken for many miles in length and breadth; and groups of such masses, separated by small intervals, occur over spaces sometimes of 400 or 500 miles long, by 50 or 60 in width. The barrier-reef along the N.E. coast of Australia is composed of a chain of such masses, and is more than 1000 miles long, from 10 to 90 miles in width, and rises at its seaward edge from depths which in some places certainly exceed 1800 feet. These reef masses consist of living corals only at their upper and outer surface; all the interior is composed of dead corals and shells, either whole or in fragments, and the calcareous portions of other marine animals. The interstices of the mass are filled up and compacted together by calcareous once contained them. Organic forms have, however, lately been discovered in altered limestone from the gneiss of Scotland. sand and mud, derived from the waste and debris, the wear and tear of the corals and shells, and by countless myriads of minute organisms, mostly calcareous also. The surface of a reef, where exposed at low water, is composed of solid-looking stone, which is often capable of being split up and lifted in slabs, bearing no small resemblance to some of our oldest limestones. These slabs and blocks, when broken open, are frequently found to have a semicrystalline structure internally, by which the forms and the organic structure of the corals and shells are more or less disguised and obliterated. The "bottom" in and among the reefs composing the great Australian barrier, at a depth of some twenty fathoms, often looked, when brought up in the dredge, very like the unconsolidated mass of some of the coarse shelly limestones to be found among the oolites of Gloucestershire. At other times the dredge came up completely filled with the small round foraminiferous shells called orbitolites, and these organisms seemed in some places to make up the whole sand of the beach either of the coral islets or of the neighbouring shores. In the deep sea around, and in all the neighbouring seas, from Torres Straits to the Straits of Malacca, wherever "bottom" was brought up by the lead, it was found to be a very fine-grained impalpable pale olive-green mud, which was wholly soluble in dilute hydrochloric acid. This substance, when dried, would therefore be scarcely different from chalk, though it commonly was of a greener tinge. Raised coral reefs, in the islands of Timor and Java, were often internally as white and friable as chalk, though they had frequently a rougher and grittier texture, and weathered black outside. The weathered surfaces of these limestones, often at a height of 200 or 300 feet above the sea, with their embedded shells of all descriptions, including a tridacna of one or two feet in diameter, differed in no respect from some of the surfaces of the Great Barrier Reef, where exposed at low water.

(Voyage of H.M.S. Fly.)

On the upper surfaces of some of the existing coral reefs small islands are formed; the coral sand being drifted by the winds and waves till it forms a bank reaching above high-water mark. In some of these islands the rounded calcareous grains are bound together into a solid stone by the action of rain-water, which, containing a small quantity of carbonic acid, dissolves some of the carbonate of lime as it falls, but being shortly evaporated, redeposits it again in the form of a calcareous cement. Some of this stone presented very distinct examples of the oolitic structure presently to be mentioned, little minute grains and particles being enveloped in one or two concentric coats, like the coats of an onion. That this stone was not consolidated under water was proved by nests of turtles' eggs being found embedded in it, evidently deposited by the animal when the sand was above water, and was loose and incoherent.

Guided by these facts and observations, we may form tolerably accurate notions of the mode of origin of all our marine limestones, and attribute to them an organic-chemical origin, taking into account, at the same time, how easily they may have been subsequently altered in texture by the metamorphic action either of water or of heat.

We must also bear in mind that, although the carbonate of lime may have been secreted and brought into a solid form from its aqueous solution by the action of animal life, yet that the original form it thus received has been retained in only a small part of it; the great mass having been subjected to the mechanical actions of erosion, trituration, and transport, to a greater or lesser extent, in the process of its conversion into calcareous sand and mud, and deposition as beds of limestone.

Fresh-water Limestones.—Those limestones which have been formed in fresh-water lakes, and are called fresh-water limestones, may more nearly resemble travertine in their mode of origin, since there is nothing to forbid the supposition of the waters of lakes becoming so highly impregnated with dissolved carbonate of lime as actually to deposit it as a chemical precipitate. At the same time, most fresh-water limestones look more like the result of the deposition of a highly calcareous, rather clayey mud, than of a precipitate of pure carbonate of lime. They become then the extreme term of marl or calcareous clay, and may be the result of either the disintegration of shells, &c., or of the mechanical action of rivers on previously existing calcareous rocks, the calcareous mud thence derived being perhaps mingled with the detritus of other rocks in greater or less quantity.

Silica.—The aqueous deposition of silica is sometimes a purely chemical one, as in the case of the siliceous sinter deposited round the Geysers, or hot springs, of Iceland; and round the hot springs of St Miguel and Terceira, in the Azores; and the chalcedony round those of New Zealand. Cold-water springs also, in some instances, deposit siliceous matter; but in these the silica is generally combined with alumina, oxide of iron, and other bases. In all these cases, evaporation of the water takes place; and Bischof attributes the formation of quartz crystals in cavities, and of compact quartz in veins, to the total evaporation of water containing silica in solution, and trickling down the sides of such cavities. He shows the impossibility of ascending springs depositing the quartz, insomuch as those must be full of water, and therefore total evaporation of successive films of water could not take place. He attributes the formation of quartz crystals in drusy cavities to a similar evaporation of water containing silica, that has filtered through the adjoining rock. Agates, chalcedony, &c., show very distinctly the successive deposition of films of silica.

Marine Flints.—To account for the deposition of silica on the bed of the sea, where evaporation is not possible, we are compelled, as in the case of limestone, to call in the aid of the powers of animal life. The minute shells of many of the infusoria are almost entirely composed of silica, which they have extracted from the water of the sea. Some kinds of rock, such as the tripoli, or polishing slate, are entirely made up of these microscopic substances, some beds thus formed being many fathoms in thickness and many miles in extent.

All seas, from the equator to the poles, abound with these minute organisms. They have been found living even in ice. The phosphorescence of the sea, also, is due to the presence of organic beings, a large proportion of which are siliceous-cased animalcules. The bottom of the mid-Atlantic, at a depth of 2000 fathoms, was found, in some of the late hydrographic surveys of the United States, to be covered by what appeared to be a fine clay; but this, on examination, was discovered to be entirely composed of the siliceous shells of infusoria. According to Ehrenberg, there are formed annually in the mud deposited in the harbour of Wismar, in the Baltic, 17,946 cubic feet of siliceous organisms. Although it takes a hundred millions of these animalcules to weigh a grain, Ehrenberg collected a pound-weight of them in an hour. So prolific are they, moreover, that "a single one of these animalcules can increase to such an extent during one month, that its entire descendants can form a bed of silica 25 square miles in extent, and 13 foot thick." As a parallel to Archimedes, who declared he could move the earth if he had a lever long enough, we may say—Give us a mailed animalcule, and with it we will in a short

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1 See Dr Carpenter's papers on these creatures in the Philosophical Transactions. The silica thus rendered solid, may either be deposited alone, or may be associated, as will most probably be the case, with the debris of calcareous matter forming marine limestones, and having an equally organic derivation. When thus diffused in the finest particles, pretty equally perhaps through the mass of calcareous mud, it may either be consolidated in this equally diffused state, producing a more or less siliceous limestone, or it may, in obedience to certain chemical laws, segregate itself from the calcareous matter, and form either distinct layers and veins, or concretionary balls and nodules. The presence of any body itself consisting largely of silica, such as many sponges, will facilitate and determine this process, affording a centre of attraction for the siliceous particles to collect around it from the adjacent matter.

These views of the organic origin of most marine limestones and flints are corroborated by the fact, which we shall presently describe, of almost all great masses of limestone being accompanied by siliceous portions of a peculiar character, such as are not found in any other rocks except limestone.

Carbonate of Magnesia.—Magnesia occurs in sea-water in the form of chloride of magnesium and sulphate of magnesia. Of the solid salts dissolved in sea-water, 8 to 15 per cent. consists of chloride of magnesium, and 6 to 16 per cent. of sulphate of magnesia. (Bischof, vol. i., p. 99-105.) From the quantity of free carbonic acid in the sea, it is plain that these might be converted into carbonate of magnesia, but that if so, it would be kept in solution as a bicarbonate (sesqui-carbonate), as in the case of carbonate of lime. All that has been said, therefore, as to the necessity for calling in the aid of organic life to solidify carbonate of lime from the waters of the sea, "holds good in regard to carbonate of magnesia, and the more so since this salt always separates later than carbonate of lime, even from fluids which have undergone a very high degree of evaporation." (Bischof, vol. i., p. 117.)

There is, however, this difficulty in this view,—the carbonate of lime is largely separated from the sea-water by being made to enter into the composition of the hard parts of marine animals in overwhelming proportion, whereas the percentage of carbonate of magnesia to be found in the hard parts of corals and molluscs does not exceed 1 or 2 per cent. Neither do we know any class of animals that secrete any much greater quantity of magnesia as some of the infusorial animals secrete silica. Yet in many widely-spread magnesian limestones the quantity of magnesia is almost equal to that of lime, and the proportion is frequently as much as 20 to 30 per cent. According to Forchhammer, the fucoid marine plants contain more than 1 per cent. of magnesia; but the remains of such plants are rarely if ever found in magnesian limestones. Magnesian limestones are, moreover, generally poor in organic remains, though this may be the result of their more perfect crystallization and mineralization in various ways, by which the organic structure has been obliterated, rather than of the absence of organic beings from the original deposit.

In whatever way effected, it is true that magnesian limestones, containing various proportions of lime and magnesia, have been deposited originally as magnesian limestone at the bottom of the sea, sometimes in large quantities, and over considerable areas.

It is equally true that pure carbonate of lime has in many cases been subsequently converted into dolomite or magnesian limestone by chemical metamorphic action.

The resemblance which magnesian limestones, even where the carbonate of magnesia is in comparatively small proportion, bear to true dolomites, and their likeness to a chemical precipitate rather than to a mere sedimentary deposit, induce us to pause before denying altogether that such precipitation of carbonates, whether of lime or magnesia, have taken place on the bed of the sea without the intervention of organic life.

Sulphate of Lime and Rock-salt (chloride of sodium) are undoubtedly chemical precipitates, and we are here again met by the same difficulty as before, in assigning a proximate cause for that precipitation in the open sea. If we could imagine a portion of sea-water separated from the ocean, and left as a shallow lagoon to gradually dry up, there would be no difficulty in the case.

Bischof gives the following as the average composition of the salts of the sea-water (vol. i., p. 379):

| Saline contents of sea water | Per cent. | |-----------------------------|----------| | Consisting of— | | | Chloride of Sodium (common salt) | 75-786 | | Chloride of Magnesium | 9-159 | | Chloride of Potassium | 3-627 | | Bromide of Sodium | 1-184 | | Sulphate of Lime (gypsum) | 4-617 | | Sulphate of Magnesia (Epsom salts) | 5-597 |

He tells us too, that when sea-water is evaporated, the point of saturation for sulphate of lime is much sooner reached than that for rock-salt; 37 per cent. of the water being required to be removed in the one case, and 93 per cent. in the other. Gypsum, therefore, must always be deposited before rock-salt, and it is possible for the point of saturation to be reached for gypsum in many cases without that for rock-salt being attained. This may be the reason why, although the sea contains sixteen times as much salt as it does gypsum, that the latter more frequently occurs as a mineral deposit than the former, though not often in such great masses.

In isolated seas, such as the Dead Sea, where the water is entirely saturated with salt, evaporation doubtless causes a precipitation on its bed (Bischof, p. 400). Here, and in shallow lagoons, such as the limans of Bessarabia, south of Odessa, that dry up in summer, we have the formation of rock-salt going on before our eyes.

In fresh-water lakes, sulphate of lime may be deposited, either directly, the water becoming saturated with that substance, or in consequence of springs or rivers containing sulphuric acid, which convert into sulphates the carbonates of the marls and calcareous muds already deposited. In some instances chemical reactions, such as the oxidation of iron pyrites (bisulphuretted iron), and that of sulphuretted hydrogen, may be supposed to take place, producing sulphuric acid, which immediately acts on any carbonate of lime that it can reach.

Carbon may be looked upon as essentially an organic element. Wherever we find carbonaceous matter in rocks, therefore, we may suspect it to have been derived from organic substances. Even the diamond is now believed to be a crystalized gum, or other vegetable product; and graphite may in like manner be looked upon as a possible, if not a probable, result of the metamorphosis of either animal or vegetable substance into a mineral. Even the purest graphite contains traces of earthy matter, diminishing its claims to be considered an original independent substance.

Carbon enters into the composition of animal matter, but its most abundant source is the vegetable kingdom.

Again taking Bischof as a guide in the explanation of the conversion of the organic substance wood into the rock Geology, which we call coal, we abstract some of his results in the following remarks:

Table of the Composition of Carbonaceous Substances:

| Substances | Carbon | Hydrogen | Oxygen and Nitrogen | |------------|--------|----------|--------------------| | Wood | 49-1 | 6-3 | 44-6 | | Peat | 54-1 | 5-6 | 40-1 | | Lignite | 69-3 | 6-6 | 25-3 | | Coal | 82-1 | 5-5 | 12-4 | | Anthracite | 94-0 | 3-0 | 3-0 |

In addition to these elements, however, the four latter substances given above contain variable quantities of earthy impurities, which are given, as in

Peat: from 4-8 to 10 per cent. Lignite: 0-8 to 47-2 Coal: 0-24 to 25-5 Anthracite: 0-94 to 7-07

Looking on these earthy matters as accidental and unessential, we learn from the examination of the above table, that the rocks anthracite, coal, and lignite, and the intermediate substance peat, consist of the same constituents as the organic substance wood, the differences between them being in the proportions in which these constituents occur.

No other rocks except the coals have a composition at all similar to this.

If we abstract from wood some 30 per cent. of its oxygen and nitrogen, and compress the remainder till it becomes more dense and compact, it must form coal.

If, therefore, we suppose wood (or vegetable matter) buried under accumulations of more or less porous rock, such as sandstone and shale, so that it might rot and decompose, and some of its elements enter into new combinations, either gaseous or liquid, those combinations always using up a greater quantity of oxygen and nitrogen than of carbon and hydrogen, or of oxygen and hydrogen than of carbon, we should have the exact conditions for the transformation of vegetable matter into coal.

This process might naturally take place in four ways:

1st. By the separation of carbonic acid gas (consisting of two equivalents of oxygen and one of carbon=CO₂) and carburetted hydrogen (consisting of four equivalents of hydrogen to two of carbon=C₂H₄) from the elements of the wood.

2nd. By the separation of carbonic acid from the elements of the wood, and the oxidation of some of the hydrogen (i.e., its conversion into water=HO) by combination with external oxygen.

3rd. By the separation of both the carbonic acid and the water from the elements of the wood.

4th. By the separation of all three substances, carbonic acid, carburetted hydrogen, and water, from the elements of the wood.

The loss of carbon is greatest in the first case, and least in the third, being always greater in proportion to the quantity of carburetted hydrogen which is disengaged.

The great quantities of carbonic acid gas (choke damp) and carburetted hydrogen (fire damp) met with in coal mines, shows the fact of the large extrication of these substances, and corroborates, if need were, this explanation. Reservoirs of these gases in a highly compressed state are often found to be pent up in the crevices and cavities of coal beds, and are the cause, when tapped, of many of the accidents which take place. Some beds of coal are so saturated with gas, that, when cut into, it may be heard oozing from every pore of the rock, and the coal is called "singing coal" by the colliers.

Bischof shows, that "under circumstances otherwise similar, the conversion of vegetable substances into coal takes place in the same way, whether they are mixed with much or little earthy matter." He also believes, from Kremer's and Taylor's investigations into the nature of the ash of coal, that there was an intimate mixture of vegetable and earthy substances, and that coal containing earthy matter could not be formed from compact wood without previous decay having taken place (vol. i., p. 269). He seems to suppose that, in many instances, this decay has gone so far as to convert the vegetables into "mould," which has been drifted as a kind of vegetable mud, and when mixed with earthy matter, deposited under water in the place where we now find it as coal.

From these preliminary considerations, we learn that plants living in the air extract from it the invisible carbonic acid and other gases, and by the hidden processes of life, compel them to enter as solid and visible substances into the composition of their own bodies; and that animals living in the sea, in like manner extract from it the invisible solutions of lime and other substances, and similarly compel them to become solid and visible parts of their own bodies. In each case the substances thus rendered visible and solid by the action of organic laws, become, after the death of the organism, subject to the ordinary laws governing inorganic matter, and after undergoing more or less alteration, are used as materials for assisting in the construction of the external crust of our earth.

Description of the Chemically and Organically formed Aqueous Rocks.

55. Limestone may be hard or soft, compact, concretionary, or crystalline, consisting of pure carbonate of lime, or containing silica, alumina, iron, &c., either as mechanical admixtures, or as chemical deposits along with it.

Different varieties of limestone occur in different localities, both geographical and geological, peculiar forms of it being often confined to particular geological formations over wide areas, so that it is much more frequently possible to say what geological formation a specimen was derived from, by the examination of its lithological characters, in the case of limestone, than in that of any other rock.

Compact limestone is a hard, smooth, fine-grained rock, generally bluish gray, but sometimes yellow, black, red, white, or mottled. It has either a dull earthy fracture, or a sharp, splintery, and conchoidal one. It will frequently take a polish, and when the colour is a pleasing one, is used as an ornamental marble.

Crystalline limestone may be either coarse or fine-grained, varying from a rough granular rock of various colours, to a pure white, fine-grained one, resembling loaf sugar in texture. This latter variety is sometimes called saccorhine, sometimes stony marbles. The crystalline structure of limestone is either original, when it is often found that each crystal is a fragment of a fossil; or it has been superinduced by metamorphic action on a limestone formerly compact.

Chalk is a white, fine-grained limestone, sometimes quite earthy and pulverulent, sometimes rather harder and more compact, as the chalk of the north of Ireland, and some of that of the north of France.

Oolite is a limestone in which the mineral has taken the form of little spheroidal concretions, and the rock looks like the roe of a fish, from which its name, signifying egg, or roe-stone, is derived. These little concretions have several concentric coats, sometimes hollow at the centre, some-

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1 See also a very clear explanation of this subject in Ronald's and Richardson's Chemical Technology, vol. I., p. 31.

2 Although coral-reefs were dwelt on as the most obvious and abundant source of limestone at the present day, it was not intended to infer that they had always been so. The older limestones have none of the huge reef-making corals in them; the small corals they contain merely contributed to their formation, together with other animals that secreted carbonate of lime.

3 No experienced British geologist would be likely to confound characteristic specimens of the limestones of the Silurian, Carboniferous, Oolitic, and Cretaceous formations of Britain and Western Europe; while any one might easily mistake the argillaceous or arenaceous rocks of those different formations. times enclosing a minute little grain of siliceous, or calcareous, or some other mineral substance. It is commonly of a dull yellow colour, but gray oolitic limestone is not unfrequent. Its peculiar structure gives it the character of a freestone, working easily in any direction; whence its value as a building stone.

Bath stone, Portland stone, Caen stone, are well-known examples of oolitic limestone.

Pisolite is a variety of oolite, in which the concretions become as large as peas. It is a structure not confined to limestone, however, as other rocks or minerals occasionally assume it.

Many limestones are named from their containing some peculiar variety of fossil, as nummulite, clymenia, crinoidal limestone, and shell limestone, or muschelkalk.

Others have local names given them, as the calcaire grossier of Paris, a coarse limestone, some beds of which are used for building, while others are a mass of broken shells.

Cipolino, a granular limestone containing mica; majolica, a white, compact limestone; scaglia, a red limestone in the Alps. (Murchison and Nicol, in Johnston's Physical Atlas.)

Ireland especially abounds in a great variety of limestones used for ornamental marbles, such as the green serpentine-marble of Ballynahinch in Galway; the black marble of Kilkenny; the brown, red, and dove-coloured marble of Cork and Armagh; and many others less known, and some of them unworked, but equally beautiful with those that are. In Derbyshire and North Staffordshire, we have a similar abundance of ornamental marbles.

Fresh-water limestones have commonly a peculiarity of aspect, from which their origin may sometimes be suspected, even before examining their palaeontological contents, or petrological relations. They are generally of a very smooth texture, and either dull white or pale gray, their fracture only slightly conchoïdal, rarely splintery, but often soft and earthy.

Flint and Chert.—The association of flints with chalk is well known. Chalk flints occur as rounded nodular masses, of very irregular, and sometimes fantastic shape, and of all sizes, up to a foot in diameter. They are commonly white outside, but internally are of various shades of black or brown; sometimes passing into white. They have sometimes concentric bands of black and white colours internally, and exhibit markings derived from organic bodies round which they have often been formed. Flint occurs in chalk not only in nodules, but also in seams or layers, sometimes short and irregular, sometimes regular, over a distance of several yards. These seams vary from half an inch to two inches in thickness, and are commonly black in colour.

Almost all large masses of limestone have their flints or siliceous concretions. These are frequently called chert, as in the carboniferous limestone, where the nodules and layers of chert exactly resemble the flints in chalk.

Even the tertiary limestones around Paris have their flints, the melainite of that locality being nothing but a siliceous concretion, found in the Calcaire St Ouen, and possibly other places.

Pure siliceous concretions occur even in the freshwater limestones and gypsum beds of Montmartre.

This invariable, or nearly invariable accompaniment of limestone and siliceous deposits,—those siliceous parts having a chemical, and not a mechanical formation,—strengthen the hypothesis of the organic origin of both, as previously described.

The silica diffused through the calcareous mud, of which the limestone was composed, has sometimes remained so diffused, instead of separating as nodules or layers, producing a cherty or siliceous limestone.

Clay, or argillaceous matter, has frequently been deposited with the calcareous, producing argillaceous limestone, which may be known by the earthy odour given out by it when breathed upon.

Carbonaceous matter, derived either from decaying vegetables, or perhaps more frequently from the decomposing animals of whose hard parts the rock is composed, produces in like manner the black limestones, which are in some instances called bituminous limestones. Little nests of pure anthracite, or other variety of carbonaceous matter, are sometimes found in the hollows of shells buried in limestone.

The fetid smell, like that of sulphurated hydrogen gas, given off by many limestones when struck with a hammer, is probably another result of the decomposition of animal matter, producing what is called "fetid limestone," or, by the Germans, "stinkstein."

When the argillaceous has been mingled with the calcareous matter in very large proportion, a subsequent separation of the two has often taken place, the lime having aggregated itself from the mass in this case, as the siliceous separated from the calcareous matter in the case of flints and chert. Nodular lumps of limestone are then produced, divided from each other by little, often irregular, seams and layers of shale or clay. These concretionary lumps of limestone are sometimes merely scattered through the clay, but they often form regular seams or beds, the upper, or under, or both surfaces being uneven and nodular. It is sometimes difficult to say whether the little parting films and small seams of clay which occur between the beds have been deposited at different times from the calcareous matter, or having fallen together with it as an argillo-calcareous mud, have had their calcareous particles sucked out of them, as it were, by the segregating influence of chemical affinity.

It is by no means intended to infer that alternate deposits of thin layers of calcareous matter and purely argillaceous or arenaceous matter have not frequently occurred; we only wish to put the student on his guard against taking particular structures as proofs of original deposit, which, especially in so active and unstable a substance as carbonate of lime, may in many instances be the result of subsequent agency. It is comparatively rare to find such a mingling of quartzose sand and lime as could be called arenaceous limestone, though we have already seen that calcareous sandstones are not uncommon. Scattered pebbles, however, are sometimes found in chalk and other limestones; and a curious instance, first noticed by Professor Haughton, occurred at Crumlin, near Dublin, of angular fragments of granite, several inches in diameter, accompanied by granitic sand, being found embedded in limestone, four or five miles from any known granitic mass in situ. Such fragments may perhaps have been floated in the roots of trees and other vegetables, just as in the present day pebbles of hard stone, highly valued by the natives, are found in the roots of trees cast up upon the shore of archipelagoes of coral islands in the Pacific, as mentioned by Chamisso and Darwin.

Magnesian limestone.—Carbonate of magnesia is often found in marine limestones, mingled in various proportions with the carbonate of lime. Its occurrence in small quantity frequently gives a sandy appearance and gritty feel to an otherwise smooth and compact limestone. When examined with a lens, this apparent sand is found to be made up of minute dolomitic crystals, commonly of a yellowish brown colour, and with a pearly lustre.

In a true magnesian limestone the crystallization and the pearly lustre is generally very distinct, though sometimes the crystals are minute. Its colour is commonly some shade of brown or yellow, occasionally tinged with red; gray and black varieties, however, occur sometimes over very large areas.

Magnesian limestone is very variable in lithological character. It is sometimes of a powdery, earthy, and friable texture; sometimes splits into thin slabs, some of which are flexible; sometimes forms singular concretionary masses, a number of balls touching each other, either like bunches of grapes, when it is called botryoidal, or like musket balls, or great piles of cannon shot. Many of these balls, on being broken open, are found to have a radiated structure. That all these curious forms have been produced subsequently to the deposition of the mass is shown by the fact of the lines of deposition or stratification proceeding through them regularly, without regard to the spherical outlines or radiated structure of the balls.

Magnesian limestone occurs in two forms, original and metamorphic. In some limestones the carbonate of magnesia has clearly been deposited together with the carbonate of lime, the whole having been originally formed as a magnesian limestone.

In other instances, it can be shown, from the geological conditions that whether the rock originally contained magnesia or not, its present distribution and mode of occurrence, and its highly crystalline structure, are the result of agencies operating subsequently to the original formation of the rock, and affecting a number of different beds simultaneously, along certain narrow lines of fissure, to the neighbourhood of which the dolomitized condition of the rock is confined.

57. Gypsum occurs as a rock in various ways. It sometimes forms regular beds, sometimes irregular concretionary masses, sometimes veins and strings in the mass of other rocks.

Compact Gypsum or Alabaster¹ is one variety; granular, finely crystalline gypsum another. The thin beds and the veins and strings of gypsum are commonly fibrous, the fibres being at right angles to the beds. The gypsum of Montmartre, from which plaster of Paris is derived, is chiefly granular gypsum, each bed being composed of many layers of little crystals, slightly differing in colour and texture, and thus assuming a regularly laminated appearance. This would lead us to suppose that this rock, which is associated with fresh-water limestones and marls, was formed by the periodical deposition of layers of small crystals of sulphate of lime at the bottom of the water.

In August 1855 we observed in the quarries north of Montmartre one or two beds, six or eight inches in thickness, of beautifully crystallized sulphate of lime, in large perpendicular plates, interstratified with these little layers of crystals. All the beds were horizontal; and the layers of small crystalline grains were quite parallel to the stratification; but in the beds above mentioned, the crystalline plates, instead of being parallel to the lamellar form, had struck directly across the bed, more or less nearly at right angles to it, the original horizontal lamination not being obliterated, but being in some places waved, as if slightly disturbed by the formation of the crystalline plates, the angles of these waves having evident relation to the faces and angles of the superinduced crystalline plates.

This formed a good case, like that before-mentioned as occurring in the spheroidal concretions of magnesian limestone and other rocks, of a molecular change of structure having taken place in the mass of the rock subsequently to its formation. It yet remains for the chemist to explain to us the exact method of operation by which these changes are produced.

58. Rock-salt commonly occurs in Britain as a rudely crystalline, irregularly bedded mass, commonly stained of a dirty red by the mixture of feruginous clay and other impurities. Perfect cubical and transparent crystals occasionally occur, and curious spheroidal bands, of a white colour, are sometimes observable in the roof of a salt-mine. Bed-like masses of rock-salt are often 60 or 90 feet thick, thinning out probably in all directions, and thus taking the form of large cakes. In other countries, more numerous beds occur, but not making up larger masses. In some of these the salt is perfectly pure and white; but in all countries, and in all geological formations, the association of salt with gypsum, and with green, red, and variegated marls, is a frequent if not invariable occurrence. We have already seen how natural and almost inevitable is the occurrence of gypsum with rock-salt; but the accompaniment of red and variegated clays has not yet been explained. When it is, it will probably throw great light on the circumstances under which the rock-salt itself has been deposited. Dolomite is also often found in connection with rock-salt.

59. Coal is a rock the general aspect and nature of which is familiar to everybody. Its chemical composition has been spoken of above, and the resemblance of that composition to that of wood, and the way in which, by a slight alteration in the proportion of its component parts, and an accompanying physical consolidation, the one may be converted into the other. Coal is very commonly divided into bituminous and non-bituminous. Now bitumen is rather a vague term, including several combustible substances, such as asphalt or mineral pitch, elastic bitumen or mineral exocathouc, naphtha, petroleum, &c. These bituminous substances are all either fluids, or are readily soluble in naphtha. It is, however, impossible to dissolve any appreciable portion of coal in naphtha, which shows that it does not contain any actual bitumen, though it may contain the

¹ Alabaster is derived from Alabastro, a town of Egypt, where it was manufactured into boxes for ointment. The term "alabaster" was then applied to carbonate of lime, as well as sulphate of lime. constituents of it. The natural and artificial bitumens are the result of the decomposition of vegetable matter, and may be extracted also from coal by subjecting it to distillation. They always contain from 7 to 94 per cent. of hydrogen, combined with carbon and oxygen. The so-called bituminous coals, then, are those in which the mineralizing process has only proceeded to a certain extent, leaving a considerable proportionate amount of hydrogen and oxygen in their composition; while those called non-bituminous are those from which a greater quantity of the latter substances have been extracted, and a larger proportion of carbon left behind. If the decomposition of wood results in the formation of carbonic acid gas, which takes away both carbon and oxygen, or of carburetted hydrogen, which takes away a large proportion of carbon, the carbon in the remainder will not be in such excessive proportion, and the constituents of the resulting coal will more nearly resemble those of bitumen. In this sense they may be called bituminous coals.

If, however, a large portion of the oxygen and hydrogen be extracted, either as water or in any other form, the proportion of carbon in the remainder becomes excessive compared with that in the composition of bitumen; and hence the coals may be called non-bituminous.

Coals vary greatly, not only in the proportions of their essential constituents, carbon, hydrogen, and oxygen, but also in the amount of earthy matter (forming ash) which has been accidentally and mechanically mingled with those constituents. We have seen that the percentage of ash is sometimes as much as 35 per cent. in coals that have been regularly analysed. In poorer varieties of coal, however, such as are never brought to market, but which are occasionally used in particular localities, this percentage is doubtless still greater; and we have in nature every gradation, from pure coal into a mere carbonaceous (commonly called bituminous) shale or "batt," which often contains enough inflammable matter to give out flame and support combustion for a time when burnt with better coals, but soon passes into a lump of ash, unaltered in form, and not retaining heat longer than a brickbat would under similar circumstances. These batts, shales, or slates, often accompany coal, being found not only either just above or just below it, but in it, in the form of thin seams, layers, or cakes, which are often not to be separated from it without some trouble.

Just as limestone is often mingled with clay, and passes through argillaceous limestone and calcareous clay (or marl) into clay itself, so coal passes through earthy or ashy coal, and carbonaceous shale, into common shale or clay, no very hard boundary-line being to be drawn between the many minor graduating varieties of the different substances.

Discarding the impure or imperfect coals, the recognizable varieties of true coal are sufficiently numerous. They may be grouped under three heads—Anthracite, ordinary or pit-coal, and brown coal or lignite.

Brown coal or lignite sometimes shows the structure of the plants from which it is derived but little altered from their original condition; stems with woody fibre crossing each other in all directions. It is of a more or less dark colour, soft and mellow in consistence when freshly quarried, but becoming brittle by exposure, the fracture following the direction of the fibre of the wood." (Chemical Technology, Ronalds and Richardson, vol. i., p. 32.)

"Other kinds present only occasional distinct indications of vegetable structure, and appear throughout as a stratified mass of a dark, nearly black colour, with an earthy fracture; while in some varieties the structure is still more dense, and the fracture is conchoidal."—Ib.

The latter varieties, as in the case of the Bovéy coal of Devonshire, are often scarcely distinguishable by any external characters from some varieties of ordinary coal.

Ordinary or pit-coal has many varieties; indeed these are often as numerous as the different seams of a coal-field, and even the different beds of a compound seam are readily distinguished from each other by the colliers, who give particular names to them; and even small blocks of these varieties can be recognised by them, and identified with the seam, or part of a seam, from which they are derived. Neither are these distinctions, which are only to be perceived after long practice, unimportant, since these varieties have distinct qualities, some of them being better adapted to smelting, and said to be "good furnace coal;" some of them to blacksmith's work, or "good shop coal;" others to various uses; while only a few, comparatively, are best fitted for domestic purposes, and are brought to market by the coal-merchant.

Some idea of the immense varieties of coal may be gained from an inspection of the report of the Admiralty coal Investigation (Mem. Geol. Survey, vol. i.), as well as from the varying qualities of those which we are in the habit of using daily in our houses. "As many as seventy denominations of coal are said to be imported into London alone." (Chem. Tech.)

All these minute varieties are commonly included under four principal heads—1. Coking coal; 2. Splint, or hard coal; 3. Cannel or parrot coal; and 4. Lignite, or parrot coal.

Coking coal is so named from its fusing or running together on the fire, so as to form clinkers, requiring frequent stirring to prevent the whole mass being welded together. It breaks commonly into small fragments with a short uneven fracture. The Newcastle coal, and many others from different localities are coking coals. They leave many cinders and a dark dirty ash.

Splint or hard coal is well known in the Glasgow coal-field. It is not easily broken, nor is it easily kindled, though, when lighted, it affords a clear, lasting fire. It can be got in much larger blocks than the coking coals.

"Cherry or soft coal is an abundant and beautiful variety, velvet black in colour, with a slight intermixture of gray. It has a splendid or shining resinous lustre, does not cake when heated, has a clear shaly fracture, is easily frangible, and readily catches fire." (Chem. Tech.) It leaves comparatively few cinders, and its ash is white and light. It requires little stirring, and gives out a cheerful and hot heat. The Sunderland coals principally belong to this variety.

Cannel or parrot coal is called cannel from its burning, with a clear flame like a candle, and parrot in Scotland from its crackling or chattering when burnt. Cannel coal varies much in appearance, from a dull earthy to a brilliant shiny and waxy lustre. It is always compact, and does not soil the fingers. Its fracture is sometimes shaly, sometimes conchoidal. The bright shining varieties often burn away like wood, leaving scarcely any cinders and only a little white ash. The duller and more earthy kinds leave a white ash, retaining nearly the same size and shape as the original lumps of coal. Cannel coal often takes a good polish, and can be worked into boxes and other articles. Jet is an extreme variety of cannel coal in one direction, an batt or carbonaceous shale is in another.

Anthracite is heavier than common coal, with a glossy, often iridescent lustre, and a more completely mineralized appearance. It rarely soils the fingers, has a distinctly sharp-edged conchoidal fracture, or else breaks readily into small cubical lumps. It is not easily ignited, but when burning gives out an intense heat, so as to sometimes melt the bars of the grate or furnace in which it is used. It does not flame, and gives off but little smoke, being in this respect similar to coke or charcoal.

In many ordinary coals, little flakes of mineral charcoal occur, retaining that part of the vegetable structure called the vascular tissue. They are called "mother of coal" by the colliers in some places. "It is frequently seen in the form of a thin silky coating, covering some of the surfaces of the coal." (Professor Harkness on Coal, Edinburgh New Philosophical Journal, July 1854.) Microscopical examination exhibits not only the vascular but the cellular tissue of plants in the substance of many coals, as was shown by Mr Witham in his work on the structure of fossil plants, and by many observers since.

All coals have a peculiar structure, which bears a slight analogy to crystallization. They break or split not only along the bedding, but across it, along two set of planes at right angles to the bedding and to each other. The smooth, clean faces produced by one of these division planes are more marked and regular than that produced by the other, as may be seen by examining any lump of coal. The principal of these division planes are called by the colliers the face of the coal, the other being called the back or end of the coal. They preserve their parallelism sometimes over very wide areas; and the mode of working or getting the coal, and the direction of the galleries, is governed by the direction of the face. In some places these division planes are called "cleat," in others "slines."

It is a structure which is probably the result of the mineralizing process undergone in passing from an organic to an inorganic state, and may be likened perhaps to the "cleavage" of a mineral rather than to either the true "slaty cleavage of rocks, or to their "foliation" or "jointing"—structures that will be hereafter described.

III.—AERIAL ROCKS.

Although the amount of rocks, or accumulations of earthy matter, formed of materials which were brought into their present situation by the action of the wind, is comparatively of small importance, it is not expedient wholly to overlook this action. Along all low sandy coasts hills are formed of drift sand, which sometimes attain a considerable altitude, as much, for instance, as 200 or 300 feet. These hills are commonly called "dunes." They have been described as advancing on the low shores of France, in the Bay of Biscay, at the rate of 60 and 70 feet per annum, overwhelming houses and farms in their progress. Similar accumulations take place on the coast of Cornwall, where the sand, composed largely of fragments of shells and corals, becomes converted sometimes into a hard stone by carbonate of lime or oxide of iron. (De la Beche's Manual.)

Lieutenant Nelson has described similar aerial accumulations in the Bermuda Islands, giving them the name of Eolian rocks.

Along the south coast of Wexford, as also in Smerwick harbour (county Kerry), and other parts of the British Islands, similar accumulations are in progress.

On the eastern coast of Australia, about Sandy Cape, this process is going on on a still larger scale. In Port Bowen, in the same neighbourhood, we once saw a very good instance of it. The rise and fall of the tide there is as much as 16 feet; and at low water great sand-banks are exposed, derived from the shallow sea outside and the waste of the porphyritic rocks on the coast. These sand-banks rapidly dry under the hot sun; and the trade-wind, which blows home upon the shore, then drifts the sand up upon the beach, and piles it into hills 50 or 60 feet high. Behind these hills is a large mangrove swamp, which is being gradually buried under the advancing sand, some of the mangrove trees only just peering above it, others half covered, and so on. The drift of sand through the gaps of these dunes was exactly like a snow-drift in a heavy storm whenever the wind blew freshly.

Large districts, with hills of 200 or 300 feet in height, are found also on the coasts of Western Australia, stretching sometimes 10 miles inland, formed of loose incoherent sand, once apparently drifted by the wind, though now brought to rest by the growth of a wide-spread forest of gum-trees. Parts of these sands, which consist greatly of grains of shells and corals, are compacted together into a stone, hard enough to be used for building, by the action of the rain-water dissolving some of the carbonate of lime, and redepositing it on evaporation. Curious cylindrical stems, from 1 inch to 18 inches in diameter, are there seen projecting from the soil, and have been taken for petrified trees, which they greatly resemble; but we observed, in 1842, a number of these supposed trees exposed in a little cove, south of the entrance of Swan River, ending downwards in tapering forms like stalactites; and we believe them, therefore, to have a stalactitic origin, due to the percolation of water down particular pipes and channels in the sand.

Nor is it along the coast only that such accumulations are taking place. In the interior of great dry continents, there are vast spaces covered with sand and sand-hills, which are shifted and carried about by the wind, just as some sand-banks are deposited now here, and now there, carried about by the water. We have but to recall to the mind of the reader the well-known stories of caravans crossing the desert being met and sometimes overwhelmed by moving columns of sand, and the way in which many of the temples of Egypt have been buried under such accumulations, for him to see that this action cannot be altogether overlooked. Egypt would probably have been long ago obliterated by drift-sand if it had not been for the Nile, and the strip of vegetation that accompanies and defends it. In the interior of Australia, Captain Sturt reports the existence of vast deserts of sand, with long lines of great sand-hills, 200 feet high, the base of one touching that of its neighbours, and all stretching in straight lines each way to the horizon.

It would be quite proper also to class among aerial rocks such accumulations of tuff as were derived from volcanic ashes falling on the land, and also the masses of pebbles, cinders, and fragments so derived, were it not more convenient to describe them in connection with the volcanic rocks, so as not to separate in our account those falling on the land from those deposited in water.

Soil.—The accumulation of decayed vegetable matter, mingled sometimes with animal, always with earthy mineral matter, which is called "soil" or "mould," is also an aerial process, deserving of more attention than it has yet received. Soils sometimes occur as distinct rocks, interstratified with other rocks.

CHAP. IV.—THE METAMORPHIC ROCKS.

Preliminary Observations.

In the course of the foregoing descriptions we have mentioned the segregation into concretionary lumps and nodules, of siliceous from calcareous matter, and of calcareous from argillaceous; and we have described the radiated and concretionary forms assumed sometimes by magnesian limestone and the re-arranged crystallized beds of gypsum. These, however, are not the only instances of such separation of parts, and assumption of new forms and combinations, by the particles of rock after their deposition, and after their more or less complete consolidation. Any mineral diffused in a state of minute division through a mass of different nature from itself, seems to have tendency to segregate itself from the mass, and collect together upon certain points or centres. Iron, either in the form of iron pyrites (bisulphide of iron), or ironstone (clayey carbonate of iron), or haematite (oxide of iron), frequently forms such concretionary lumps. Iron pyrites, either in cubical crystals, or in balls with an internal radiated structure, is frequent in all argillaceous and calcareous rocks, and in many trap rocks. Ironstone forms regular layers of round nodules, sometimes as much as a foot or 18 inches in diameter, in many argillaceous rocks. These nodules, when broken open, are often found to be traversed by cracks in all directions, more or less filled up with crystalline spars (carbonate of lime, &c.), together with crystals of galena, blende, iron pyrites, and other minerals.

In other clays, carbonate of lime, mingled perhaps with iron, produces similar stones, called septaria or cement stones in some places. They often take a polish, and the sparry veins produce a variously ornamented appearance.

In these septaria and ironstone balls the external crust is generally smooth and compact, the internal cracks becoming larger and more numerous as they proceed towards the centre. As the cracks are obviously the result of desiccation and consequent contraction, and as the external crust would naturally be the first part to consolidate, it does not at first seem obvious why the cracks should not occur outside rather than in.

Professor Hennessy, however, remarked to us, that in the case of volcanic bombs, which have a similar structure, the fact of the preliminary consolidation of the external crust was the cause of the internal fissuring; since, when that was formed, no farther shrinking or contraction of the whole body could take place; and the internal parts being thus relieved from external pressure, would shrink and contract among themselves, being rather attracted towards the dense external crust than towards the centre. If consolidation commenced at the centre, the whole nodule would have contracted towards the centre, and thus have shrunk into a less size and a denser state, without the occurrence probably of either external or internal cracks.

Hematite, whether red or brown, affects a kidney-shaped concretionary form, often hollow, with a minutely radiated structure at right angles to the surface of the mass.

Other minerals, such as galena and blende (the sulphides of lead and zinc), occur in small balls or nests in some rocks, evidently formed as concretions, and not rolled fragments or pebbles.

This separation of one matter from another, and subsequent assumption of a condition more or less different from that possessed by rocks at the time of their original formation, leads us naturally to consider the next great division of our subject, the metamorphic or transformed rocks.

The mere physical force of pressure, as aqueous rocks after their formation become gradually covered by subsequent accumulations, must produce change in them in the way of consolidation and induration. The pressure may of itself be sufficient in some cases to cause the hitherto incoherent particles of sand or clay to cohere and be compacted into a solid stone. It will, however, be greatly assisted, either by the infiltration of water containing mineral matter in solution, or of pure water dissolving and rearranging the soluble materials which it may find in the rocks.

Heat may, in like manner, modify the effects of pressure, either by its mechanical power of expansion producing pressure in every direction, and subjecting rocks to alternate expansions and contractions according to its own variations, or by setting in action chemical forces of decomposition and recomposition, and thus altering the chemical combinations in the materials of rocks.

Heat may also be joined with water, either raising it to various temperatures or actually converting it into steam, and we may thus get changes produced which neither cold water nor dry heat would be able or likely to effect themselves. It has been stated that it is impossible to maintain the bulb of a thermometer in the boiler of a steamer at very high temperatures, since the glass is dissolved by the chemical action of water heated under pressure. (Sedgwick's Introduction to Synopsis of Classification, &c., 3d Fasciculus, p. 29, note.) Now, it may not unfrequently happen that we may have all the forces of pressure, heat, and the dissolving power of water combined in the interior of the earth.

The presence of water in rocks is known by experience, since no stone is ever quarried which will not part with some water on being dried, either naturally in the air or artificially. Bischof says, that he has observed, on breaking blocks of basalt, "wet patches, like rain drops, upon the fractures, and sometimes quite in the centre of the mass, affording positive evidence of the permeability even of so compact a rock as basalt." He says also, that almost all water contains both carbonic acid, and often a slight proportion of silica (silicic acid) in solution, that the silicates in which the silica is in its soluble modification are decomposed by weak acids, and that those also in which it is in its insoluble modifications are unable to resist the long-continued action of acids.

This gives us the explanation of the brown spots and patches found in many rocks containing silicate of lime, such as basalt and greenstone, and also their brown and weathered surfaces. Along the internal margin of the brown part of basalt and greenstone a mineral acid will almost always cause effervescence, as also along the minute cracks and crevices and pores by which the water gains access to the interior. It is plain that the silicate of lime is converted into carbonate in the first place, and this being removed by subsequent solution from more carbonic acid and washed out, the protoxide of iron left behind is converted into peroxide, and the brown colour produced.

Limestone containing much silica or silicate of alumina, and some protoxide of iron diffused through its mass, is, in a similar way, converted into rotten stone, while pure limestone is wholly dissolved and washed away.

The decomposition of those rocks which do not contain any lime proceeds in the same way, though it is not so easy to detect it by the occurrence of effervescence with acids along the margin of the decomposed part. Feldspar rocks have their silicates of potash, soda, &c., converted first into carbonates and then into bi-carbonates, which are dissolved and washed away. Their decomposed portions are generally white rather than brown, from the absence of iron, though shades or streaks of red and brown occasionally occur, showing its presence in small quantities.

In the examination of these changes, the study of pseudomorphic crystals of minerals is of great importance. A pseudomorph is one mineral occurring in the crystalline form of another. These are either "alteration pseudomorphs," in which the first mineral has been gradually changed into the other, or "displacement pseudomorphs," in which the first mineral having been gradually removed particle by particle, another has gradually, and particle by particle, taken its place. This action is a very important one; for it is precisely that of "petrification," as it is called—that by which organic remains are mineralized, and their external form, and more or less of their internal structure, preserved.

Animals and plants, by means of their fluids, take up and convert into their own substance certain minerals, such as silica, lime, magnesia, soda, potash, phosphorus, carbon, iron, &c. This they do in obedience to the organic forces, those chemico-biological actions, the assemblage of which we call life. When life no longer exists, and its forces cease to act, the substances of animals and plants become obedient to inorganic laws, and their mineral portions are acted on just in the same way that other mineral matters are affected. Wood may either, as we have already seen, lose certain proportions of its constituents and become more and more carbonized; or it may lose the whole of them particle by particle, and as each little molecule is removed, its place may be taken by a little molecule of another substance, as silica, or iron pyrites, and it may thus become entirely silicified or pyritized.

Bones and shells, and other hard parts of animals, consisting mainly of phosphate and carbonate of lime, may in like manner have the proportions or the state of aggregation of their constituents altered more or less completely, or may have their substance gradually but entirely replaced by another substance more or less different from the former.

Bischof combats the opinion that this pseudomorphous and petrificative process is ever the result of dry heat or of sublimation, and shows, with what appears conclusive reasoning, with regard to many substances at all events, that whether it occur in the mass of rocks, or in veins and fissures, it must be the result of water (temperature uncertain) containing some acid, chiefly carbonic acid, in solution in the first place, and afterwards by means of that acid becoming impregnated with the solutions of other minerals.

Some of Bishop's remarks are so very instructive that we do not hesitate to quote several passages at length. "Stain converted a crystal of gypsum into carbonate of lime by leaving it for several weeks in contact with a solution of carbonate of soda, at a temperature of 125° F. The sulphuric acid of the gypsum uniting with the soda to form sulphate of soda, which was dissolved and carried away by the water, and the lime uniting with the carbonic acid." All the strain upon the curved surfaces of the crystal were perfectly retained, as well as the cleavage in the direction of the T-planes. In these artificial pseudomorphous processes, the form of the original substance is retained only under certain conditions, the most essential being slow action; and the same holds good in nature. If these conditions are not fulfilled, the original form is lost.

"In the analysis of a mineral in which changes have already commenced, especially by the addition of new constituents in very minute quantities, it is not unlikely that they may be considered accidental and deducted. Since, however, alterations seldom take place merely by addition, but more frequently by loss of constituents, it is likewise requisite that the quantities lost should be added to the analytical results."

There are sufficient grounds for considering andalusite to be a pure silicate of alumina, although previous analyses have pointed out, besides these two essential constituents, potash, lime, magnesia, oxides of iron, and manganese and water. Andalusite is converted into mica, in which change a part of the alumina is removed; potash, magnesia, and peroxide of iron, being introduced into its place. One of these bases is always found in andalusite, sometimes several of them together; and it may therefore be inferred that this mineral, as usually met with, is already in a state of incipient alteration. No other alteration of andalusite is known besides that into mica, except that into steatite. The latter change presupposes not only a partial but a complete disappearance of the alumina, and its replacement by magnesia. These examples will suffice to show the importance of the minute quantities of substances present in minerals, and generally considered as accidental. These substances, which are troublesome to the chemist, because he cannot introduce them into the chemical formulae, acquire significance when compared with the constituents of the pseudomorphs, resulting from the alteration of the mineral in question. They are no longer appear as accidental, but indicate the transition of one mineral into another lay before us clearly the greater part of the conversion process.

"It is possible that several changes may frequently have taken place before the last product was formed. In the alterations of complex minerals, especially silicates containing several bases, there are, certainly, transitions in most cases, and sometimes a long series. Thus Cordierite is the starting point of a whole series of alterations, finally ending with Mica; while Prasolite, Chlorophyllite, Bonsdorite, Esmarkite, Weissite, Prasolite, Gigantolite, and Pinite, are remains of Cordierite in pseudomorphic conditions. Inasmuch as the minerals between Cordierite and Mica are only transition products, they cannot be regarded as individual species."

"As petrifactions are important and in many cases indispensable aids in recognizing the sedimentary formations, so likewise pseudomorphs are important, and frequently the only means of tracing the processes of alteration and displacement which have taken place and are still going on in the mineral kingdom."

"Pseudomorphs furnish us with a kind of knowledge which we have no opportunity of deriving from any other source. It will scarcely ever be possible to convert augite, olivine, or hornblende, &c., into serpentine in our laboratory. But when we find serpentine in the forms of these minerals, this fact is a sufficient evidence that such a conversion can take place; and if in any given instance there are geognostic reasons for the opinion that one or other of these minerals, or even several together, have furnished the materials for the formation of serpentine, there is a high degree of probability that such a change has actually taken place.

"If a crystalline mineral can, under certain conditions, be converted into another, whether with or without retention of form, then the same mineral in an amorphous state would certainly suffer the same change when placed in the same circumstances." From this he shows that amorphous masses of serpentine may be formed from amorphous masses of augite, &c., and also that in some instances the original form of a crystalline mineral may be destroyed together with its substance, and the new mineral occur in its own crystalline form. He concludes the subject thus:

"The importance of the pseudomorphous processes, and the error of those who regard them as having but little connection with the changes of rocks, is sufficiently shown by the total disappearance of previously existing substances in veins. I consider that the entire removal of flase and calc spar from a whole series of veins, and the introduction of an equal quantity of quartz in their place, is a matter of no importance. To what enormous spaces of time do we come when we reflect upon the periods during which the flase and calc spar were introduced into these cavities, and then periods during which they were again removed by water, and quartz substituted in their place! Yet this happened after the formation of the rocks in which these fissures occur. If we imagine similar processes to have taken place in the rocks themselves, and extending over not only both these periods, but the entire space of time since their formation, we shall be compelled to admit that inconceivably stupendous changes have taken place. After such considerations, the conversion of extensive masses of rock by the action of water alone into steatite, talc, serpentine, kaolin, &c., cannot appear in the slightest degree remote." (Bischof, chap. ii.)

If we allow so large an amount of metamorphic action to the infiltration of water, it becomes no longer difficult to understand the conversion of limestone into dolomite, subsequently to the deposition of the original carbonate of lime. Such cases as those described by Von Buch, and more recently by Mr Andrew Wyley, in the journal of the Geological Society of Dublin (vol. vi., part 2), in his paper on the Dolomitic Rocks of Kilkenny, where dolomite is found traversing ordinary limestones in dyke-like masses running through a great number of beds in a straight line across the country, becoming explicable on the supposition of springs of water containing much carbonic acid and magnesia rising up through fissures, and the consequent solution of some of the carbonate of lime and its replacement by carbonate of magnesia.

If, again, such great changes as those just alluded to may be expected to result from the simple action of water, we may reasonably conclude still greater to be the consequence of the action of water combined with a high temperature, or of a still more intense heat, which first converts into steam the water contained in rocks, and effects great changes perhaps, or, at all events, prepares the way for great changes by that agent, and then proceeds to act upon the minerals contained in rocks with its own powers. We have already seen that some sandstones and gritstones may have probably been cemented by silica held in solution, either in the water in which they were deposited, or in that which subsequently gained access to them. We know that hot water can contain at least a tenth more silica in solution than cold water. If, therefore, a sandstone became penetrated by hot water, or still more by steam, a portion of the silica of which each grain was composed might be dissolved, and as the water ultimately evaporated, this silica would be redeposited, and act as a siliceous cement to the mass. We should thus have a quartz rock or quartzite produced.

It would appear, however, that dry heat alone is able, under favourable conditions, to produce this effect, since the sandstones that have been used as the bottoms of iron furnaces are, in some cases, altered into a kind of quartz rock. It is true that bases, calculated to act as a flux to the quartz, may have gained access to the sandstone in the latter instance, but then they may, on the other hand, have been present in sufficient quantity for that purpose in many sandstones that have been naturally altered into quartz rock.

While we give full allowance to the importance and magnitude of the metamorphic effects produced by water at whatever temperature, there are yet still greater and more general changes, which we must believe can only have been effected by the action of heat, too great to allow of the presence of water. When we see whole mountain ranges, and whole districts of country, consisting of rocks that have more or less analogy in structure and constitution to rocks known to be of igneous origin, we cannot help feeling convinced that igneous action must in some way have been concerned in their production.

When we find that these rocks have every gradation, from such as might have been once molten, into rocks which we know to have been mechanically deposited under water, we are compelled to conclude with Lyell that these rocks are altered or metamorphosed by heat from their original aqueous and mechanical formation into a state more or less nearly approaching true igneous rocks.

Our belief in the truth of this metamorphism becomes certainty when we see these rocks always occurring on the flanks of masses of granite, and examine a district (such as Wicklow and Wexford) where both large and small masses of granite appear, and find these metamorphic rocks, not only always accompanying the granite, but occurring nowhere else except in the neighbourhood of granite or granitic rocks, and their extent always proportioned to the size and extent of the particular granite mass they mantle round.

It is by no means intended to assert that the neighbourhood of granite or igneous rock is the only source of heat from which this metamorphosis can arise. Should any mass of rock, capable of alteration, be so deeply buried in the earth as to be brought within the reach of any centre of heat whatever, the same effect would result; and it is quite possible that a far greater intensity and wider range of heat may be thus reached, than could proceed from the mere intrusion of a more or less isolated mass of igneous matter into spaces which were naturally of a lower temperature. But as an intrusive mass of granite must be a source of great heat, and as the metamorphic effects in question are found always to accompany it, we are obliged to look upon heat as the cause of the effect.

This effect of intense heat may doubtless be variously modified by the previous presence or absence of water, and by the various mixtures of mineral matters occurring in the different rocks before alteration.

The very general appearance of mica, either in distinct flakes or crystals, or as a mere glaze upon the surfaces of laminae, may perhaps be explained by the very various composition of the different varieties of mica, and the consequent number of sources and combinations from which micaceous minerals could be derived. Mr Sorby has shown by the help of the microscope that many ordinary clay-slates are in reality made up of minute mica flakes. Dr W. K. Sullivan also has remarked to us the possibility of several different minerals, or at least many chemical combinations, putting on the micaceous form as a consequence of peculiarity in physical structure rather than of identity in chemical composition.

The metamorphic development of mica, then, offers no difficulties; and we may perhaps suppose that in mica schist, where there are alternate layers of mica and quartz, this development took place in such a way that the basic substances segregated themselves into alternate layers, leaving the silica of the intermediate layers free; these layers being determined by the original lamination or sedimentary layers of the mass, except where that mass was very homogeneous, or greatly affected by "transverse cleavage."

In gneiss, where we have the triple alternation of quartz, feldspar, and mica, a similar action, similarly directed, must be supposed to have occurred under the modifying influence of a different composition in the original rock.

We shall have occasion, under the head of Petrology, to recur to this subject in describing the "cleavage" and "foliation" of the metamorphic rocks. "Cleavage" is, indeed, a purely petrological structure, whatever may have been its origin, since it rarely, and only to a slight extent, produces any lithological change in a rock beyond that of simple induration. A highly indurated shale has no lithological difference from a true clay slate, it being often impossible, from an inspection of a mere hand specimen, to say whether it be one or the other.

**DESCRIPTION OF THE METAMORPHIC ROCKS.**

The metamorphic rocks may be divided into two sub-groups, those in which the original mineral structure is still recognisable—the particles, however they may have altered their form and state, not having entered into new combinations—and those where such new combinations have been produced.

The former sub-group will accordingly consist of arenaceous, argillaceous, and calcareous rocks, while the members of the latter have a general similarity of structure and composition which enables us to speak of them under one general term, such as the schistose rocks.

**Metamorphosed Arenaceous Rocks.**

60. Quartz Rock or Quartzite is a compact, fine-grained, but distinctly granular rock, very hard, frequently brittle, and often so divided by joints as to split in all directions into small angular but more or less cuboidal fragments. Its colours are generally some shade of yellow, passing occasionally into red, and at other times into green. When examined with a lens it may be seen to be made of grains, which appear sometimes as if they had been slightly fused together at their edges or surfaces, and sometimes as if imbedded in a purely siliceous cement. This cementation or semi-fusion of the grains shows at once that it is a sandstone which has been altered and indurated by the action either of heat alone or of heat and water. It has either been baked or steam-boiled.

**Metamorphosed Argillaceous Rocks.**

61. Clay Slate is a fine-grained fissile rock, differing from shale in being invariably highly indurated, and splitting into plates that are altogether independent of the original lamination or bedding of the rock, and frequently cross it at all angles. This fissile structure or "cleavage" is a superinduced or metamorphic one. The original bedding or lamination of the rock may frequently be traced, even in hand specimens, by means of parallel lines or bands of different colour and texture traversing the slate. These bands are called by Professor Sedgwick the "stripe" of the slate.

Clay slate is generally of a dull blue, gray, green, or black colour, sometimes "striped," sometimes irregularly mottled.

**Metamorphosed Calcareous Rocks.**

62. Altered or Crystalline Limestone.—This was for-

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1 See pages, under the head of Petrology, remarks on the production of mica-schist and gneiss on the flanks of the granite of Wicklow, &c.

VOL. XV. The separation into layers, or "foliation" of mica schist, sometimes coincides with the original bedding of the mass, and sometimes is independent of it. In the latter case, it may in some cases have taken the direction of a previously existing "cleavage." (Prof. Ramsay, Geological Journal, vol. ix., p. 172.)

Instead of mica, other minerals are sometimes found, such as chlorite or talc, when the rock would be called chloritic schist, or talcose schist.

Hornblende schist, again occurs, though we believe, in this case, the whole mass consists of flakes of that mineral without any alternation of quartzose layers. The same remark holds good with respect to the rarer rock called actinolite schist. As far, indeed, as our own observation goes, we should doubt the existence of these rocks in any other form than as the result of a partial metamorphosis of some hornblende "ash," or of some other mechanically-formed rock, derived from the wear and tear of a greenstone or a syenite.

65. Gneiss is probably of all others the most completely metamorphosed rock that retains any mark of its original mechanical structure.

Some gneiss can only be distinguished from granite by the regular arrangement of its component crystalline particles in a certain parallelism, so as to give it a slightly schistose structure, or "grain," as it is called by Professor Sedgwick. Other varieties of gneiss, again, can only be separated from mica schist by the occasional occurrence of little plates of feldspar in addition to the layers of mica and quartz. In hand specimens, indeed, it is often very difficult to draw any sharp line of separation between mica schist and gneiss, the more fissile specimens being called mica schist, while the firmer ones would be called gneiss. Even in the field they are often so blended together, and alternate with each other so frequently, that their separation is impossible. There is therefore almost every gradation from dull clay-slate through glossy and so-called talcose slate into mica schist and gneiss, and thus into actual granite.

Gneiss might, indeed, in its purest and most typical form, be termed schistose granite, consisting, like granite, of feldspar, mica, and quartz, but having those minerals arranged in layers or plates, rather than in a confused aggregation of crystals. In speaking of it as schistose granite, however, we must never forget that true gneiss was never really a granite, with a peculiar laminated structure, but that it was originally a laminated mechanically-formed rock—a sandstone more or less argillaceous, containing, indeed, the elements of quartz, feldspar, and mica, but not exhibiting any more appearance of those minerals at its first deposition than is exhibited by any of the ordinary unaltered sandstones with which we are familiar. We by no means intend, however, to assert that all sandstones could be converted into gneiss, for it is obvious that purely siliceous sandstones could not, but purely siliceous sandstones are much more rare than is often supposed. The great mass of sandstones and of clays do contain the elements of feldspar and mica as well as quartz—that is to say, they contain alumina, iron, potash, soda, magnesia, &c., as well as silica.

We must also never forget that the extreme term of metamorphism by heat is actual fusion and reduction into the state of an igneous rock, and that it is possible therefore that some igneous rocks, nay, even some granites, may be metamorphosed rocks—aqueous rocks that have been completely melted down again. If we look upon all aqueous rocks as in some shape or other derivative rocks,—and this is a conclusion from which we cannot escape,—we must regard them as either mediately or immediately derived from igneous rocks. With regard to the mechanically-formed aqueous rocks this is obviously true, because if we trace to

The Schistose Metamorphic Rocks.

The term "schist" is used here in a restricted sense, as applicable to the fissile structure of "foliated" rocks.

"Foliation" is a term applied by Mr. Darwin to those rocks which have had such a subsequent structure given to them as to split into plates of different mineral matter, either with the bedding or across it. "Cleavage" indefinitely splits a rock, either with the beds or across them, without altering its mineral character, and thus produces "slate."

"Lamination" will then be the remaining term applicable to "slate," and signifying the splitting of a rock into the original layers of deposition.

When, therefore, we wish to be precise, we can speak of the foliation of schist, the cleavage of slate, and the lamination of shale.

64. Mica schist consists of alternate layers of mica and quartz, the mica generally consisting of a number of small flakes firmly compacted together, and the quartz more or less nearly resembling vein quartz. Many mica schists, however, contain comparatively little quartz, and seem scarcely to differ from clay slate or shale, except in the shining surfaces of their plates or folia.

Many mica schists have a minutely corrugated or crumpled structure, the layers being bent into sharp vandykes of one, two, or more inches in height and width. Others, however, are quite smooth and straight.

Now Sir William Logan.

The term "foliated," however, as applied to schistose rocks, such as mica schist, and distinguished from "cleaved" as applied to slate, was first suggested by Professor Sedgwick in his paper on the "Structure of large Mineral Masses." (Geological Transactions, vol. iii., pp. 479 and 480.) their original source the silica and alumina, the quartz, the feldspar, and the mica of which they are composed, we must eventually arrive at some igneous, most probably some granitic rock as their parent.

But even as regards the lime and the soda and magnesia of all the chemically and organically-formed aqueous rocks (setting aside the carbonaceous rocks), we are compelled to suppose that the water first derived those minerals from the decomposition of such igneous rocks as contained them. The carbonates of lime and magnesia, and the sulphates of lime, must have acquired their bases primarily from the decomposition of the silicates of lime and magnesia, which are to be found in the igneous rocks; carbon itself being the only element which does not seem primarily derivable from igneous rocks. Speaking generally, then, it need not surprise us to find materials that had once been fused reduced again to that condition. It is true, that in our purest sandstones and clays the matters that once acted as a flux to the silica and alumina may have been washed out and removed more or less completely from their former combinations; but these pure deposits of silica or silicate of alumina are, as just now said, comparatively rare and in small quantity, and if the rocks around them and inclosing them were once to be remelted, they would soon become mixed up and mingled with the rest, and reduced to the same condition.

There can therefore be nothing either unphilosophical or improbable in regarding, with Sir C. Lyell, the whole crust of our globe as consisting of materials passing through an endless cycle of mutations—existing at one time as igneous rocks; then gradually decomposed, broken up, separated out, sorted, and deposited as aqueous rocks, whether chemical, mechanical, or organic; at a subsequent period metamorphosed; and ultimately reabsorbed into igneous rocks.

In this view, the most highly metamorphosed rocks would be those most nearly hovering upon the brink of reabsorption; and gneiss accordingly on the point of passing into granite, and in some cases almost undistinguishable from it.

One thing is quite certain, that many rocks which are now undistinguishable from true igneous rocks, may have been formed by a comparatively slight metamorphism of "ashes," or other mechanical accumulations of materials derived directly from igneous rock, and subsequently brought within the influence of heat. It is probable that many amygdaloids may be altered tufts or ashes, and possible perhaps that some clinkstones, whether volcanic or trappean, may have a like origin. Some felsstones, again, may be but baked and slightly altered feldspathic ash.

Some real and originally-formed igneous rocks may in like manner undergo metamorphoses, more or less complex. Some felsstone or greenstone porphyries, for instance, may have acquired their porphyritic structure by long-continued and comparatively gentle heat, acting on previously compact trap rocks. The same comparatively slight action of heat may have caused many once compact or porphyritic igneous rocks to have become completely crystalline, and possibly may in some cases have generated new combinations, and produced mineral forms that did not exist in the original rock. Trappean rocks may thus have become granitic. These possibilities should be borne in mind when we are endeavouring to explain phenomena that otherwise are often difficult to understand.

It will, perhaps, be useful if we give here the foregoing classification of rocks in a tabular form:

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**IGNEOUS ROCKS**

**VOLCANIC**

Essentially Feldspathic: - Trachyte - Trachytic Porphyry - Pearlstone - Andesite - Clinkstone - Obsidian - Pumice - Tuff

Siliceo-feldspathic: - Felstone - Pitchstone - Clinkstone - Feldspar Porphyry - Feldspathic Ash

**TRAPPEAN**

Feldspar and Hornblende, &c. - Greenstone or Diorite - Melaphyre - Diabase - Dacro - Hypersthene - Aphanite - Serpentine - &c., &c.

**GRANITIC OR SUPER-SILICATED ROCKS**

Quarzo-feldspathic: - Pegmatite - Elvanite - Buriite

Quarzo-feldspathic with Hornblende or Mica, &c. - Syenite - Protagone - Granite

**AQUEOUS ROCKS**

**MECHANICALLY-FORMED**

Gravel or Rubble - Conglomerate or Pudding-stone and Breccia - Sand - Sandstone and Gritstone, and their varieties - Clay and Mud - Clunch - Loam - Marl - Shale or Slaty Clay

**CHEMICALLY-FORMED**

Calcaceous: - Stalactite and Stalagmite, Travertine, &c. - Some Dolomites - Sinter - Gypsum - Rock Salt

Siliceous: - Flint and Chert

Organically-Derived: - Limestone and its varieties, compact, crystalline, chalky, oolitic, pisolithic, some magnesian, &c. - Coal - Anthracite - Graphite

**AERIAL OR AEOLIAN ROCKS**

Blown Sand on coasts - Sandhills of deserts - Calcareous Sands compacted by rain, &c. - Debris at foot of cliffs - Volcanic Ashes, &c., falling on land - Soil

**METAMORPHIC ROCKS**

**THOSE IN WHICH THE ORIGINAL STRUCTURE IS STILL APPARENT**

Arenaceous: - Quartzite or Quartz rock - Clay Slate

Argillaceous: - Primary, Crystalline, or Saccharine Limestone, or Statuary Marble - Serpentinous Limestone, Verde Antique, &c. - Some Dolomites

**THOSE IN WHICH THE ORIGINAL STRUCTURE IS MORE OR LESS COMPLETELY OBSCURED OR obliterated**

Mica Schist - Chlorite do. - Talc do. - Hornblende do., &c. - Gneiss Sect. II.—Petrology.

By that division of Geognosy here called Petrology, we may understand the study of rock masses; that is to say, the examination of those characters, structures, and accidents of rocks which can only be studied on the large scale, and only be observed in "the field." This study will comprise the modes of stratification, of separation by divisional planes, those of fracture and disturbance, and those of denudation, as well as the composition of groups or "formations," and the relations of igneous to aqueous rocks.

Chap. V.—Petrology of the Aqueous Rocks.

I.—Lamination and Stratification.

The lamination and stratification of the aqueous rocks is the very foundation of geology,—that on which all the more important deductions of the science are based. It is therefore necessary to describe these structures in some detail.

We have already mentioned the very fine laminae (plates or layers) of which some beds of shale are made up. Each of these little layers of earthy matter is obviously the result of a separate act of deposition. The whole bed of shale being formed by the gradual settlement of fine sediment, film after film, upon the bottom of some tranquil or very slowly moving water, we may suppose this sediment to have been carried into the water by successive tides bringing matter from some neighbouring shore, by frequent or periodical floods of some river, by the gradual action of some current, or any other agent by which we could imagine fresh materials to have been transported at different intervals into the water. Or we may perhaps suppose that the supply being continuous, and the water more or less turbid throughout, the act of settlement took place at intervals by little successive fits and starts. Whatever may have been the exact nature of the action, it was clearly a gradual, and not a sudden one; and some time must be allowed for the deposition of a bed even one foot thick, when we find it, as we often do, made up of distinct laminae, fifty or a hundred of which do not exceed an inch in thickness.

Still, although some time was required, and although the acts of deposition were distinct, yet they were not so widely separated in time as to allow of any great consolidation of one layer before the next was deposited upon it.

The whole set of laminae were made to cohere together, so as ultimately to form one bed, which may be quarried and lifted in single blocks.

Now the planes of stratification differ in this respect from the planes of lamination, that they mark a total want of coherence between two contiguous layers of rock. It would be impossible to get a block consisting of a part of two beds; there would obviously be two blocks.

It follows from these facts, that as the coherence of the laminae of a bed is the result of the comparative shortness of the intervals between their deposition, so the want of coherence between one bed and another is the result of the length of the interval between the deposition of the beds. Each bed had time to become consolidated, to a greater or less extent, before the next was deposited upon it, so that the latter could not at all coalesce with the former. The planes of stratification, then, mark an interruption in the act of deposition, a pause during which nothing was deposited; the duration of that pause being very considerably longer than that of the intervals between the successive laminae.

Laminae or layers, then, are the parts of which a bed is made up. Strata or beds are the distinct sheets or wide tabular masses of aqueous rock which are completely and naturally separated from each other. The planes of lamination often refer only to the direction in which the laminae are arranged, whether the laminae are separable or not. The planes of stratification are actual planes of separation between one bed and another.

If we are at a loss to estimate the length of the interval between the deposition of the successive laminae of a bed, still less have we in general the means of calculating the time which elapsed between the formation of one bed and another. When two or more beds are of precisely similar character, as two beds of the same kind of shale or sandstone, we should naturally be led to suppose that the interval between bed and bed was not indefinitely greater than that between lamina and lamina. If we assigned hours to the one, weeks to the other; if days to the one, weeks to the other; and so on. Still we should have no certain grounds to go on, and the interval between bed and bed might be years or centuries for anything we could, in the majority of instances, show to the contrary. When, moreover, the two beds were of totally different characters, as, for instance, where a bed of sandstone or limestone rested on a bed of shale, or vice versa, we should generally be right in allowing a larger interval between their deposition than where the beds were similar. Some time must be required for a change to take place in the conditions of the neighbourhood. In the case of a bed of sandstone, destitute of all argillaceous matter, resting on a bed of shales, we should be obliged to suppose some alteration in the strength or direction of the currents, so that all the finer matter was swept away, and only the coarser or heavier deposited. In the case of a shale resting on a sandstone we should suppose that the current had diminished in velocity compared with that formerly acting. In either case the current might come from a new quarter where only one kind of material was to be got.

The same current of water, charged with a mixture of gravel, sand, and mud, and having strength enough to carry it all on together, will, as its strength lessens, sort and separate the materials from each other, depositing them in the order of their coarseness, the pebbles first, chiefly by themselves, next the sand by itself, and lastly, the mud by itself. Three different kinds of rock, then, may be deposited at the same time by the same current; but in order that either sand or gravel may be thrown down at a subsequent period on the top of the mud, a fresh current either of greater velocity or from a nearer source will be required, while an interval will be necessary for the mud to consolidate so far as either not to be removed by the new current, or not to allow the fresh pebbles or sand to sink into it.

In the case of a limestone occurring either on shale or sandstone we are still more forcibly compelled to the supposition of a great change of conditions. If the limestone be a pure carbonate of lime without much admixture of mechanical detritus, it is obvious either that all currents had ceased in the water which had previously deposited the sandstone or the shale, or else that they were no longer able to get any earthy matter and transport it to that place. If, indeed, as seems necessary in the case of all marine limestones, we assign an organic origin to this rock, we are compelled to allow a period prior to its production sufficient for the animals from which it is derived to grow and to secrete their solid materials from the adjacent water.

It is possible, indeed, in some cases, by the aid of the remains of animals and plants found fossil in the rocks, to arrive at something like a rough approximation to the time which has elapsed between the formation of successive beds. There are cases, for instance, in which we find

1 Just as was previously shown for mud of different degrees of coarseness in Mr. Habbage's observations. on the surface of a bed of limestone the roots or attachments of a particular class of marine animals, called encrinites, which when alive were fixed to the rock by a solid calcareous base. These attachments belong to animals of all ages, and are in great numbers; and in a bed of clay or shale which rests immediately on the limestone, there are found a multitude of the remains of the upper portions of these animals, likewise of all sizes and ages. Now it is plain that in this case, after the limestone was formed and consolidated, there was an interval during which the sea was quite clear and free from sediment, and therefore well adapted for the growth of these animals; that they, after a time, settled accordingly on the hard limestone at the bottom of the sea, and grew and flourished there for a sufficient period to allow of successive generations arriving at maturity undisturbed, before the time when a quantity of mud, having been carried into the water, was deposited upon them, and killed them, and at the same time buried their remains. Here, then, we have an interval of many years, if not of centuries, between the formation of two beds of clay and limestone which rest directly one upon the other. (Buckland's Bridgewater Treatise, vol. i., p. 429.)

Many instances similar to this occur to the geologist when pursuing his investigations, although not often admitting of such clear illustration and description. (See Lyell's Elements for other examples.)

On the other hand, we have instances of fossil trees passing through several beds of sandstone, in such a way as to show that the whole number of beds were accumulated after the tree had sunk, and before it had time to rot entirely away. These trees evidently became waterlogged, and sunk to the bottom, where they rested in an inclined position, anchored by their roots, while successive deposits of sand were accumulated round them. But a tree thus wholly buried in water will last many years before it is entirely decomposed, so that it might very well have become enclosed in several beds of sandstone, especially when we recollect that it forms an obstacle to the currents flowing by it, and checks their force, and thus causes the deposition of sand around it more rapidly than would otherwise take place. Still, whatever number of years we assign to the accumulation of the whole mass of sandstone, we cannot in this case suppose any great interval to have elapsed between the deposition of one bed and that which rests upon it.

It is possible in some cases, even without the aid of organic remains, to discover that the interval between two adjacent beds was a comparatively long one. For instance, we not unfrequently find that two beds, which in one place are contiguous, do in another place let in one, two, or more separate beds between them, as in fig. 4. It is obvious that if we observed the beds \(a, e\) at the spot marked \(A\), we should only suppose an ordinary interval to have elapsed between the times of their deposition; while on tracing the beds to \(B\), we are compelled to enlarge that space of time sufficiently to allow for the formation of the beds \(b, c,\) and \(d\), and the intervals between them. It appears, then, that while we are able to assign a sort of rough limit to the time required for the deposition of one bed, composed of a number of laminae, we are rarely able to assign any approximate limit to the time required for the formation of a number of beds. Not only have we to multiply the first period by the number of the beds, but to allow for an equal number of intercalated intervals, of altogether uncertain duration, to represent the pauses that occurred between the formation of each two contiguous beds.

In some cases, if not in most, these intercalated intervals would be probably much greater than the periods of deposition, because we cannot very well imagine any set of circumstances that can keep up a continuous or rapid deposition of earthy matter, whether chemical or mechanical, for a very long and indefinite period of time, in any one particular locality. All we know, or can conceive, of the accumulation of earthy matters in the seas or lakes of the present day points to a discontinuous and interrupted action, a bed of sand being formed here, a patch of mud deposited there, a bank of pebbles accumulated in one place, a bed of oysters or other shells growing in another, so that the bottom of the sea becomes gradually covered by several unconnected and partial patches of deposition of different kinds, lying side by side. All our experience shows that for any great thickness or vertical succession of beds like these to be formed, in other words,—for the depth of water to be materially diminished (except in narrow bays and inlets)—a great length of time is required.

The soundings in shallow seas, such as those round the British islands, do not alter very rapidly, though they do alter; and the bottom at one period is found to be very various, "mud," "sand," "sand and shells," "small stones," and similar terms, being scattered over the charts. These "bottoms" remain constant for a sufficient number of years to be used as a guide in navigation. In other words, great intervals commonly occur between the deposition of very different deposits at any particular spot on the bottom of the sea.

Moreover, if we take the whole earth generally, and limit ourselves to the consideration of any given instant of time, we must look upon the deposition of mineral matter as the exception, not the rule. Of many hundred thousand square miles of sea, only one perhaps is receiving, at any given instant, the accession of any mineral matter on to its bed. The next successive depositions may either be in adjacent or in widely separated localities; and a vast number of these partial and detached acts of formation will be required before the whole of any particular area will be covered with one or more beds of rock. In reasoning on the methods of production that have been concerned in the formation of our great series of stratified rocks, we are compelled to suppose a similar gradual, partial, and interrupted action to have taken place.

When we rise from the consideration of single beds to that of groups of beds, we find instances, on a still larger scale, of intervals having taken place in the deposition of rocks which at first appear perfectly continuous. Mr Prestwich, in his paper on the "Correlation of the Eocene Tertiaries of England, France, and Belgium" (Journal of the Geological Society, August 1855), shows that on examining the rocks called tertiary above the chalk in France, they appear to have a regular continuous sequence of beds of sand and clay, &c., in which there is no sign of any interval having happened, while in reality a group of the English tertiaries, known as the London clay, having a thickness of 400 feet near London, was deposited in an interval between the formation of two of the French beds. We cannot conceive the London clay to have required less than some thousands of years for its formation, and it may more probably have been many tens of thousands, during which interval no corresponding deposition was taking place over parts of the north of France, though deposition did take place both before and after this period, equally in the seas which covered what is now France and what is now England.

Such instances compel us to raise our estimate of the time required for the formation of a great series of stratified rocks to a perfectly illimitable extent.

These considerations, although they may appear somewhat speculative, are important, as leading us to a true interpretation of many of the appearances which the geologist meets with in his course of observation; and the student will do well if he accustom himself to look upon single beds of shale, &c., as the possible representative of a century or two, and upon small groups of beds as the product of thousands, or perhaps even millions of years.

II.—EXTENT AND TERMINATION OF BEDS.

In fig. 4 it is shown that, of a set of five beds at B, only two continue so far as A, the other three having thinned out and come to an end before reaching that part. This leads us to another conclusion respecting beds of stratified rock, namely, that although sometimes very widely spread, they are not of indefinite extent, but must end somewhere. This ending is generally a gradual one, the bed becoming thinner and thinner, till at last it disappears. Sometimes, however, though rarely, the termination is much more abrupt. Whether we reason from our own experience, or from the nature of the case, we should never be led to believe that the deposition of sediment in water, whether it be a chemical or a mechanical one, could, except in very rare instances, be coextensive with the whole water. With respect to the sea, we cannot conceive any natural causes which could produce such an universal and simultaneous deposition, and should never expect to find a marine bed, the area of which at all approached in extent that of the water in which it was formed. The wonder perhaps is, that single beds sometimes extend over such very wide areas as we really find them to occupy.

The extent of single beds is most certainly ascertained in coal mining, in which the horizontal (or lateral) extension of beds is followed. Particular beds of coal, or of shale, or other rock having remarkable and recognisable characters, are sometimes known to spread throughout a whole district. For instance, in South Staffordshire a bed of smooth black shale, a little below the thick or ten-yard coal, is known as the "table batt." It has a thickness of from two to four feet, and extends over all the greater portion of the South Staffordshire coal field—places where it is known being ten or twelve miles apart from each other in straight lines and in different directions. Its original extension was probably much greater, since the beds now disappear in one direction by "cropping out," and are buried in others at too great a depth to be followed. Known beds of coal, with a particular designation, such as "Heathen coal," extend over still wider areas, and similar facts occur abundantly in most coal fields.

When from a single thin bed we come to the examination of a group of a few beds, the instances of mineral identity over very wide areas become still more frequent. This is especially observable when the group of beds is of a character quite different from the larger mass of rocks in which they lie; provided that difference points to a state of greater tranquillity or quietness of action, as would a bed of clay occurring in a group of sandstone beds, or a bed of limestone or coal occurring in others having a purely mechanical origin.

On the other hand, some beds, even of a considerable thickness, have a remarkably small extension, being mere cakes, thick in the middle, and thinning out rapidly in every direction. This happens sometimes with all kinds of aqueous rocks; but is the more usual characteristic of the coarser mechanically-formed rocks, being more common in sandstones than in clays and shales, and more frequent in conglomerates than in sandstones.

Beds of sandstone in the coal districts are sometimes found to thicken or thin out very rapidly. This is easily observable where sandstone beds are known to the colliers by specific names, and where the coal pits are near together. The miners are occasionally thrown out in their calculations as to the depth at which particular coals will be found by these irregularities, which are sometimes so great and rapid, as to be called "faults" by men not accustomed to precision in the terms they use. Such an instance occurs near Wednesbury in South Staffordshire, where a bed of sandstone, known by the name of the "New Mine-rock," thickens out from 9 feet to 78 feet in the course of a few yards' horizontal distance. In other parts of the district this sandstone varies from 15 to 60 feet, and in some places is entirely wanting.

In examining sandstones and conglomerates, the conglomerates or old gravel beds are often found to be very partial and irregular, forming steep-sided banks and mounds enveloped in sand.

In these cases, although it was obviously a work of time for the pebbles to have been worn and ground down from their original large and angular condition to their present small rounded form, and although we may very well suppose them to have been washed about from place to place, and thus to have eventually travelled far from their original site, yet their final deposition in the place where we now find them was probably a rather rapid and sudden action.

Conglomerates, then, may be quoted as examples either of the length of time required for their formation, or of its shortness, according as we look to the preparation of their materials or the actual deposition of them. This remark holds good, too, with respect to all other coarse mechanically-formed rocks.

III.—IRREGULAR AND OBLIQUE LAMINATION AND STRATIFICATION.

In shales the laminae are remarkably thin and regular, all parallel to each other, and parallel also to the planes of In many fine-grained, and in some coarse-grained sandstones, this regularity and parallelism likewise prevails. In other sandstones, however, great irregularity is observable in the laminae of which the beds are made up, the layers of different-colored or different-sized grains being oblique to the planes of stratification, and various sets of layers lying sometimes at various angles and inclining in different directions in the same bed, as in fig. 5.

This structure is a proof of frequent change of direction, and probably of strength, in the currents which brought the sand into the water. If we suppose a current of water running over a surface which ends in a slope, as at \(a\), in fig. 6, it is clear that any sand which is being drifted along the bottom from \(b\) will, on reaching \(a\), roll down into the comparatively still water of the deeper part, and remain there probably undisturbed. Layer after layer of sand may thus be deposited in an inclined position according to the slope of the bank.\(^1\) On the other hand, if any obstacle arrests the sand which is being drifted along the bottom of any water, some of it will be piled up into a heap, and a bank will be then formed having laminae more or less inclined. If the current shifts its direction, another bank may be formed with its laminae inclined at a different angle or in a different direction. Moreover, after one bank has been formed, a subsequent change in the velocity or the direction of the moving water may cut off and remove a portion of it, or excavate a channel through it, and this hollow or fresh surface may be again filled up or covered over by layers having a different form from the first. In this way water subject to changes of current, especially shallow water full of eddies, will throw down or heap up materials in a very confused and irregular manner.

It is a modification of this action probably which has produced what are called "rolls," "swells, or 'horses' backs," in the coal measures, and probably in other rocks where they remain less noticed.

A long ridge, and sometimes one or two parallel ridges, of clay or shale are occasionally found rising from the floor through one or more beds of coal, "cutting them out," for a certain distance, to use the miners' terms. The crest of such a ridge is sometimes 8 feet above the floor of the coal, with a very gentle inclination on either side, the beds of coal ending smoothly and gradually against it. (See Records of School of Mines, vol. i., p. 2.) Its formation was obviously anterior to that of the coals which it "cuts out;" those coals and the "swell" itself being regularly covered either by a higher bed of coal, or by the "roof" of the seam,

\(^1\) A very pretty little machine has been invented by Mr Sorby for producing this oblique lamination. Sand poured into a small trough is carried forwards by means of a screw, and falling down into a narrow space between a board and a sheet of glass, arranges itself in inclined layers, according to the rapidity with which the screw is worked and the angle at which the instrument is held.

without any interruption or disturbance. The swells are sometimes 200 or 300 yards long, and 10 or 12 yards wide at the base. (See fig. 7.)

IV.—CURRENT MARK OR RIPPLE.

Another effect of current is to produce a "ripple" or "current mark" on the surface of a bed of sandstone or sandy shale. This rippled surface is exactly the same as that which is seen on the sands of the sea-shore when left dry by the tide, and which may occasionally be seen at the bottom of any clear water where a current is moving over a sandy surface. It may be observed also sometimes on sand-hills on dry land, being produced by the drifting action of the wind. Either wind or water, as they roll before them the little grains of sand, tend to pile them into small ridges, which are perpetually advancing one on the other, in consequence of the little grains of sand being successively pushed up the windward or weather side of the ridge, and then rolling over and resting on the lee or sheltered side.

It is produced on the sea-beach, not in consequence of the ripple of the wave impressing its own form on the sand below, which would be an impossibility, but because the moving current of water, as the tide advances or recedes, produces on the surface of the sand below the same form as the moving current of air produces on the surface of the water above. A rippled surface therefore to a rock is no proof of its having been necessarily formed in shallow water, though rippled surfaces are perhaps more frequently formed there, but simply a proof of a current in the water sufficient to move the sand at its bottom gently along, at whatever depth that bottom may be from the surface of the water.

Sandstones of all ages, from the oldest known rocks to the most modern, have occasionally rippled surfaces. Magnificent examples are sometimes shown in the cliffs of the S.W. of Ireland, where highly inclined beds exhibit such markings over spaces frequently of 160 feet in each direction. The size of the ripple, or the distance from crest to crest of the ridges, varies from half an inch to 8 or 10 inches, with a proportionate variation in depth between them.

Mr Sorby has lately shown that inferences may be drawn from the examination of these "current-marks" as to the strength and direction of the currents that caused them, and that we may thus reason back to some conclusions as to the physical geography of particular districts in former geological periods. One important conclusion certainly may be derived from these, as from other structures in rocks, namely, that the strength, velocity, and mode of action of moving water in the old geological periods was precisely of the same kind and intensity as those with which we are familiar at the present day.

In places where the current was troubled and confused, a modification of these rippled surfaces is sometimes produced, the bed being irregularly maculated on its surface, which is pretty equally, although irregularly, divided into smaller hollows and protuberances of a few inches diameter. This surface structure may be seen in process of production now, on shores where spaces of sand are inclosed by rocks, so that as the tide falls it is made to run in different directions among the rock channels; but it would probably be caused at any depth at which a current could be similarly troubled and confused. It is not unfrequently seen among gritstones, even those of the very oldest rocks. It might be called "dimpled current mark."

V.—CONTEMPORANEOUS EROSION AND FILLING UP.

Instances are not unfrequent in which it appears that a bed, not only of sand, but of clay, coal, or other soft rock, after being formed, has had channels or hollows cut into it by currents of water, and these hollows have been filled up by a part of the bed next deposited.

In fig. 8, taken from a road-cutting in the new red sandstone at Shipley Common, near Wolverhampton, 1 is a bed of red and white marl or clay; 2 is a chocolate-brown sandstone with irregular beds and patches of marl; 3 is a bed of red marl like 1, but which seems at one time to have been thicker than it now is, and to have had some part of its upper surface eroded off before the deposition of 4, which is a brown sandstone, that in like manner seems to have had its upper surface eroded and the hollows filled up by the deposition of 5, which is a mottled red-brown and white calcareous sandstone, or cornstone.

In the tertiary beds near Paris, which are believed to have been deposited in a shallow bay or gulf, receiving rivers, and therefore traversed by currents, this structure is frequent. Two remarkable examples are observable in the large excavation near the terminus of the Rouen railway. In a cliff about 40 feet high, in the fresh-water limestone formation, called the Calcaire St Ouen, two trough-like hollows may be seen about 50 yards apart; the beds previously formed having been excavated for a depth of 20 feet and a width of 15, and the hollows thus formed being filled up by irregular meniscus-shaped expansions of the upper beds. (See fig. 9.)

We are not aware how far the French geologists make a distinction in time between the beds thus eroded and those which fill up the hollows.

Similar trough-like hollows are met with in coal mining, traversing beds of coal, the coal being eaten away, and the hollows filled up by the matter which composes its roof, such as clay, shale, or sandstone. Mr Buddle has described very fully one met with in the forest of Dean, where the miners gave the name of "the horse" to the stuff which thus seemed to come down and press out the coal. This trough was found to branch when traced—as in coal-mining it was necessarily traced—over a considerable area, and to assume all the appearance of a little stream with small tributaries falling into it; the channels of the stream being afterwards filled up by the subsequently deposited materials that were spread over the whole coal.

Another modification of this erosive action is represented in fig. 10, taken from a sketch made in a quarry in the neighbourhood of Hobart Town, Tasmania, where a bed of soft brown unctuous clay, about a foot thick, b, lying between two beds of hard white sandstone, a and d, suddenly ended, and its place was occupied by sandstone, c, similar in character to the beds above and below it. We must in this case suppose that after the formation of the bed of sandstone aa, a bed of clay b was deposited over a certain portion of the area, and that then a current of water, bringing in sand, wore back the little bed of clay, eating into it so as to form a small cliff or step, and depositing the sand e afterwards against it, as represented in the diagram. The two beds, thus exactly on the same level, but not exactly contemporaneous, were finally covered by the bed of sandstone dd, which spread equally over both of them.

We see in this case proof, that although the bed c is exactly on the same level as the bed b, both reposing on, and both covered by, the same beds, yet they are still not exactly of the same age, but that c was formed subsequently to b, inasmuch as b was not only formed, but partially destroyed previously to the formation of c. Such facts give us farther proof of the length of the intervals which may elapse between the formation of two beds such as a and d, and also caution us not in all cases to infer strict synchronism from the fact of beds occupying the same geological horizon.

VI.—CONTEMPORANEITY OF BEDS ON SAME HORIZON.

If a group of beds, whether large or small, have the arrangement shown in fig. 11, the order of the formation of the beds is clear enough as regards a, b, and c; but d¹ and d² may either have been deposited contemporaneously, or one before the other; e is clearly subsequent to them both; but f¹ and f², again, are uncertain in relative age, while there is no doubt about that of g and h. If we wished to estimate the whole time consumed in the formation of such a set of beds, it would be obviously wrong merely to take their mean thickness, as shown at A B, for the measure of that time. The whole thickness of a had been deposited before b had been begun, and both were complete before e was formed. If, therefore, we assume thickness, or quantity of material deposited, as the measure of time occupied in deposition, it is clear that we should add together the maxima of a, b, c, and not take their mean. Similarly of the whole set, we ought to search out for the maximum GEOLOGY.

thickness of each bed, and add those thicknesses together; and in doing this, we should feel some doubt as to whether we ought not to reckon $d^1$ and $d^2$, and similarly $f^1$ and $f^2$, as two separate and consecutive beds, instead of supposing them to have been formed at the same time. If in the set of beds under examination we found many beds thus ending without overlapping, we should clearly be right in making allowance for the probably successive deposition of some of those which appeared to be contemporaneous.

We have already seen that this irregularity of deposition is most frequently met with in rocks that we supposed to be most hastily accumulated, while those which spread very regularly over extensive areas appeared to be most tranquilly and quietly, and therefore most slowly, deposited. We see now, however, that this very irregularity carries with it, in the long run, its own compensation, and that,—what with partial erosion and removal of some beds, and intervals of greater or less length between the formation of others, together with want of synchronism between beds that seem at first sight to possess it,—although any one bed, or small set of beds, may have been deposited in a comparatively hasty manner, yet the whole amount of time to be allowed for the accumulation of a great series of coarse beds would, if properly estimated, probably not be less than for an equal mass of more gradually and tranquilly formed rocks.

VII.—INTERSTRATIFICATION, ASSOCIATION, AND ALTERATION OF BEDS.

In studying the formation of aqueous rocks, we should soon perceive that no general rule can be laid down as to their association with one another.

Limestones, sandstones, and clays occur either separately or interstratified one with the other in every imaginable variety of disposition.

We have sometimes a series of beds, many hundreds of feet in aggregate thickness, of pure limestone, with scarcely a single seam of mechanically-deposited matter, even so much as an inch thick. Instances of this are shown in the chalk of the south-east of England, and the carboniferous limestone of Derbyshire, and of large portions of Ireland.

Series of beds of sandstone, almost entirely devoid of calcareous or argillaceous matter, and having a total thickness of many hundred feet, likewise frequently occur. Old gravel beds, now compacted into conglomerate, are often associated with these; and the sandstones exhibit every variety of texture, from lines of small pebbles to the finest possible grains. In such masses of sandstone it is rare to find any foreign bodies, and mineral concretions or chemical deposits hardly ever occur in them.

Groups of beds of almost pure clay also occur, with a thickness of several hundred feet, with hardly a single bed of sandstone or limestone to be found in them.

While cases of this accumulation of one particular kind of matter, of great thickness, and therefore through long periods of time, are by no means rare, it is perhaps more usual to find different beds of rock alternating one with the other, sometimes so interstratified that there is never a greater accumulation than twenty or thirty feet of any one sort without others interposed between them.

Beds of limestone are frequently separated by beds of clay or shale, which is most commonly black or brown. These shales are themselves sometimes calcareous, and there seems occasionally to have been such an equal mingling of the two kinds of matter, that it is hard to say whether it would be most proper to call the rock a shale or a limestone. Such are some of the beds known as calp shale or calp limestone in the middle districts of Ireland.

Beds of sandstone, again, often alternate with such shales; so that we get a series of beds consisting of alternations of all these kinds. Beds of limestone sometimes alternate with sandstones, some of which may likewise be calcareous; but it is more rare to find pure limestone and pure sandstone interstratified with each other, than to have argillaceous beds alternating with either or with both. Speaking generally, indeed, we find, in examining the vertical succession of beds of rock, an approach to the same kind of passage or gradation that we sometimes perceive in their lateral extension. Beds of very fine and very coarse materials rarely rest directly one upon the other. Conglomerates are generally covered and underlaid by sandstones, and not by clays or shales. Coarse sandstone, in the same way, has usually a bed of finer material, either above or below, before shale or clay occurs.

The transition from the conditions favourable to the deposition of one kind of rock to those conducive to another has generally been gradual rather than abrupt. The tranquil water of the open sea, which seems to be the general producer of limestone, becomes first invaded by gentle currents, bringing in finely suspended mud, before it is traversed by those of sufficient strength to carry out the coarser material of sand. When a single bed varies in grain, we generally find the coarser part at the bottom, as we should expect; for when a quantity of variously sized detritus is delivered into any water, the larger and rounder grains or fragments will be the first to sink. Not unfrequently, however, alternations of finer and coarser grained laminae occur in one bed, proving that the bed was formed by a succession of actions, and by as many different deliveries of matter into the water as there are sets of alternations.

We will give here two instances of alternation of beds, taken from actual observation and measurement. The first is a section supplied by Mr G. V. Dunmoyer, and represents the top beds of the upper limestone (carboniferous), where they are observed to pass into the lower coal measures, in county Carlow, from a quarry close to Old Loughlin. (Fig. 12.)

In this section the rule as to numbering is not observed, as the numbers refer to the woodcut. The following is another example of the alternation of beds, derived from the Bristol coal-fields (Mem. Geol. Surrey, vol. I., p. 210).¹

| No. | Feet. Inches. | |-----|---------------| | 23. | Argillaceous shale | 185 | | 22. | Sandstone | 4 | | 21. | Coal | 1 | | 20. | Underclay | 2 | | 19. | Argillaceous shale | 64 | | 18. | Coal and shale | 4 | | 17. | Coal | 1 | | 16. | Underclay | 4 | | 15. | Argillaceous shale | 4 | | 14. | Sandstone | 2 | | 13. | Argillaceous shale | 23 | | 12. | Coal | 9 | | 11. | Underclay | 3 | | 10. | Coal | 6 | | 9. | Underclay | 2 | | 8. | Argillaceous shale | 7 | | 7. | Sandstone | 1 | | 6. | Argillaceous shale | 2 | | 5. | Sandstone | 6 | | 4. | Argillaceous shale | 4 | | 3. | Coal | 2 | | 2. | Underclay | 2 | | 1. | Sandstone | 3 |

The whole section, of which this is a portion, enumerates 294 similar alternations, having a total thickness of 5084 feet, below which is a series of beds, 1200 feet thick, principally composed of hard sandstone.

It is to be specially noted, as regards the occurrence of coal, that it almost invariably rests on a fine argillaceous bed, often what is called "fireclay." This fact is familiar even to the miners, so that it has received the name of "underclay" in the South Welsh district, and in others is called "coal seat." The general order of superposition (or of time of formation, for these are convertible terms), is:

1. Sandstone; 2. Clay; 3. Coal; 4. Clay. If we disregard the minor alternations, we should see this rule carried out in almost all sections of coal measures, the clay above the coal (the roof) being generally thinner and stronger (more shaly) than that immediately below. In some few instances the coal seat is arenaceous, and still more frequently a sandstone or "rock" roof may be found.

VIII.—LATERAL VARIATION OF BEDS.

We should in many cases find that, of the beds which we had noted at one locality, many, or most, or all gradually thinned out and died away as we followed their lateral extension, and that their places were supplied by others which as gradually came in. Now, these new beds might either be of similar character to those which had died away, or altogether different.

We might, for instance, in one locality, have a series of limestones of 1000 feet in thickness, resting one upon the other, without the intervention of any other beds. As we traced this group across a country, we should perhaps find that little "partings" of shale began to make their appearance between some of the beds of limestone, and that as we proceeded these shales became thicker and more numerous, while the limestones became thinner in proportion. Some of the limestones would perhaps then altogether disappear, and the series be split up into two or more groups of limestone, with one or two intermediate sets of shale-beds.

Still farther on, the limestones might be more and more subdivided by beds of shale, and the shales themselves split up by beds of sandstone, until at length we should find our series consist almost entirely of sandstones and shales, with only one or two very subordinate beds of limestone, at one or two levels, to represent the purely calcareous group with which we commenced. The diagram (fig. 13) gives a rough representation of this lateral change, but requires to be drawn out to twenty or thirty times its length before it could be taken as a proximate delineation of the facts as they occur in nature.

In the same way, groups that consist principally of sandstone and conglomerate in one district, may in another be composed chiefly of limestone and shale or clay, with or without any beds of sandstone.

The scale upon which these lateral changes of character are carried out is altogether indefinite. We see it sometimes take place with respect to a small group of beds within the limits of a single quarry; in other cases, a distance of a few hundred yards or a few miles is requisite before the alteration is apparent. Some groups of beds, indeed, preserve their mineral characters but little altered over whole countries or across whole continents. Still, judging from what we know, we must always hold ourselves prepared for change even in the rocks that seem most constant in their characters; and as a matter of fact, we know of no one group of aqueous rocks that preserve the same mineral characters in all parts of the earth.

Combining thus actual observation with probable speculations, we should be quite ready to understand that the same set of beds may, within the space even of the British Islands, put on very variable characters. Of this we may now advantageously examine some instances. Let us compare the two following sections, which are descriptive of the beds which intervene between the two great continuous groups of argillaceous rock, called respectively the Oxford clay, and the Lias. These intervening beds are called generally the Lower or Bath oolite, because the oolitic limestones contained in them near Bath and elsewhere are the most striking and valuable portions of them. The section near Bath is taken from Conybeare and Phillips, that for Yorkshire from Professor Phillips's Geology of Yorkshire:—

¹ In all tabular lists of beds or formations in this article, the series will be arranged on the page in their order of superposition, but they will be numbered in order of age, beginning with the oldest or first formed. We see that, while in the south of England these beds are largely characterized by the presence of oolitic limestones, those in the north are almost destitute of them, but contain instead great beds of sandstone and shale, together with thin beds of coal, which are equally wanting in the south. If we examined the fossils they contained, we should find an equal change, as the beds in the north are full of carbonized plants and vegetables, which are almost altogether absent in the south, where the fossils consist of the remains of mollusca and other marine animals that are rare or wanting in the north. It seems as if in proceeding from the south to the north, we were approaching the shore of the old sea, and therefore get a greater quantity of mechanically-formed rocks, together with the products of the land, in the shape of plants that had been drifted from it, while the marine products proportionally decreased.

Had the Yorkshire rocks been those which were first examined and described, the term "oolitic" would never have been applied to them, although they may now be called "oolitic," as having been formed at the same time with those which had previously received the name of "oolitic" rocks in Gloucestershire, and other parts of the world.

Similar results would be arrived at if we traced over a large area another group of rocks, which are called carboniferous, from their containing in some places beds of coal. These rest upon certain beds of red sandstone, called old red sandstone; and if we compare them as they occur in the south of England and South Wales, in central and northern England, and in Scotland, we shall find that, while essentially made up of the same kind of materials throughout, these materials are differently arranged in different places.

We have in South Wales and the border counties—

4. Coal measures, alternations of sandstones, clays, and shales, with occasional beds of coal. 7,000 to 12,000 feet. 3. Millstone grit, chiefly white quartzose sandstone. 200 ... 900 feet. 2. Limestones with thin shaly partings, called carboniferous, or mountain limestone. 400 ... 1,800 feet. 1. Lower limestone shale, alternations of shales, with thin limestones. 150 ... 500 feet. Old red sandstone.

(Memoirs of Geological Survey, vol. I.)

In Derbyshire and some adjacent counties, and in North Wales, this series becomes:

4. Coal measures, as before. 3000 to 6000 feet. 3. Millstone grit, as before, about 800 feet. 2. Upper limestone shale, dark shale with occasional beds of limestone. 500 feet. 1. Carboniferous limestone, as before. 800 ... 1000 feet. Old red sandstone.

The chief difference between these two sections is the occurrence of a group of beds of black shale above the carboniferous limestone in the north, while there is little or none underneath it, the reverse being the case in the south.

In tracing these beds, however, from Derbyshire through Yorkshire and Durham to Northumberland, we find a gradual change coming in, so that while No. 4, the coal measures, retain their character of a multiform alternation of beds, No. 3, the millstone grit, becomes split up by shales with beds of coal, thus blending with the coal measures, while No. 2 acquires many beds of limestone and some of sandstone, and eventually also of coal, and even No. 1, the great limestone series itself, becomes interstratified with shales, sandstones, and coals; so that instead of the unbroken succession of beds of limestone which we have in Derbyshire, we get such sections as the following in Durham and Northumberland for the composition of No. 1.

g. Main limestone. 70 feet. f. Various alternations of shales, &c. 80 feet. e. Underest limestone. 24 feet. d. Various, including one coal-seam, one or more limestones, several shales, one or two principal grit rocks, flagstones, &c. 150 to 350 feet. c. Scar limestone. 15 ... 40 feet. b. Various alternations, including a bed of coal, and one or more beds of limestone. 125 ... 225 feet. a. Tyne bottom limestone. 25 ... 50 feet.

(Aldean Moor, as given by Mr Forster.)

In Scotland we have nothing above the old red sandstone but one great series of alternations throughout, containing beds of coal from the top of the series to the bottom, so that the great carboniferous formation is no longer separable into distinct groups as in the south. All that can be said of the Scotch carboniferous series is, that it is all coal measures, beds of limestone being more frequent in the lower than in the upper part of the formation, where they are commonly altogether wanting.

General Conclusions.—As general conclusions from what we have hitherto said, we may state the following:— 1st. For the production of mechanically-formed aqueous rocks the existence of dry land is absolutely necessary, since such rocks are the result, almost entirely, of the wear and tear of other previously existing rocks at or above the level of the sea. 2d. For the production of calcareous rocks animal life was necessary; for that of carbonaceous rocks vegetable life was necessary. The animal life may have been entirely aquatic, the vegetable life may have been either aquatic or terrestrial.

IX.—JOINTS.

We should not long have studied the laminated and stratified structure of rocks, and paid attention to their separation into beds by planes of division which were obviously the result of distinctness and succession in the acts of deposition, without being struck by the occurrence of other planes of division, which cut the first at various angles, and assist them in dividing the rocks into regular or irregular blocks.

We should, indeed, very soon perceive that all rocks, stratified or unstratified, igneous, aqueous, and metamor- were traversed by numerous planes of division of this kind. They may be seen in any quarry, or in any natural or artificial excavation in any solid rock, traversing the rock in various directions, and separating it into blocks of correspondingly various shapes and sizes.

These divisional planes are called "joints."

Without natural joints the quarrying of stratified rocks would be very difficult, and that of unstratified rocks almost impossible. If beds of sandstone or limestone were undivided by natural joints, each block would have to be cut or split by artificial means on every side from the rest of the bed; but in rocks, such as granite or greenstone, which have no beds, the blocks would not only have to be cut away on each side, but underneath also. It would obviously be a most impracticable task to dig out a large block of granite from the midst of a solid mass untraversed by any natural planes of division of any kind.

For the production of natural blocks of rock there must clearly be at least two sets of joints in stratified, and three sets in unstratified rocks, each set more or less nearly at right angles to each other. (See figs. 14 and 15.)

Professor Phillips tried many years ago, in his Geology of Yorkshire, whether the directions of the principal joints were not related in some way to the magnetic meridian, and arrived at results showing a tendency in the two principal sets of the joints of the Yorkshire rocks to arrange themselves according to certain magnetic bearings. This, however, seems to be only another way of stating that there are two principal sets of joints in the district, those of each set being parallel to each other.

Professor Sedgwick refers the directions of joints chiefly to the lines of upheaval and disturbance in rocks, calling those which run along or parallel to the "strike" of the beds, "strike joints," and those parallel to the "dip," "dip joints." All other joints he calls "diagonal" joints.

These are useful terms, whether the two things be or be not related in the way of cause and effect.

It is certain that some joints have been produced in all rocks anteriorly to, and independently of, the action of the forces of upheaval which have elevated them; but it is very likely that the direction of the lines of upheaval may have been governed or modified by that of the principal joints, and that other joints may have been the result of the action of these disturbing forces.

In some localities, very widely extended planes of division may be seen traversing a great series of beds in perfectly parallel lines, running at wide intervals down whole mountain sides, so as to be visible at a distance of several miles, but without producing any dislocation or shifting of the beds. Such unlimited joints were very probably produced, not from any internal shrinking on the mere consolidation of the beds, but from a simultaneous yielding of the whole mass to a great expansive or stretching force.

When we come, however, to examine the joints of igneous rocks, more especially those of the highly crystalline kinds, such as granite, we see an amount of irregularity and want of symmetry in their arrangement which would make it difficult to attribute their origin to any widely spread polar force or any mechanical power acting in one or two given directions. It is true that over small areas, as, for instance, in single quarries, the regularity of the arrangement of the joints in granite is often very remarkable. One set of planes will be seen to run at such equal distances, and so strictly parallel, that if they be horizontal, or nearly so, they produce the appearance of stratification in the rock, and the workmen frequently speak of the beds of rock between such planes (fig. 14). In very large quarries, however, or in long cliffs, this appearance of regularity is found to be very inconsistent and deceptive. One set of joints will most resemble stratification at one spot, and another set at another, each set being gradually obscured by the occurrence of other sets of joints cutting them irregularly and promiscuously.

The shape and the width of joints of stratified rocks vary much according to the nature of the rock. They are generally close, regular, and symmetrical, in proportion to the fineness of the grain and the compactness of the rock, being most irregular and uneven in coarse sandstones and conglomerates. The power of the force which produces them is, however, well shown in hard and well consolidated conglomerates, since the hardest pebbles of pure white quartz are often cut as clean through by the joints as the compacted sand in which they lie. In sandstones, joints are frequently open; in shales, they are closer, but more smooth and regular, being frequently perfect planes. In limestones, there are both close and open joints; but the open joints have frequently been widened by the action of water percolating through them, and dissolving a portion of the rock. Great fissures are sometimes formed in this way; and this has doubtless been the origin of many of the caverns which occur so abundantly in limestone rocks. In highly argillaceous limestones, the joints are often beautifully smooth, regular, and close.

In some cases, it would seem as if each bed had its system of joints formed before the other was deposited upon it, inasmuch as the joints formed in one do not penetrate the other. In other cases, a set of joints is seen to be common to a whole set of beds, and to have been produced ap-

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1 For the explanation of the words "strike" and "dip," see pages, chap. vi., § 2. for joints, in passing from one bed to another, to shift a little, or slightly change their angle. In such cases it may be doubtful whether a joint previously formed in the one bed may not have given rise to the formation, or at least have modified the position, of the other, in the bed above. There does not seem either to be any reason why all the joints traversing any bed or any set of beds should necessarily be of one age, but the contrary, insomuch as we may imagine the process of solidification to take place at intervals, being at first incomplete, and afterwards becoming more perfect. Subsequent contraction would not have been so likely perhaps to widen the old joints as to produce new ones, since the shrinkage could hardly exert such a force as to overcome the effects of friction, and cause any large masses of rock to move and slide one over the other even to the most trifling extent.

Joints then may be caused, first, by the consolidation of each bed separately; secondly, by subsequent acts of consolidation, common to several beds; and thirdly, to widely spread mechanical force, affecting whole formations at once.

In the gypsum quarries of Chaumont, near Montmartre, Paris, two thick beds of granular gypsum occur, which, instead of being divided by two principal sets of joints into quadrangular blocks, are traversed by three equally strong sets crossing each other at equal angles; and the whole mass is accordingly split into triangular and hexagonal blocks, giving the beds a columnar appearance like that so well known in basaltic rocks. (See fig. 16.)

The hexagons and triangles are frequently quite regular and perfect, and the result very curious, and, as far as I am aware, unique in unaltered aqueous rocks. If three sets of equidistant planes cross each other at equal angles, the angle of intersection between any two will of course be $60^\circ$. If all three planes meet at the same points, triangular forms only would be produced; but if they be so arranged as that no more than two sets should ever intersect each other at the same point, and that each point of intersection be exactly half way between the other set of planes, as in fig. 16, alternate triangles and hexagons of perfectly regular form will be the result.

These conditions seem to have been exactly fulfilled in the quarries near Paris, and the symmetry of arrangement has not been disturbed or obscured by additional irregular joints, which may possibly mask this, or some other symmetrical arrangement of joints in other places.

We have already said that in massive igneous rocks there must necessarily be at least three sets of planes, all more or less nearly at right angles to each other, for the mass to be separated into blocks, while in stratified rocks there must be at least two sets of joints cutting across the beds. If the planes be equidistant and exactly at right angles, the blocks would be perfect cubes. This exact regularity however, is not to be expected as common, nevertheless the approach to it is frequent, and it would be still more so if it were not for the occurrence of other irregularly disposed diagonal joints. We may, therefore, in practice look upon such blocks as more or less universally cuboidal, and speak of the joints producing them as cuboidal or quadrangular joints. We have just seen that, even in aqueous rocks, other symmetrical arrangements of joints may exist, producing regular forms other than cubes; but this is more especially remarkable in those igneous rocks which occur in comparatively thin sheets, whether as beds or as "dykes," that is, as wall-like sheets traversing other rocks. In these the joints often divide the mass into long prisms.

The sides of these prisms are sometimes regular and equal, producing either hexagonal, pentagonal, or other forms. Sometimes, however, they are unequal and irregular, dividing the rock into uneven and wrinkled prisms like those exhibited by the common substance "starch."

That this prismatic arrangement is the result of contraction on consolidation is shown by the prisms usually being at right angles to the greatest extension of the mass, being vertical in a horizontal bed, horizontal in a vertical dyke, proving that the fissuring commenced at the cooling surfaces, and struck thence directly towards the centre of the mass.

Sometimes it is found that the two sets of prisms thus originating at each surface did not exactly fit when they met in the centre, as is shown in fig. 17. At other times, however, they proceed uninterruptedly from one side to the other, the two sets either having coalesced, or one surface having cooled before the other, and given rise to divisions that were carried right across to the other.

In addition to these prismatic joints, other irregular joints, more or less nearly at right angles to the prisms, also occur; and in very regularly columnar basalt and greenstone the columns are articulated, or separated at regular or irregular intervals into short blocks, by divisions, which are sometimes quite flat, sometimes curved into concave and convex surfaces, forming a kind of approach to a ball and socket joint. The origin of this structure is explained by the celebrated observations of the great Gregory Watt. If a mass of basalt be melted in a furnace, and allowed to cool again, the following results may be observed. If a small part be removed and allowed to cool quickly, a kind of slug-like glass is obtained, not differing in appearance from If it cool in larger mass more slowly, it returns to its original stony state. During this process small globules make their appearance, which, very small at first, increase by the successive formation of external concentric coats, like those of an onion, and the simultaneous obliteration of the previously formed internal coats, so that ultimately a number of solid balls are formed, each enveloped in several concentric coats. As these balls increase in size, their external coats at length touch, and then mutually compress each other. Now, in a layer of equal-sized balls, each ball is touched by exactly six others (see fig. 18), and if these be then squeezed together by an equal force acting in every direction, every ball will be squeezed into a regular hexagon. But the same result will follow from an equal expansive force acting from the centre of each ball, or from the tendency to indefinite enlargement in their concentric coats. Each spheroidal mass, therefore, will be converted into a short hexagonal pillar. But if there are many piles of balls one above another, each ball resting directly and centrically on the one below it, we should have a long column of these hexagonal joints, and the top and bottom of each joint either flat, concave, or convex, according to variations in the amount and direction of the pressure at the ends of the columns.

There is no apparent reason why, in a cooling mass of basalt, the balls should be so arranged as that their centres should be in straight lines, and that the hexagonal vertebrae should form straight continuous pillars rather than separate discontinuous pavements. This, however, is probably the result of the simultaneous tendency in the mass to split into prisms in consequence of the joint-forming contraction on consolidation, the two tendencies acting together to produce the columns with the short ball and socket articulations.

In the case of curved columns, it is probable that the accidental arrangement of the centres of the balls overpowered the tendency to produce straight prismatic joints. Many other irregularities, resulting from the unequal action of one or the other tendency, may frequently be observed, since there are not only curved, but oblique and radiating columns; not only hexagonal, but pentagonal, triangular, and other irregular shapes; and in some instances, small uncompressed, or nearly uncompressed balls, may be found in the interstices between unequal and irregular columns. The pillars of basalt are usually from 6 to 18 inches in diameter, and vary in length from 5 or 6 to 100 or 150 feet. Columnar greenstone is commonly on a larger scale, the pillars being sometimes 5 or 6 or even 8 feet in diameter, and the columnar form of the rock is often only to be perceived at a distance. Almost all greenstone exhibits the tendency to decompose into rounded spheroidal blocks, on which we have just seen the columnar structure partly to depend. Felstone is sometimes also beautifully columnar; of which an admirable example may be seen in a small pass to the southward of Lough Gitanie, near Killarney. (See papers by Messrs Dunoyer and Foot in the Journal of the Geological Society of Dublin, in 1856.) Neither is this tendency confined to basalt, greenstone, and felstone, since it is sometimes perceptible even in granite, producing in that rock the logging stones," or "rocking stones," the "cheese wrings," the "tors," as well as the "pots and pans," and "sacrificial basins," and other curious natural forms occurring in that rock, of which many have been attributed to ancient artificial processes.

The study of joints and the other divisional planes of rocks, and the different forms assumed by them in consequence, both when freshly exposed and when modified by "weathering," is as necessary for the landscape painter who wishes to reproduce nature, as is the study of anatomy to the figure painter. Mr Ruskin has handled this subject in his usual masterly style.

**CHAP. VI.—FORCES OF DISTURBANCE.**

**I.—ELEVATION OF AQUEOUS ROCKS.**

In the preceding chapter we have been principally engaged with the facts relating to the deposition and consolidation of those rocks that have been formed under water. It will be convenient now to examine the problem of the elevation of those rocks into dry land.

It is clear that all rocks which were formed at the bottom of the sea, and which are now dry land, must have gained their present situation either by the sinking of the sea level or by the uplifting of the sea bottom. If, however, the level of the sea be materially lowered in any one part of the globe, it must be equally lowered over its whole surface. But we find aqueous rocks on the summits of some of our highest mountains, and if these had been laid dry solely by the sinking of the sea, it is difficult to understand what can have become of a shell of water ten or twenty thousand feet deep enveloping the whole globe.

Partial floods and inundations are out of the question. Laplace determined that though the sea is often agitated by storms and earthquakes which raise it into great waves, and make it locally and temporarily overstep its limits, yet the equilibrium of the ocean is stable if its density is less than the mean density of the earth. Now, experiments on the attraction of the mountains of Schehallion in Scotland, and Mount Cenis in the Alps, as well as those made by Mr Cavendish, and Reich and Bally, with balls of lead, demonstrate that the earth has a mean density at least five times that of water, and hence the stability of the sea and the invariability of its level is beyond a doubt.¹ (Brewster's Life of Newton, vol. i., p. 363.)

We must therefore look upon the level of the sea all over the surface of the globe as absolutely invariable, unless by very great changes taking place in the form of its bed,—the elevation of some parts, or the depression of others. To effect either relative or absolute change of level, then, in the surface of the sea, it is the solid part of the earth's crust that must first move. Even then we shall not effect absolute change of level in the upper surface of the sea, unless the elevation of its bed in one place be materially greater than its depression in another, or vice versa. But this we have no reason to suppose probable, and no right to assume as having taken place.

Wherever, then, we find that a change has occurred in the relative levels of land and sea in any portion of the globe, we must believe that the elevation or depression has taken place in the land,—in the solid rock, and not in the

¹ More recent observations by the Astronomer Royal on the pendulum at the surface and at the bottom of deep mines, give a mean of 6.809 for the earth's specific gravity, while those made by the Ordnance Survey on the deflection of the plumb line at Edinburgh give it as 5.14. The very fluidity, indeed, of the ocean, which might at first lead us to look to its motion and change of place as the cause of the appearance of dry land, renders any permanent local or partial change in its level impossible, while a local change in the level of solid rock is more easily possible than a general or universal one.

If, therefore, we can prove that elevation has occurred in one place while depression happened in another, or if we can prove that any alteration of level whatever took place that was not common to the whole globe and equal all over it, it must necessarily have been the rock that moved, and not the sea.

We may arrive at this conclusion in another way. We could not continue our observations upon stratified or aqueous rocks very long without perceiving that their beds were not invariably horizontal, but were, on the contrary, generally inclined to the horizon. Now we have already seen that in certain cases beds of stratified rock may be formed on a considerable slope, or may have an original inclination due to the very circumstances of their deposition. These cases, however, are by their very nature limited to small areas. A steep slope cannot be of indefinite extent in every direction, and could not have strictly parallel beds deposited on it over its whole area if it were. Whenever, then, we have very widely spread beds maintaining an equal thickness and strict or approximate parallelism over a large extent of ground, we may feel perfectly sure that those beds when first formed were horizontal. If such beds are now found in an inclined position, we may be equally certain that they have been moved since their formation, and moved more in one direction than in another. They must have been tilted, either by being lifted up at one end or depressed at the other. In many cases we find this motion to have been very great; the beds have been tilted and set on edge so as to rest at very great angles, and in some cases to be absolutely vertical. Beds consisting of alternations of clay and sand, with their seams of round pebbles that must clearly have been deposited horizontally, have been tilted up till they are now perpendicular (see fig. 19).

No one could look at a cliff exhibiting these facts without feeling certain that in this case, at all events, some submarine and internal forces had acted upon previously horizontal beds, and lifted them into their present position.

If we still hesitated to believe such motion in the solid frame-work of the earth possible, our scepticism must at length give way before the knowledge of the fact that it is still going on even in our own day in various parts of the earth. For a compendious account of movements of elevation and depression in the lands of the present day, either occurring within the times of history or still in progress, we must refer the reader to Sir C. Lyell's Principles of Geology, chapters xxix., xxx., and xxxi. He will there find an account of the gradual rise of Sweden and Norway, which is now going on at the rate of about three feet in a century; of the frequent elevation of land along the west coast of South America simultaneously with the occurrence of earthquakes; of the depression of the coast of Greenland, and of both the elevation and depression of the temple of Jupiter Serapis and its neighbourhood in the Bay of Naples, and other similar facts in other parts of the globe.

It must suffice here to say, that these movements seem to be very slow, and to require immense periods of time before any great permanent change is effected. They may either be continuous and insensible in small periods of time, with no earthquake movement, or they may occur simultaneously with earthquakes in little shocks and starts of a few feet or a few inches at a time. It is probable that no earthquake ever occurs without being accompanied by some change of level in some part of the rock shaken by it.

For the cause of these movements we must look to fluctuations of temperature in the heated interior of the earth—great accessions of heat rising nearer the surface in one part than another, causing expansion of the rocks affected by it in every direction, and thus producing an outward bulging or elevation of these rocks, accompanied by injection of molten matter among them; depression, on the other hand, being due to local refrigeration, and consequent shrinkage and contraction. As to the cause of the fluctuations of temperature, we are perhaps not in a condition to give even a guess.

To such movements as these, operating thus slowly and gradually, we must ascribe the elevation of the whole of the present lands of our globe above the waters of the sea. We say the whole of our present lands, because by far the greater portion of the dry land is covered by or made of rock that has been deposited on the bottom of the sea; and of the remainder, where igneous rocks now prevail at the surface, we have every reason to believe the greater part at least, if not the whole, was once covered by aqueous rock. With the exception, then, of those spots which are composed of matter actually ejected from the mouth of a recent volcano, we either know or must believe that the whole of our present lands have been once beneath the sea, and have been gradually elevated above it.

To such gradually acting forces as those we have mentioned we must ascribe not merely the elevation of all land, but all those effects of unequal elevation, of tension, of disturbance, and of great pressure resulting in fracture and contortion, which I am about to describe. If we know that such is the character of the forces now in action, and if such forces be capable of producing the effects, provided only a sufficient amount of time be allowed them, we have no right to assume that these forces have ever had a different character or a different intensity, unless good reason

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1 Mr Mallett, in his Report on Earthquakes in the Proceedings of the British Association, points out that these movements are not caused by the earthquake, which is a mere undulation, but accompany it; and that it would probably be more correct to say, that the earthquake was caused by the movement.

2 More recent movements still were mentioned by Sir C. Lyell, in a lecture to the Royal Institution in 1856, as having occurred in New Zealand simultaneously with the earthquake of January 1855. A step of rock, bared of earth, nine feet high, was traceable for ninety miles at the edge of a plain along the foot of a range of hills. An elevation of five feet took place on the north side of Cook's Straits, so as almost to exclude the tide from the river Hutt, and a corresponding depression on the other side of the straits allowed the tide to flow up the river Wairau several miles higher than before.

That these permanent changes of level have not been more often observed is probably in great part owing to the want of a natural standard of level. A change of level diffused over a considerable area could only be detected on the sea-coast, or by accurate measurement referring to some standard of level which had not itself been disturbed. Our only natural standard of level is that of the upper surface of the sea. can be given why the amount of time could not have been large enough. If, however, it is proved from other sources that the time occupied by geological action is practically illimitable, we are not warranted in diminishing the amount of time and increasing the intensity of force simply to suit our preconceived ideas. This caution is necessary because errors in estimating the nature of the forces in operation not only lead to false theoretical reasoning, but occasionally even to practical mistakes based upon that reasoning.

II.—INCLINATION OF BEDS.

The inclination of beds downwards into the earth is technically called their "dip." It is measured by the angle between the plane of the beds and the plane of the horizon. In fig. 20 the beds dip to the south at an angle increasing from 35° to 50°. When we speak of the opposite of "dip," we use the term "rise." For instance, in fig. 20 the beds dip to the south and rise to the north. The place where each bed rises out to the surface of the ground is called its "outcrop" or "basset." We say that such and such beds "crop out" to the surface, and we speak of the "basset" edges of the beds. Miners use these and other terms, such as "coming out to the day," "rising up to the grass," when speaking of the "outcrop" of any bed or beds. The line at right angles to the dip, that is, the line of outcrop of a bed along a level surface, is called its "strike," a term introduced from the German by Professor Sedgwick. It is described by its line of compass bearing, either true or magnetic. It may be called the "range" of a bed or beds across a country. Coal miners commonly speak of this as the "level bearing" of a bed, seeing that if you draw a line or drive a gallery along a bed exactly at right angles to its line of dip or inclination, it must of necessity be on a true level, or have no inclination either way.

If, then, a bed "dips" due north or due south, its "strike" will be due east and west. If we know the direction of the "dip" of a bed accordingly, we also know

1 Geologists generally use true compass bearings, a practice that ought to be adopted universally in all land operations. GEOLOGY.

The exact bearing of its "strike;" but if we only know the strike, we do not necessarily learn either the direction or amount of its "dip," because it may incline to either side of the line of strike, and to any amount from the horizontal plane. In making observations, then, in field geology, it is most important to observe accurately the direction of the dip of all stratified rocks. It is also important to know its amount; but this need not be observed with such minute accuracy, since it is apt to vary continually to the amount of $3^\circ$ or $4^\circ$. In figs. 20 and 21 we have a rough map and section of a piece of country, which will explain these terms. In fig. 21, let A.A be a rocky beach exposed at low water; B.B a line of cliff about 100 feet in height; and C.C the surface of a country above the cliff, with the rock bared of grass and soil, and exposed in several places, either on the summits of eminences or the bottoms of quarries. The arrows point out the direction of the dip, the figures showing its amount. This amount increases from $35^\circ$ on the north to $50^\circ$ on the south; and we may assume this increase to be quite gradual, or that the beds are parts of curves and not of perfectly straight planes. Then let D.D be a line of section, or supposed cutting, at right angles to the strike of the beds, and let this section (fig. 20) be drawn so as to give the true outline of the ground across which it passes, and representing the beds in the true position they would be seen to occupy were such a cutting or cliff really formed. Being drawn at right angles to the strike, it runs of course along the line of the direction of the dip, and its bearing, as here drawn, is about $25^\circ$ west of north, and $28^\circ$ east of south. The latter, then, is the direction of the dips. The bearing of the strike marked by the ranges of the beds across the map will consequently be $28^\circ$ north of east if we look in one direction, $28^\circ$ south of west if we look in the other. In such a locality as this, if we marked out the boundaries of the beds correctly on our map, we should feel sure of the correctness not only of the map, but of the section, and we should know the position of the beds not only above the level of the sea, but for a considerable distance below it. If, for instance, at the point d in the map it was of importance to sink a shaft, so as to come down upon the bed b, we should see at once that the depth of b under d would be, according to the scale, rather more than 425 feet. If we wished to reach the bed a in the same way, it would be easy, either by construction or calculation, to ascertain the depth at which it would be found in a perpendicular shaft under d.

It would be easy for us also to ascertain the total actual thickness of the whole set of beds shown on the map, either by actual measurement of each bed along the shore, or by constructing a section founded on the observation of their angle of dip and the width of their outcrop. The actual thickness of the beds cut by the sea-level line in the section Fig. 20, for instance, would be a little over 850 feet. That is to say, those beds, if they were horizontal, would be 850 feet from top to bottom; if they were vertical, it would be 850 feet directly across them; while, in their present inclined position, a straight line across their outcrop measures 1200 feet.

If we proceeded to trace those beds into the country along their strike, however much the direction of the strike or the angle of the dip might vary, or however they might be concealed by grass, soil, or superficial covering, we should always have to recollect that there was a thickness of 850 feet of beds to be found or allowed for somewhere; and if in the course of a few miles we came to a quarry or a cutting where the bed x, for instance, was shown, and we were able certainly to identify it, we should expect there to find all the other beds above and below it that we had found above and below it where they were clearly exhibited. We should feel sure we were right in this, if in the expected spots, at the requisite distance on either side of it, we found one or more of the beds a, b, or c, shown in other quarries, or cuttings, or cliffs in the neighbourhood. It is in this way, by getting a knowledge of the true sections of a series or group of beds where they are well exhibited, and following them across a country, picking out one of them here, and another of them there, in ditches, brooks, river banks, cliffs, or ravines, wells, mines, road or railway cuttings, and quarries, that geological maps are constructed, showing the boundaries of the several groups of rock, their range or strike across a country, and the area of surface they occupy with their outcrops or "basset edges."

III.—CONTORTIONS.

Where the dip and strike of the rocks are very steady, or where they run in nearly straight lines across a country, and their edges are not too much concealed by superficial covering, this is a task of no great difficulty. In many instances, however, neither the dip nor the strike of a set of beds remain constant over any considerable spaces. The beds are bent and contorted, and twisted about, so that, instead of running in straight lines, the basset edges, or outcrops of any set of beds, follow crooked and curved lines, often doubling back and running altogether out of their former course. Moreover, after dipping down in a certain direction for some distance, such beds are frequently curved up again, and rise to the surface at some other locality, forming basin or trough-shaped hollows; or, again, after cropping out to the surface, the beds underneath them are bent over in a ridge-like form, so that the first beds come in and take the ground again, dipping in an opposite direction.

These bendings and twistings of the beds occur on every possible scale, from mere little local crumplings on the side of a bank, to curves of which the radii are miles, and the nuclei are mountain chains. When on the small scale, they are commonly called "contortions," as in fig. 22.

There are in some instances wonderfully regular curves visible in beds even of the hardest stone, such as beds of limestone, arches both upwards and downwards, succeeding each other with all the regularity of masonry, as in fig. 23.

In other cases, especially where there are alternations of

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1 In diagram fig. 21, the supposed quarries or exposures of rock in the interior of the country are thickly grouped together; but if the reader will imagine them separated by much wider intervals, and scattered over a far larger space, he will have a truer notion of what usually occurs in nature. softer and more yielding beds with hard ones, the softer are seen to be puckered and crumpled, as if they had been subjected to lateral pressure and squeezed back, while the harder ones are less broken. This is shown at one part of fig. 22.

Very curious and almost inexplicable contortions may be seen occasionally, but we must recollect, that the conditions under which they were produced, were such as it is not often possible for us to imitate, nor easy even to imagine. When the rocks were thus contorted, they were buried under vast thicknesses, often many thousands of feet, of other rock; the rocks above and below them were also of unequal densities, and offering unequal resistances to force; the forces of disturbance, therefore, even if uniform in their origin, would become complicated in direction, and unequal in intensity, by reason of these inequalities in the structure and position of the rocks, and inequalities in the pressure of the superincumbent masses. We might expect *a priori*, therefore, to meet sometimes with results not capable of any ready or simple explanation.

IV.—ANTICLINAL AND SYNCLINAL CURVES.

When the curves of the rocks are of greater extent, we cease to speak of them as mere "contortions." If the curves have longly-extended axes, that is to say, if the beds are bent up into ridges, or down into troughs, which continue for considerable lengths, in proportion to their widths, we speak of them as "anticlinal" and "synclinal" curves. If, on the contrary, no diameter of the curved area be much longer than another, we call them either dome-shaped elevations, or basin-shaped depressions, as the case may be.

In fig. 24, A is an anticlinal, and B is a synclinal curve, the beds numbered 6, 7, 8, being repeated on each side of both. At A, the lower beds 1, 2, 3, 4, 5 are seen rising out from underneath them in the form of an arch. At B, the upper beds 9 to 13 repose upon them in the form of a trough. It matters not whether we suppose the spaces 1, 2, 3, &c., to represent single beds, and the hill at A a slight elevation, or whether they be taken as groups of beds, and A be supposed to be a mountain chain. The straight line which may be supposed to run directly from the eye of the spectator along the top of the ridge A, or the bottom of the trough B, is called the "axis" of the curve in each case. This axis may be either horizontal or inclined; if horizontal, the section across it will cut the same beds wherever it be taken, the variations in its outline only resulting from those in the outline of the ground. If, however, the axis be inclined, different sections will cut different beds, even should the outline of the ground remain the same. This will be best shown if we look at fig. 24, which is a supposed plan of the ground of which fig. 25 is a section, and suppose the axis AA' and BB' to incline downwards to the north, or from the line of section to the other end of the map, as shown by the arrows, it is obvious that the bed 4, which forms the apex of the ridge in the section, will slope downwards along the inclined axis, and if the ridge of the hill be kept up to the same height, the beds 5, 6, 7, 8, will necessarily arch over it. In the same way, if the synclinal axis BB' slope in the same direction, there must either be a corresponding slope and hollow in the surface of the ground, or fresh beds, 14, 15, 16, &c., must come in, resting in the hollow of 13.

In countries traversed by many lines of disturbance, such forms as these are by no means unfrequent. They necessitate great labour in tracing them out, and making an accurate map of them, especially where the ground is itself lofty, broken, and uneven, and the complexity underneath obscured by perplexing irregularities on the surface.

Sometimes the axes of the curves slope both ways from a central point, producing long oval forms like that of an inverted boat, and there is a regular gradation from these to the circular elevations or depressions mentioned before, in which the beds are said to have a *quaquaversal* dip from or to a central point, according to whether it be a dome or a basin that is produced.

These flexures are in some instances carried out so far, both on the large and small scale, as to produce actual inversion (see fig. 26) of the beds, so that the lower surfaces appear to be the upper ones.

This inversion may be seen in some cases in cliffs among highly contorted beds; in other cases it requires a more widely extended observation in order to show that the apparent order of superposition of any set of beds, in any particular locality, is the inverse of that order which is to be observed generally, and where the beds are undisturbed.

Inversion of beds is occasionally to be detected by means of the "ripple," or "current mark," or other structure produced on the surface of beds, when the peculiarities in the forms of these marks are of such a kind as that a "cast" of them shall be plainly distinguishable from the original form. In these cases the "cast" may sometimes be seen on the now upper surface of a bed, dipping under what appears to be the bottom of the superincumbent bed, but which was originally the really upper surface or "mould" on which the materials were deposited that formed the "cast" at the bottom of the succeeding bed.

The inversion of beds is likewise occasionally detected in coal mining, as in Belgium and the south-west of Ireland, where beds of coal are sometimes found with the "coal-" It may easily be conceived, that the force which was sufficient to raise vast masses of solid rock, of unknown but immense thickness, from the bottom of the sea high into the air, in order to form the dry land, and to bend them into the folds and contortions we have just described, was also sufficient to crack and break them through. We find, accordingly, very frequent instances of cracks and fissures running through great thicknesses of rock. Sometimes these are mere fissures; but quite as frequently there is not only a severance but a displacement of the rocks that have been severed. Beds that were once continuous are now not only broken through, but are left at very different levels on opposite sides of the fissure, many feet, or many hundreds of feet above or below the parts with which they were once continuous. When this is the case, these fractures are called "faults" or "dislocations" by geologists, for which miners in different districts use in addition the terms "slip," "slide," "heave," "dyke," "thing," "throw," "trouble," "check," and other expressions.

The amount of dislocation, measured in a vertical direction, produced by a fault, is called its "throw;" a fault being said to be an "upthrow" or a "downthrow" or an "upcast" or "downcast," according to the side from which we view it. Its amount is stated in fathoms, yards, or feet, measured perpendicularly from the surface, provided the surface be horizontal, from a given horizontal plane if it be not. If, for instance, a bed of coal, where it is cut by a fault, as at A (fig. 27), be 100 yards from the surface, and traverse, whether they be hard or soft, or an alternation of both.

2dly, According to the position of the beds which they traverse, whether these be horizontal, inclined, or contorted.

3dly, According to the number of lines of fracture, their direction, inclination, and combination.

1. When faults traverse a mass of rather soft and yielding rocks, such as shales and thin sandstones, the fissures themselves are often mere planes of division, just as if the rock had been cut through with a knife. Very frequently, in this case, the two contiguous surfaces of the fault are found to be quite smooth and polished by the enormous friction that has taken place, producing the appearance well known to geologists under the name of "slickenside." In some cases, although the fracture seems quite clean and sharp, yet the beds on each side are found to be traversed by a great number of small, irregular, and discontinuous "slickenside" surfaces, as if a jarring and tremulous grinding motion had been produced in the mass of the beds. Sometimes the beds end abruptly without any distortion (fig. 28); but sometimes they seem to have bent and pulled down along the plane of the fault to a certain extent, as in fig. 29.

In fig. 29 the beds would be said to "rise towards the upthrow," and "dip towards the downthrow;" and this is naturally the most usual occurrence, though we believe not invariably, as there are said to be instances where the very opposite of this takes place, and the beds seem to "rise" to a downthrow fault.

When faults traverse very hard and unyielding rocks, such as thick hard gritstones, hard limestones, or hard siliceous slates, and still more, if they penetrate igneous rocks such as granites and felstones, the fissures are apt to be much wider, and often very irregular. If the original fracture shall have taken place not in one plane, but so as to produce two jagged, and broken, or uneven and irregular surfaces, with cavities and protuberances as in fig. 30, and these two surfaces slide one over the other, it is very unlikely that they would ever, unless restored to their original posi- Geology, be made to fit exactly, so as to close again upon each other throughout their extent. Protuberance might rest against protuberance, or come against a hollow not large enough, or not of the requisite form, to receive it, and thus the two walls of the fissure would be kept partially and irregularly apart, the fissure being closed in some places and open in others. In fig. 30, an uneven fracture having traversed the hard beds A, B, C, D, and dislocation taken place, the result would be the irregular fissure EF.

It is true that the grinding process, as the surfaces moved upon each, would often greatly diminish this irregularity, and in soft rocks probably obliterate it; but in hard rocks it is much more usual to find the irregular openings above described still remaining.

Where alternations of hard and soft beds occur, there may be a combination of the two effects, the fissure being quite closed where soft beds are brought together, or even where soft beds are brought against hard, but more or less open where two hard beds come in contact.

When we speak of open fissures, however, we by no means intend to assert the frequency of fissures now open and empty. They are almost invariably filled with materials either derived from the ruins of the adjacent rocks at the time of the fracture occurring, or accumulated there afterwards.

Some fissures, even in the most soft and yielding rocks, have similarly been kept open, or rather the sides of the fault kept apart by fragments and debris that were dragged into them at the time of their occurrence. Such fragments, often of large size, are found along the lines of faults both vertically and laterally, for it is not unfrequent, in tracing the line of a fault along the surface of the ground, to find lumps and patches, some yards in diameter, of the broken beds caught and resting in the gaps of the fracture.

2. As it is comparatively rare to find beds in a strictly horizontal position over any considerable area, it is necessary to study the effect of faults on inclined beds, and on beds with an inclination varying either in angle, in direction, or in both. If any bed or set of beds "striking" in a given direction, and "dipping" at a given angle, be broken through by a fault, the effect of the vertical "throw" is to produce at the surface the appearance of a lateral "shift."

Let us suppose fig. 31 to be a horizontal plan of the outcrop of a set of beds, of which we may suppose aa to be a limestone interstratified with sandstones and shales, and that they all dip steadily to the N., at an angle of 25°, and that these beds are traversed by the fault bb, causing a "downthrow" to the E., or an "upthrow" to the W., which is the same thing. It is evident, then, that the outcrop of the beds will be farther S. on the E. side of the fault than they are on the W.

To render this more evident, let fig. 32 be a diagrammatic section along the direction of the line of fault, showing the beds on both sides of it, and let us look only at the limestone aa, disregarding the other beds. If we suppose the part b dropped vertically down to c, and the part d in the former continuation of the bed down to e, it is clear that a vertical throw of the bed aa on one side of the fault will place it in the position a'a' on the other side of the fault, the respective outcrops of the two pieces of the same bed being, at the present surface of the ground, at the points bc. In other words, the apparently lateral shift of the outcrop of aa in the plan (fig. 31), has been produced by the vertical throw of the inclined beds on opposite sides of the fault. It follows, also, that the higher the angle at which the beds dip, the less will be the apparent shift at the surface produced by the same amount of throw. In fig. 33 the angle of inclination is increased to 60°, the vertical throw, or the distance between b and c, remains the same as in fig. 32; but it is obvious that the apparent lateral shift or distance between b and e is greatly diminished. This diminution would continue with the increase of the angle of inclination, until the beds were actually vertical, when it is plain that no amount of vertical throw could produce any apparent lateral shifting, for the ends of the beds on the opposite sides of the fault would merely slide up or down along each other. In a set of vertical beds, then, it would be almost impossible to detect a fault, however great may have been the real fissure and dislocation. On the contrary, when the beds lie at a very low angle, a very small dislocation shifts the outcrop of the beds in a very remarkable manner.

It is obvious, from an inspection of figs. 32 and 33, that if we know the inclination of the beds, and the amount of Geology. the vertical "throw" of the fault, we may easily calculate what will be the apparent shift of their outcrop at the surface; and if, therefore, we find the outcrop of one, it will be easy to discover the outcrop of the other.

On the other hand, if we know the distance between the outcrop of the beds on opposite sides of the fault and their angle of inclination, it will be easy to calculate the amount of the vertical "throw," or to discover the depth (or distance, be) at which the one part of the bed will be found lower than the corresponding point on the other side of the fault.

In practice, allowances have to be made for irregularity in the surface of the ground, and for variations in the angle of inclination of the beds, and also for changes in the amount of "throw" in the fault, but in the above consideration of the simplest case lie the elements of much practical utility in mining and other operations.

That this apparent lateral shift at the surface is really due to vertical elevation or depression, may be shown further by examining its effect on beds thrown into anticlinal and synclinal curves.

Let fig. 34 be a plan in which aaa is a bed having a synclinal or basin-shaped depression at SS, and an anticlinal form at AA, dipping, as shown by the arrows, at an angle of 60° in each direction, and let it be traversed by the fault FF. It is clear that no lateral shifting will account for the places of the broken ends of aa on opposite sides of the fault, since they are shifted in opposite directions; while their present positions are easily and obviously accounted for on the supposition of a vertical elevation on the side of the fault marked uu, or depression on that marked dd, and a subsequent planing down of the whole to one level surface. If we draw two sections parallel to the fault, and on opposite sides of it, one, as in fig. 35, along uu, the upcast side, and the other, as in fig. 36, along dd, the downcast side, putting in the beds with a dip of 60°, as directed by the arrows in the plan, we should at once see that, in fig. 35, on the upcast side of the fault, the beds will meet below S, at a point much nearer the surface than they do in fig. 36 on the downcast side; in other words, that the bottom of the synclinal is at a higher level in the first than the last case. In the same way the point A, where the anticlinal lines would meet if produced, is higher above the surface in fig. 35 than in fig. 36, or the whole of the bed aa is more nearly out of the ground in fig. 35 than in fig. 36.

It is plain that these appearances are the result of the vertical elevation of the beds on one side of the fault FF in fig. 34, or their vertical depression on the other side of it. The greater the throw on the downcast side the more widely will the outcrops of a synclinal curved bed be separated, and the more nearly will the outcrops of an anticlinal curved bed be brought together, while on the upcast side of the fault the reverse is the case, the outcrops of a synclinal curve will be brought together, and those of an anticlinal will be separated. When either the angle of the dip or direction of the strike of the beds vary along the course of a fault, its effect upon the position and form of their outcrop becomes equally various. This effect may be still farther complicated by a change in the amount of the "throw" of a fault in different parts of its course.

3. We have hitherto supposed the fault to run directly across the beds, or nearly so, but some faults may either, in whole or in part of their course, run obliquely to the strike of the beds, instead of directly across it, and instances may occur of dislocations even running along the strike, so as to entirely conceal some of the beds, as in fig. 37, which is a plan, where the fault FF, running directly along the strike of the beds, conceals part of No. 2, the whole of 3 and 4, and part of No. 5, as may be seen by the section, fig. 38.

If the magnitude or throw of the fault diminishes in one direction, we should have some of these beds coming out in that direction, as in fig. 39, producing a slight variation in the strike of the beds. Many other modifications may arise according to the variations in the direction of the faults, with respect to the strike of the beds, or in the amount of their "throw."

The figures represent the amount of the downthrow at each point in feet, yards, or fathoms, as the case may be.

It is possible that this bending of the beds along the line of fault may occur more than once, so that they may be thrown into undulations, and thus more than one maximum throw may be produced. This undulation, too, may also become so great that the downthrow may change sides, as is attempted to be shown in fig. 43. This actually occurs in nature sometimes, the fault appearing to die away when the beds come together, and then to set on again with a dislocation in the opposite direction. The fig. 43, however, is to be taken as a mere diagram to help the explanation, and not as an actual representation of nature, where the undulations are rarely if ever so rapid. Single lines of fracture are probably in general much more extensive than the actual dislocated spaces, since such bendings and bulgings as are here shown to be necessary to cause dislocation, would be more likely to occur near the central portions of a fracture than near its extremities.

When there is more than one line of fracture, the fact of dislocation becomes more easy to understand, since there is no difficulty in conceiving that the angle, or corner of ground included between the intersection of two faults, has been dropped down below, or squeezed up above the corresponding beds on the outside of them. In the plan fig. 44, let \(ab\) and \(cd\) be two faults meeting in the point \(b\), the included part \(d\) may be either depressed below, or raised above \(abc\). Even in this case, however, the beds on one side or other of the faults must be bent up or down in the direction of \(ed\), because, as the two faults end or die out at \(a\) and \(c\), the whole of the beds must be on the same level there, and one part or other must change that level in proceeding in the direction \(ed\).

There is a modification of this case shown in fig. 45, where we have one long continuous fault \(AB\), with one or more lateral branches, \(cd\), \(ef\), \(gh\), &c., proceeding out of it, or leading into it, as we may choose to consider them, and either on one or both sides of it. In this case, while the whole mass of ground is thrown down on one side of \(AB\), with respect to the other, the particular portions between \(cd\), \(ef\), or the corners between any one of them and the main fault may have additional minor dislocations of their own.

In fig. 41 some beds are supposed to be cracked by the fissure \(ab\), and the part \(e\) to have been bent down, but we might just as easily have supposed the part \(d\) bent up, or both operations to have taken place simultaneously. Without some such bending, no dislocation could have occurred.

Such "single line faults" have been produced, as is proved in coal-mining. They generally have one, but sometimes more points of maximum "throw" near the centre, and gradually diminishing each way till they die out. Not unfrequently they split towards one or both extremities, as is shown in the plan, fig. 42, in which the main fault \(ab\) is seen to be split into three at one end and two at the other. A long powerful fault is often composed in the whole, or part of its course, of a number of parallel fissures very close together, along a narrow band of country, breaking the rocks into a corresponding number of steps, as in fig. 46, which either "throw" all in the same direction, or having some steps in opposite directions, produce a balance of "throw" in one direction, so that it is treated as one wide fault.

In order to have any mass of beds entirely cut off on all sides from those that surround them, and wholly depressed below, or raised above them on every side, it is obviously necessary that we should have at least three straight faults, or one or two curvilinear faults surrounding the fractured piece of ground. Such dice-like masses of ground let in bodily among a strange set of beds do occur in nature, though they are very rarely met with.

Faults and fissures are sometimes vertical, as at A, fig. 47, but more commonly inclined at various angles, even so low in some instances as 20°, as at B, fig. 47.

In speaking of the inclination of a fault, it is better not to use the term "dip," as if it were a bed, but to adopt that of "hade" or "underlie." In inclined faults,—and it almost always happens that faults are inclined,—there is one nearly invariable rule, which is, that the fault "hades" or "underlies" in the direction of the downthrow.

As a corollary of this rule also, another equally important one may be stated, namely, that however inclined may be the fault, no part of any bed will ever be brought vertically under another part of it, and therefore superior beds can never be brought by any fault under those originally below them.

Small exceptions to these rules may sometimes occur in rare instances; when they do, the fault that produces them is called a reversed fault.

In fig. 47, for instance, the fault between B and C hades under the downcast piece of the bed aa; and it is ob-

1 In the neighbourhood of Bunnahon, in county Waterford, detached masses of old red sandstones are let in among the Silurian rocks, so as to be entirely inclosed by them on every side. sides of the piece I, would have to be overcome. We are not aware, indeed, of any case similar to this having been even supposed by any one.

Professor H. D. Rogers, in his paper on the "Laws of Structure of the more disturbed Zones of the Earth's Crust," (Trans. Royal Soc. Edin., vol. xxi., p. 3), in describing faults along the axes of anticlinal curves, where inversion has taken place on one side of the anticlinal, speaks of the uninverted part of the anticlinal having been thrust up the inclined plane of the fault, over some of the inverted beds, as in fig. 51.

![Fig. 51. Inversion, with reversed faults.]

Professor Rogers does not allude to the fact of this form producing a reversed fault, nor is it quite clear in his paper whether the structure thus described has been absolutely observed in sections, or is merely introduced hypothetically as an explanation of certain puzzling phenomena. If actually observed, a detailed description of the locality would be very interesting; neither are we prepared to combat the hypothesis, if it be one, since it is just in such greatly disturbed districts that "reversed" faults are likely to occur.

Another published example of a reversed fault on a large scale is given in the Rev. Professor Haughton's paper on the "Mining District of Kenmare" (Journal Geological Society, Dublin, vol. vi., p. 2). In this case also, no notice is taken of the fault, as drawn, being a reversed one; and though it is in a highly disturbed district, and running parallel to the axis of a synclinal curve, yet as its plane does not coincide with that axis, but cuts across it obliquely, and buries some of the upper rock under the lower in a very peculiar manner, it appears to us a far less probable form of fault than that described by Professor Rogers.

Faults ordinarily extend indefinitely downwards. We cannot comprehend the possibility of fracture and displacement having taken place in any uncontracted set of beds without all those below having been equally disturbed, unless we come to a part where another fracture occurs, producing an equal amount of displacement in an opposite direction. This junction between two opposite faults produces what is often called a "trough," the faults being called a "pair of trough faults." The opposite faults of a trough may be either unequal in "throw," as ac and bc, in the trough A, or equal, as de, fe, in trough B. In the former case, the displacement affects the whole mass of the sur-

![Fig. 52. Trough faults.]

rounding rock, as may be seen by tracing the bed X through the dislocations; in the latter case, it only affects the mass B, which is included between the faults. In the latter case we may see that the bed X on the outside of the trough B is on the same level on both sides.

The mode of explanation of these trough faults that seems to us the most probable, if not the only one, is the following:

![Fig. 53.]

Suppose the beds AA, BB, &c., to have been formerly in a state of tension, arising from the bulging tendency of an internal force, and one fissure, FE, to have been formed below, which on its course to the surface splits into two, ED and EC, as in fig. 53. If the elevatory force were then continued, the wedge-like piece of rock W between these two fissures, being unsupported, as the rocks on each side separated, would settle down into the gap, as in fig. 54. If the elevatory action were greater near the fissure than farther from it, the single fissure below would have a tendency to gape upwards, and swallow down the wedge, so that eventually this might settle down, and become fixed at a point much below its previous relative position. Considerable friction and destruction of the rocks, so as to cut off the corner gh (fig. 54) on either side, would probably take place along the sides of the fissures, and thus widen the gap, and allow the wedge-shaped piece W to settle down still farther.

![Fig. 54.]

When the forces of elevation were withdrawn, the rocks would doubtless have a tendency to settle down again, but these newly included wedge-shaped, and other masses, would no longer fit into the old spaces, so that great compression and great lateral pressure might then take place.

The reader must recollect that the figs. 53 and 54 are mere diagrams to assist his comprehension, and not actual representations, in which there would necessarily be introduced a much greater amount of irregularity and complexity. This may be seen by an inspection of fig. 55, which represents the commencement of a trough fault, on the small scale, in the middle of the thick coal of South Staffordshire. This was carefully drawn to scale by a competent observer, Mr. Johnson of Dudley, and will show that fractures similar to those just spoken of actually occur in nature, and what are the circumstances attending them. (See Records of the Geological Survey, vol. i., part 2, p. 313.) In this fig. the coal CC has apparently once been more completely arched, and on the cessation of the elevatory action, has tended to settle down again. The insertion of the wedge-shaped piece of the upper beds A has prevented its gaining the original horizontal position; but the Mr W. Hopkins has shown us that fractures in the crust of the globe have taken place in obedience to certain mechanical or physical laws. If a tract of country of indefinite length and breadth, composed of a set of nearly homogeneous beds, supposed to be originally horizontal, and nearly equally tenacious all over, be acted on by an expansive force from below, such as an elastic gas or a molten fluid would exert, those beds will be strained so as to tend towards bulging upwards, until a number of parallel fissures are formed, commencing at points below the surface, and running up to it. They may be crossed either then or subsequently by another set of parallel fissures at right angles to the first set. These are the normal results which may, in actual fact, be complicated by many irregularities arising from conditions different from those which were assumed.

It seems to follow from these results, that for displacement to have taken place among the fractured masses, two or more faults should meet below, so as entirely to sever the masses from each other, and allow of unequal motions being communicated to them, or that faults should gradually end downwards on the surfaces of highly-curved, undulated, and contorted beds.

The intrusion of igneous rock will in some instances increase the dislocations; but the student must be on his guard against attributing to local intrusion of igneous rock effects of elevation, or contortion, or fracture, which are due probably to very widely-extended accessions of heat expanding large masses of rock of all kinds simultaneously over great countries, and the subsequent contractions when that heat is diminished or taken away. Small local intrusions of igneous rock act principally as stays and wedges to prevent the dislocated beds settling back into their former places, but can rarely be looked on as the actual causes of disturbance. When we come, indeed, to consider large intrusions of great granitic masses into the rocks above them, we see a fertile source of dislocation, first, by the expansion of the superior rocks from the mere protrusion of the bulk of the molten mass, and afterwards from contraction in consequence of the cooling of that mass which contraction, as we have already seen (chap. ii., § 3,) might amount to even one-fourth of its bulk.

Where any large mass of matter, too, has been ejected over the surface of the ground, the withdrawal of its bulk will have tended to leave a void space in the interior, which, if it were not filled up with other igneous matter, would be followed by subsequent sinkings and dislocations of the rocks over it.

VI.—MINERAL VEINS, THE RESULT OF CAVITIES FORMED BY DISLOCATIONS.

In studying faults, our object was principally to describe their effect in dislocating the beds which they traverse; the form, the width, and the extent of the fissures themselves was only noted as affecting the beds; and the contents of the fissures, when any spaces or cavities existed between their walls, was scarcely spoken of at all.

It was shown, however, that where faults traversed hard rock, they must necessarily, unless the fissure be a perfect plane, be more or less open in places, some portions of their walls being kept apart by the protuberances of other parts. It was said also, that fragments of the fractured rocks were often found in the fissures, and these fragments must necessarily contribute to keep the sides of the dislocated portions apart from each other.

Now, in some districts, these more or less open faults and fissures have become the repositories of minerals that have been subsequently introduced into them.

These minerals are usually in a crystalline form, and consist commonly of quartz, calc, heavy, fluor, and other spars, together with the ores of one or more metals, such as lead, copper, tin, iron, zinc, antimony, mercury, silver, gold, and platinum.

Fissures containing minerals in this form are called "mineral veins," or "lodes."

Spars and ores, however, are not confined to fissures such as we have been describing. They are found occasionally in all kinds of cracks and cavities, whatever may have been the cause of the hollows, and even in little nests, lining detached holes, often no larger than the fist, and entirely surrounded by solid rock. They are found also in long pipe-like hollows in limestone, which are due apparently to the corroding action of acidulous waters; in the interstices between beds and joints similarly or otherwise enlarged, as well as in cracks, resulting from desiccation in the middle of nodules. Those in pipe-like and irregular cavities are called "pipe veins," as distinguished from "lodes," which are also called "rake veins." Wherever, indeed, permanent hollows and interstices of any kind, size, shape, or origin, exist in hard rocks, and where they are kept open for great periods of time, there appears to be a possibility, and, in particular districts, a probability, of crystallized minerals, spars, and ores, being formed in them.

That they occur most frequently and in most abundance in such fissures as we have described under the head of faults and dislocations, is due, probably, to the great range and extent of those fissures, and to the fact of their necessarily having many hollows and cavities throughout that extent wherever they traverse hard and solid rocks.

There is also another reason why the quantities of crystallized minerals should be greater in such fissures than elsewhere, and that is, that any subsequent disturbances in the mass of the rocks will tend to produce subsequent motions along the lines of the old fissures, and thus form additional cavities, which may be filled up by fresh accretions of spars and ores. (See Geological Report on Cornwall, &c., by Sir H. T. De la Beche, p. 344, &c.)

We have already said that faults, and therefore mineral veins, are sometimes perpendicular, but more often inclined. This inclination, however, is generally a high one—more often above than below an angle of 45°. Now, any subsequent fractures and dislocations which may traverse the original faults or veins, will shift or displace their course at the surface of the ground, just as if they were similarly inclined beds. What has been said, therefore, at p. 172 as to the apparent lateral shifting of inclined beds being due to vertical elevation or depression, will also be true with regard to the intersection and shifting of veins. If, in figs. 31, 32, and 33, aa be a vein instead of a bed, the explanation of the positions at the surface of the various parts of it will equally hold good.

In studying the intersection of fissures or veins, however, it may happen that the apparent shifting at the surface may not be due to any dislocation of one vein by the other at all. They may both have been produced simultaneously, one or the other not having been continued exactly in the same straight line. It may happen, too, that instead of bb' having cut through and shifted ad (fig. 56), bb' may have been the first formed, and that when ad was subsequently produced, it ran along bb' for a certain space before it was continued into the "country" on the other side of it.

Great care, therefore, is necessary in examining the intersections of mineral veins before deciding on the relative age or on the exact nature of the dislocations that have caused or affected them. Having said so much here as to the connection of mineral veins with faults and dislocations, we shall defer their further consideration to a future place.

VII.—CLEAVAGE: ANOTHER RESULT OF THE PHYSICAL FORCES BROUGHT TO BEAR ON ROCKS SUBSEQUENT TO THEIR CONSOLIDATION.

We have now described three kinds of divisional planes traversing rock—those, namely, which we might call congenital, or planes of lamination and stratification; those which are necessarily resultant on consolidation or joint planes; and those which we may term accidental, such as fissures, faults, and veins. There is yet another kind to be described, which we may call superinduced planes of division; and these are planes of "cleavage" and "foliation."

By "cleavage," or "transverse" or "slaty cleavage," as it is sometimes called, we understand a tendency in rocks to split into very thin plates, having a certain given direction over wide areas independently of any original lamination or stratification of the rocks. It is a structure which is most especially remarkable in clay slate, but is sometimes apparent in sandstones and limestones. Where it exists it is always most perfect in the finest grained rocks, splitting them into an indefinite number of thin leaves or plates, perfectly smooth and parallel to each other. The coarser the rock, the fainter, the wider apart, and the more rough and irregular do the cleavage planes become.

This cleavage may either coincide with the original lamination of the rock, or cut across it at any angle. When it cuts across the bedding of the rock, the original lamination, or tendency to split along the planes of deposition, is generally obliterated, the laminae being sealed up, or, as it were, welded together. This cementation of the original plates of lamination is not quite invariably the case. I have met

with at least one instance where the rock, an indurated shale, split as readily along the original lamination as along the cleavage planes, and was thus minced into long, needle-shaped spicules of slate. (Report of Geological Survey of Newfoundland, p. 75.)

Transverse cleavage in sandstone usually divides the rock into coarse slabs only, the upper and under surfaces of the sandstone often breaking into dog-toothed indentations. In traversing conglomerates, the cleavage planes leave the pebbles standing out in relief, and do not cut through them as joint planes do. (Professor Sedgwick.)

Cleaved limestone generally has the original bedding greatly obliterated and obscured; the slabs are thick and uneven, and their surfaces often coated by argillaceous films, sometimes giving to the cleavage the exact appearance of bedding. Among trap rocks, some very fine-grained feldstones are occasionally affected by cleavage, and fine-grained feldspathic and hornblende ashes are often so affected.

The direction of cleavage planes is generally constant over considerable areas, retaining the same compass bearing through whole mountain chains, or across large countries, without paying any regard to the contortions and convolutions of the rocks. One of the best examples of this steady direction in the strike of the cleavage planes is the south of Ireland, over the whole of which, from Dublin to the Mizen Head and the Dingle Promontory, the direction of the cleavage never varies 10° from E. 25° N., whatever rocks it traverses, and however different these rocks may be in lithological character and geological age.

This steady direction generally coincides with that of the main lines or axes of elevation and disturbance which traverse the district, and consequently with the "strike" of the beds.

The inclination of the cleavage planes varies from perpendicularity to within a few degrees of horizontality, but has no apparent reference to the dip or inclination of the beds.

In passing through beds of different texture, the cleavage planes often vary their angle a little, having a tendency to strike more perpendicularly across the coarser than the finer grained beds. When the inclination of the cleavage planes... Geology, and that of the original planes of lamination become nearly coincident in any locality, they sometimes appear to coincide entirely, as if the cleavage went a little out of its way, as it were, to coincide with the bedding.

The finest and largest roofing-slates seem to be those of a bluish gray or pale green colour. Where they become either very red or quite black, they are more brittle, and more readily decompose, owing probably to the presence of peroxide of iron in the one, and carbonaceous matter in the other. Bands of colour, such as faint red, green, white, or gray, may sometimes be observed on the sides of slates, often coinciding with slight changes of grain or texture. These, which are called the "stripes" of the slate by Professor Sedgwick, mark its original stratification. The bands in the block, about 18 inches in height, which is figured in fig. 57, show this stripe very well. The white bands are pale greenish, or grayish fine-grained grit—the intermediate parts being purple slate of various tints and degrees of colour. They are the original laminae of deposition of the rock. Irregular blotches, however, of different colours, occasionally occur; and sometimes even pretty regular broad bands of colour are to be seen, which do not coincide with the bedding, but go sometimes directly across it, as proved by beds of sandstone interstratified with the slate. Care must be taken, therefore, in field observations, not to rely too implicitly on mere bands of colour in slate colours.

Professor Sedgwick was the first to systematically observe and describe the phenomena of slaty cleavage. His observations will be found in the Transactions of the Geological Society, vol. iii., on The Structure of large Mineral Masses, and also in his Introduction to a Synopsis of the British Palaeozoic Rocks, 3d Fasciculus, p. 33. In the latter, he gives the following as the results at which he had arrived:

1st. That the strike of the cleavage planes, when they were well developed, and passed through well-defined mountain ridges, was nearly coincident with the strike of the beds.

2nd. That the dip of these planes (whether in quantity or direction) was not regulated by the dip of the beds, inasmuch as the cleavage planes would often remain unchanged, while they passed through beds that changed their prevailing dip, or were contorted.

3rd. That where the features of the country or the strike of the beds were ill-defined, the state of the cleavage became also ill-defined, so as sometimes to be inclined to the strike of the beds at a considerable angle.

4th. Lastly, that in all cases where the cleavage planes were well developed among the finer slate rocks, they had produced a new arrangement of the minutest particles of the beds through which they pass.

One of the most striking effects of cleavage is the distortion it produces on fossils or other small bodies embedded in the rocks, lengthening and pulling them, as it were, in the direction of the cleavage, and contracting them in the opposite direction. Relying on these facts, which were first distinctly noticed by Professor John Phillips, Mr Sharpe attributed the production of cleavage to the action of great forces of compression squeezing the particles of rock in one direction and lengthening them in the opposite. (Quarterly Journal Geological Society, vol. iii., p. 87.) Mr Sharp believed that the fossils were lengthened in the direction of the dip of the cleavage, but Professor Haughton believes this to be impossible, and that the lengthening must always be in the direction of the strike of the cleavage. Mr Darwin also, from his observations in South America, formed similar ideas as to the origin of cleavage, and speaks of cleavage planes as being probably parts of great curves, of such large radius as that any portions of them that can be seen at one view appear to be straight. More recently, Mr Sorby, resting on the fact of beds of sandstone which occur in slate being contorted, and their dimensions being contracted at the sides, and expanded at the tops and bottoms of the curves, the axes of which curves coincide in direction with the cleavage planes, while the beds of slate above the sandstone are little or at all bent, shows that the particles of the slates must have been compressed at right angles to the cleavage planes, and lengthened along them, so as to allow of their being squeezed into the same contracted space as the sandstones, without much bending of the surfaces of the beds. (See New Philosophical Journal, 1853, vol. iv., p. 137; or Lyell's Manual, 5th edition, p. 611.)

By microscopical examination, Mr Sorby found that the minute particles of clay-slate were either lengthened in the direction of the cleavage planes, or that those minute particles, which were of unequal dimensions, were so rearranged as that their longer dimensions coincided with the planes of the cleavage.

Professor Sedgwick at one time thought that he could perceive a tendency to a symmetrical arrangement of the inclination of the planes of cleavage with respect to the axes of lines of elevation, the dip of the cleavage being inwards on each side of the mountain ranges. He afterwards, however, saw reason to abandon this conclusion. Mr Darwin speaks of the fan-like arrangements of the cleavage planes which have been described by Von Buch, Studor, and others; and Mr Sharpe says that this apparent fan-like arrangement is due to parts of two contiguous curves meeting where their adjacent sides become perpendicular. But we must refer the reader to his papers on this subject, in the third and fifth volumes of the Journal of the Geological Society before quoted, and in the Philosophical Transactions for 1852. A second cleavage plane cutting across the first at right angles, and also across the bedding, is described by Mr Sharpe in his second paper on cleavage in the Geological Journal, vol. v., p. 3, and was also long before observed and mentioned by Professors Sedgwick, Phillips, and others. Mr Sharpe attributes this likewise to compression.

The subject has recently been investigated by Professor Tyndal, who, in a paper in the Philosophical Magazine, vol. xii., distinctly refers the origin of cleavage to the same force of compression, acting at right angles to the cleavage planes, that Mr Sorby and Mr Sharpe had referred it. Professor Haughton, in a paper in the same volume, has deduced mathematically a value for the compression of the rocks, from examining the amount of distortion suffered by fossils in some particular instances in consequence of this compression.

There seems, indeed, now little doubt that mechanical compression is the true cause of cleavage; but the whole subject requires still more accurate and detailed observations than have yet been made on it. We have seen reason to suspect—in some districts of North Wales, for instance—that subsequent movements and dislocations have affected large cleaved districts in such a way as may have altered both the dip and strike of the cleavage from their original position. Only direct observation, then, will now lead us astray, unless it be corrected by a more accurate knowledge than we yet possess of the amount and direction of these dislocations, and of their relative age compared with that of the cleavage. The dip of the cleavage, especially, is very easily mistaken, unless it be observed in very clear and deep excavations. Superficial causes have frequently affected, and sometimes completely reversed it, to very considerable depths, as may be seen in fig. 58.

When these superficial bendings of slate occur on deeply inclined ground, they may perhaps be referred to the action of gravitation on substances loosened by weathering, or the "weight of the hill," as it has been called. In other cases their origin is more obscure, and we have seen one instance in North Wales, where, on the horizontal surface of an isolated boss of rock, the slates were so sharply and abruptly bent back and laid nearly flat, and partly consolidated in that position, as to give the idea of its being due to some sudden and great force, such as the grounding of an iceberg.

Thoroughly to work out the subject of the "cleavage" of any district would require months of continuous and laborious observation in a country the geological structure of which had in other respects been thoroughly and accurately surveyed; and, with the exception, perhaps, of North Wales, no country has yet been surveyed with anything like an approach to such accuracy.

VIII.—FOLIATION.

The foliation of the schists appears to be equally a superinduced structure with the cleavage of slates. It is, however, quite clear that even if the cleavage of slates have a mechanical origin, the foliation of schist cannot be due to such a cause alone. Mechanical pressure may be readily supposed to communicate a certain mechanical texture, but cannot by itself cause a difference in chemical composition. Now, "foliation" is defined by Mr Darwin, to whom we owe the recent technical use of the term, first introduced by Professor Sedgwick, to mean "a separation into layers of different chemical composition;" while "cleavage" means only a "tendency to split" in a mass of the same composition.

Nevertheless, the folia of schist are in some districts arranged in certain given directions by compass over very wide areas. Mr Darwin says that the gneiss and mica schist of South America, for instance, have their layers or folia always arranged in a certain given direction, even for hundreds of miles. For 300 miles, at least, in the Chonos and Chiloé islands, it does not vary a point of the compass from N. 19° W. and S. 19° E. Over the eastern parts of Banda Oriental the foliation strikes N.N.E. and S.S.W., and over the western parts W. by N. and E. by S. In Venezuela, according to Humboldt, it is uniformly N.E. and S.W. (Darwin, Volcanic Islands, p. 163.)

According to Mr Sharpe (Transactions Geological Society), the foliation of the gneiss and mica schist strikes across Scotland in directions varying from N. 50° E. in the south of the Highlands to N. 25° E. in the north. The dip of the folia of schist resembles that of the dip of cleavage planes, in being much more uncertain in direction and quantity than that of the strike.

Some geologists have held that gneiss, mica schist, &c., were originally formed nearly as they are now, being the direct result of the erosion of granitic rocks, of which the quartz, feldspar, and mica were arranged in regular layers as we now find them, the only change having been a mere consolidation or induration. The perfect parallelism of these layers, however, over such wide areas as those before mentioned, would of itself be against this supposition, and in favour of the rearrangement of the particles of the rocks, in obedience to some wide and general force.

As to the nature of this force, Mr Darwin and Mr Sharpe, as well as Professor Sedgwick, agree in looking on foliation as the extreme term of cleavage,—that foliation and cleavage are parts of the same process; in cleavage, there being only an incipient separation of the constituent minerals; in foliation, a much more complete separation and crystallization." If, however, this be true, we do not see how this process can be the merely mechanical one to which we have just seen reason to assign the production of cleavage.

Mr Darwin even appears to look upon many of the great divisions of foliated rocks, which are ordinarily termed beds or strata, as merely farther results of the process, different mineral substances having been segregated from each other on the large scale.

In large greatly altered districts, however, the very amount of the alteration has so completely changed the character and texture of the rocks, that it is more difficult to detect that it is a change than in other districts, where the alteration having taken place on a smaller scale, and to a less extent, its nature may be more readily grasped.

In the S.E. of Ireland, one great mass of granite has been erupted through the clay-slates of the district, forming a continuous range of granite hills from Dublin Bay to the neighbourhood of New Ross, a distance of 70 miles. Between this range and the coast, other smaller intrusive bosses of granite make their appearance at the surface through the clay-slate rocks. The clay-slates are dark-gray, blue, or black, but sometimes pale-green, or greenish-gray, with occasionally red or purple bands. They are generally of a dull earthy texture, and without lustre. Small bands of gray siliceous grit frequently occur in them.

Wherever the granite comes to the surface, a belt of slates surrounding it is converted into mica schist, with, in some few places, beds of perfect gneiss. Crystals of garnet, schorl, andalusite, staurolite, &c., make their appearance in these altered slates in greater and greater abundance as they approach the granite. The width of the metamorphosed belt is generally proportioned to the size of the granite mass which it surrounds. Round the smaller granite bosses it is sometimes not more than 50 yards wide; round the main granite mass it sometimes reaches to two miles. It matters not through what part of the slate rocks the granite rises, or which beds strike toward the granite; they are all found to be affected in the same way as they approach it.

In going towards the main granite ridge, it is found sometimes at a distance of 2 miles from the outcrop of the granite (which is, however, much nearer probably in a vertical direction), and that the slates have acquired a "glaze," as it were, or micaceous lustre, with a soapy feel. This lustre is apparent throughout the mass when the slates are broken, and even when they are ground down into sand or powder. This micaceous resemblance increases as we approach the granite, till at last distinct plates and folia of mica are to be seen, and the whole assumes the ordinary character of mica schist, occasionally passing into a kind of gneiss.

Together with the micaceous lustre on the surface of the slates, the rocks often assume the puckered and corrugated structure of mica schist. We at one time thought that this corrugated structure might be a metamorphic one, like the foliation; but on examining localities where the small bands of siliceous grit were interstratified with the slates, we found these grit bands to be equally corrugated and puckered. The structure, then, must be ascribed simply to a mechanical force compressing the rock laterally. In the majority of instances, too, the folia of the mica schist, whether straight or puckered, were parallel to the grit bands, and therefore to the original lamination and stratification of the rock. In these instances, the micaceous folia were largest and best developed. In other cases, the foliation ran across the bedding, coinciding apparently with the cleavage, as remarked by Professor Ramsay in a similar case in North Wales. In these instances we generally found the micaceous folia short and discontinuous, being apparently interrupted by the changes of texture or composition in the original lamination of the rock. We could, however, easily conceive that where the rock was quite homogeneous, the folia of mica schist might be almost as extensive as the planes of clay-slate.

Some of the beds of gneiss in this district are obviously beds of sandstone, originally interstratified with the shales, the rocks having all the appearance of interstratified beds of shale and sandstone at a distance, and until they are broken open and found to be perfect mica schist and gneiss. Other gneiss beds are massive and thick-bedded, and containing large crystals of feldspar (apparently orthoclase) becoming quite porphyritic and completely mineralized, but still having a foliation parallel to what is apparently the original stratification of the mass, which in one conspicuous instance (near Graiguenamanagh), is nearly horizontal.

We do not think that the person most sceptical as to the fact of the metamorphic origin of mica schist and gneiss could examine the rocks bordering the southern end of the granite range in Carlow, Kilkenny, and Wexford, without becoming a complete convert to the theory. For ourselves, we can no longer feel the slightest hesitation in accepting the metamorphic origin of all those which have been described under that head in Lithology.

IX.—DENUDATION: A CONSEQUENCE OF THE ELEVATION OF ROCK.

In a previous section we have spoken of the erosive action of moving water upon aqueous rocks while in course of formation; and in treating of the formation of mechanically-formed aqueous rocks, we have tacitly assumed the fact of great disintegration and erosion of previously existing rock, in order to afford the materials of which these mechanically-formed rocks were composed. We have now also considered the general effects of disturbing forces in elevating aqueous rocks from the bottom of the sea into dry land, so far as regards the new positions into which these rocks have been thrown, and the divisional planes and dislocations which have been produced in them. It yet remains to study some other of the less immediate results of these elevating forces.

In examining the outcrop of a set of beds along the surface of the ground, either in "the field" or by aid of geological maps and sections, we must be often struck with the fact that the present terminations of the beds are not their former or original terminations. Beds rise successively to the surface, and end there abruptly, that were once obviously continued beyond or above the present surface of the ground. In fig. 20 the beds on the beach and those in the cliff are the same. It is clear that they have been cut down on the beach to their present level, and that before they were so cut down they rose upwards to the same height as those in the cliff. In the same way, those in the cliff itself, and which stretch from it into the land, formerly extended upwards to a greater height than they now do. Now in many instances we can tell how far they formerly extended upwards. In figs. 24 and 25, the anticlinal and synclinal curves into which the beds are thrown enable us to estimate the amount of this cutting down or denudation for the beds there drawn. In fig. 24 we see that beds 2, 3, 4, bend continuously over No. 1; and we should naturally conclude that beds 5, 6, 7, 8, &c., once equally extended continuously over the anticlinal A. If we doubted the fact, we should be convinced of it when we traced them in the map (fig. 25), and found them gradually meeting and continuous over the anticlinal farther towards the north.

Similarly in the synclinal curve B, though we might suppose by the section that No. 13 was the highest bed, we should find that towards the north it was overlaid by beds 14, 15, &c.; and we should be compelled to conclude that the latter had once been continuous over the whole. The dotted lines in fig. 24 would, if completely carried out, and bed 13 were represented as arching continuously over A, give us the measure of the amount of solid rock removed by denudation from above the present surface of the ground EF, so far as the beds there drawn are concerned.

It makes no material difference in this reasoning whether we suppose the spaces 1, 2, 3, &c., to represent single small beds of a foot or two in thickness, or groups of such beds, and suppose the whole series, 1 to 15, to represent a vertical thickness of many hundreds or many thousands of feet.

Neither would it make any difference in our reasoning, so far as the amount of denudation is concerned, if we were to modify our conclusions by supposing, in all those cases in which great thicknesses are concerned, that the whole mass of beds were never continuous over the anticlinal curves after the total amount of elevation had been reached. We may suppose that soon after the elevation commenced, and simultaneously with the first arching of the beds, the denuding forces began to act, that they took advantage of the very first cracks that were formed to commence the erosive process, and that long before the bed No. 1 attained its present position on the axis of the curve, more or less of the higher beds 7, 8, or 12, 13, &c., had been removed, and a surface given to the rocks more or less approximating to the surface they at present possess.

Another very clear case in which we can estimate the amount of denudation is that of an "outlier," as it is called. It often happens that a number of beds, rising at a slight angle from beneath the surface, end in a steep slope or "escarpment," as at A in fig. 59. In front of this escarpment there often rises an isolated hill as B. In descending the escarpment, we pass over the edges of the beds 11, 10, 9, 8, &c., in regular succession, and find 4 coming out from beneath them, and stretching continuously across the intermediate flat or valley, and forming the base of the hill B; and on ascending the side of B, we find the very same beds 5, 6, 7, 8, resting on each other in the same order as we saw them in the escarpment A; and at the same angle of inclination, so that the conclusion becomes irresistible that they were once continuous across the intervening space C. This space, then, is due to the erosive action which has removed the upper beds, and denuded or laid bare the lower bed No. 4, across the valley C, and for an indefinite distance on the other side of the hill B. We should feel quite certain that not only the beds 1, 2, 3, 4, but also 5, 6, 7, &c., had stretched across this space formerly, and had also extended beyond the hill B for some indefinite distance in the direction of D. This latter conclusion we should in many cases find confirmed by the occurrence, at a distance perhaps of many miles beyond B, in the direction of D, a locality where the beds dipping in an opposite direction from that Geology. In fig. 59, these very same beds (1 to 8 of fig. 59) are brought in again in the very same order and with exactly the same character as before (fig. 60). In some cases, such a little isolated basin forms the only remaining patch of

![Fig. 60. Ostrich basin.]

the beds left in this new district, by having been dipped down below the level of the surface formed by the denuding agent, and remaining as a monument of their former extension over the wide intervening space between this new locality and that of the escarpment and outlier before mentioned.

Geological maps of large countries often enable us to prove by such reasoning as this the former extension of a great mass of beds over very wide areas, and consequently the very large amount of denudation that has taken place. In many instances we can show the geological date of this denudation; that is, we can prove it to have taken place before the time when such and such beds were deposited, the age of which is known, and which we find lying across the edges of the denuded beds. This leads us to the next subject of unconformability. We must, however, always guard ourselves against attributing to the last period of denudation that occurred, with respect to any set of beds, effects, a large part of which perhaps took place at previous periods. Almost all lands have risen from the bed of the sea, not once only, but many times, having passed through many periods of alternate elevation and depression, suffering denudation at each passage through the upper surface of the sea, and during each period of existence as dry land. It appears probable, from the observations of Mr Darwin and others, as also from the very nature of the case, that a period of slow and gradual elevation is the one most favourable to the action of the destruction of pre-existing rock, or to denudation, while a period of depression is that most favourable to the deposition and formation of new rocks on the surface of the old. Many districts, however, might be depressed without being covered by the deposition of new rock, or by so thin a skirt of it, that it might be easily stripped off during a subsequent elevation; and in every new period of elevation the erosive forces would most probably act again upon their old lines, deepening former hollows, and thus intensifying the previous features of the old lands on their re-emergence from the sea.

X.—UNCONFORMABILITY: THE RESULT USUALLY OF ELEVATION, DENUDATION, AND SUBSEQUENT DEPRESSION.

When one set of beds have been elevated and denuded, and another set of beds are deposited on this denuded sur-

![Fig. 61. Unconformable beds.]

face, the two sets are said to be unconformable to each other. In fig. 61 the arched and denuded set of beds A are covered by the unconformable set of beds C. Whenever two sets of beds lie at different angles of inclination, they are apparently or obviously unconformable. In fig. 61 this discordance of inclination is seen strikingly at either end of the figure, but if we confined our attention to the central part d, we should not perceive any unconformability.

Beds, then, may repose apparently at the same angles over considerable spaces, and yet be unconformable in reality. In fig. 62, again, two sets of beds, A and C, are shown, which are both horizontal, A ending in a broken cliff, with C abutting directly against it in that part, although it rests in apparent conformity on A at the point d.

The essential point in unconformability is, that the upper group of beds shall rest upon different parts of the lower group at different places, and this could not happen without previous elevation and consequent denudation having affected the lower group. It proves, then, the lapse of a considerable interval between the deposition of the two sets of beds.

Now, although this interval may have been occupied by the process of destruction going on in one locality, there is no reason why production may not have been taking place at the same time in another locality. Whenever, then, we find two sets of beds unconformable to each other, we must suppose that there is a set of beds wanting there which may elsewhere be found, and that where they are found there will be probably no unconformability. If fig. 63 re-

![Fig. 63. Three conformable sets of beds, A, B, C.]

present the state of things at one locality, where the three sets of beds ABC were deposited in regular continuous succession, figs. 62 or 61 may represent the other localities, where the interval here occupied by the deposition of B was there employed by the forces of elevation and denudation in the destruction of a previously existing part of A. It is even quite possible that the materials which were used in the locality represented in fig. 63 in the composition of B, were partly derived from this destruction and breaking up of a portion of A in one of the other localities, and that we may accordingly find in B pebbles or angular fragments of A.

XI.—OVERLAP: THE RESULT OF DEPRESSION, WITH OR WITHOUT PREVIOUS DENUDATION.

There is a minor degree of unconformability to which the term overlap is applied. This consists in a greater ex- stances have been the result of a more partial deposition in the lower beds, from the defect of material or other cause, but in other cases it has been the result of the gradual depression of the old land, and the consequent extension of the area of water in which alone deposition can take place.

While unconformability, therefore, proves an elevation and denudation, and an absence of continuous deposition, overlap may take place in a perfectly continuous series, merely proving the fact of a depression of the area contemporaneously with that deposition.

**CHAP. VII.—PETROLOGY OF THE IGNEOUS ROCKS.**

We will now consider the general forms and modes of occurrence of the principal kinds of igneous rock, and their relations to the aqueous rocks. We have previously spoken, under the head of Lithology, of the different kinds of igneous rock, and shown that these differences partly depended on the difference of their chemical composition, and partly on the texture resulting from the physical circumstances—as pressure and rate of cooling—under which their consolidation took place. The granitic rocks, or those which are most completely crystalline and most thoroughly saturated, as it were, with silica, cooled slowly and under great pressure, that is to say, at some considerable depth in the interior of the crust of the globe.

The volcanic rocks, on the other hand, were consolidated at the surface, while the intermediate and variable class which we have called trapeze may have been solidified under various and intermediate conditions.

**I.—FUNDAMENTAL GRANITE.**

As a matter of fact, it has been found that in all parts of the globe, wherever the base of the aqueous rocks has been brought up to the surface and exposed to view, that base rests upon granitic rocks. By the "base of the aqueous rocks" is meant the lowest aqueous or sedimentary rocks known in the particular locality, whatever may be their age, whether they be some of the oldest known rocks, or whether they be of a much later date than those, and whether they retain their original characters unaltered, or have been metamorphosed into mica-schist, gneiss, or any similar rock.

It is by no means intended to assert that the converse of this is true, and that wherever granite is found at the surface, there the lowest of all known rocks, or even the lowest rocks of that particular locality, will be found resting on it. On the contrary, we shall show presently that granite frequently comes through great masses of rock, without bringing them up along with it. But at every place where any rock does make its appearance at the surface from underneath the lowest of the stratified rocks known in that locality, that rock is a granitic one; and wherever any large mass of granite comes to the surface, we have no reason to believe that any other rock but granite would be found underneath it. We do not here speak of any veins, or intrusive dykes or sheets of granite, but of large, widely extended masses. In short, we have every reason to believe that if we pierced vertically downwards into the earth at any part of its surface whatever, we should eventually come either to granite or to yet molten and unconsolidated rock, which on cooling would form granite. Again, in many parts of the world granite is found occupying large areas of the surface; and we have no reason to suppose that any other rock but granite would be found under those surfaces, although, if we sank deep enough, we might perhaps come eventually to red-hot granite, and ultimately to yet molten granite. These facts and these opinions have naturally led many early geologists to the conclusion that the earth was once a molten globe of fiery matter, and that on cooling there was formed about it a primeval crust of granite; and they hence inferred that much of the granite now to be found at or near the surface was actually part of this primeval crust. At one time, indeed, it was held that all granite had this primeval character; but this notion has long been exploded, since intrusive, and therefore subsequently consolidated masses of granite, have been found penetrating rocks of almost all ages in different parts of the earth.

Now the hypothesis of the earth having once been a molten globe of fiery matter is one for which more or less good argument may perhaps be brought forward; but it is one with which the geologist has properly little or nothing to do. The geologist may grant the probability or possibility of this molten globe having existed, cf its having cooled down till a granitic crust was formed about it, of the temperature having been gradually lowered till the existence of water and air become possible upon it, and yet maintain that no part of this primeval crust is now in existence, and that none of the rocks now open to our observation can date back their formation to this quasi-fabulous and mythical age of the earth, this pre-historic or pre-geological period of its duration.

Whatever may have been the nature of the primeval crust of the globe, that crust had been more or less completely destroyed and remodelled by the erosive action of water, and the remelting action of heat, before the commencement of even the earliest of our geological periods. The very lowest of the unaltered stratified rocks of which the age is known, namely, the Cambrian of North Wales and Ireland, are made up of indurated clays, sands, and gravels, which were derived from the waste of previously existing stratified rocks, exactly like themselves. (Professor Ramsay.) The crust of the earth, then, was, before that earliest of our periods, made up of stratified and unstratified aqueous and igneous rocks, as it is now made up of them. Just so much of these earlier rocks are preserved to us as have not been since destroyed by the action either of fire or of water. Over very large areas, very early rocks, having been attacked from above, have been eroded and destroyed by the action of water; and the old base on which they rested has been denuded, and is either now exposed at the surface, or has been re-covered by other rocks subsequently deposited upon it. Over very large areas, very early rocks having been attacked from below, have been so baked, so altered and metamorphosed by the action of heat, and by the many physical and chemical forces which heat has set in motion, as to have been altogether transformed from their original state, and many of both aqueous and igneous origin actually remelted down perhaps, and re-absorbed into the molten masses of the interior, in which they either still remain as molten rock, or from which they

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1 If we were inclined to speculate on such a state of things as the first cooling of the crust of a molten globe, in which the expansive power of heat must have been acting intensely even at the surface, we might perhaps reasonably doubt the possibility of so dense a rock as granite being formed upon that surface. Porous trachyte, pumice, and obsidian, would occur to us as more probable productions than granite. may have been subsequently reconsolidated as newer igneous rock. Some ancient rocks have been in other areas spared by both these processes; but as these processes are continually going on, and continually shifting their areas of action, it is clear that, in proportion to their antiquity, all rocks must have been more or less affected by them, and that we can reason back to a period in the earth's history, the coeval rocks of which have only one or two undestroyed or unaltered areas still left upon the globe; and going one or two steps still farther back, we arrive at a period of which none of the coeval rocks can remain in their original recognisable state.

Dismissing, then, all speculations as to the primeval crust of the globe, and the primitive character of granite, let us come to what we know to be true.

II.—INTERNAL HEAT OF GLOBE.

That the earth has a great internal heat, is rendered almost certain by the following facts:

1. The specific gravity of the globe is, according to the old observations, about 5.0, or according to the recent experiments of the Astronomer-Royal, Mr Airy, about 6.7. Now, the specific gravity of granite varies from 2.6 to 2.9; that of basalt is about 3.0; that of rock in general is from 2.5 to 3.0. The earth, therefore, is more than twice as heavy as it would be if made of any known rock, such as that rock appears at the surface. The pressure of gravity, however, would render any such rock, as granite, for instance, much more than twice as dense as it is at the surface long before it reached the centre. We should expect, then, that the globe would have a much greater specific gravity than 5 or 6, if it were not for some expansive force in its interior counteracting the pressure resulting from gravitation. We know of no such force except that of heat.

2. As a matter of direct observation, it is found that in all deep mines the temperature of the rock increases as we descend, at the rate of 1° Fahrenheit for every 50 or 60 feet of descent after the first 100. This is the case in every part of the globe, and in all kinds of rock.

Deep springs also, and wells, such as the deep Artesian well of Grenelle, at Paris, are always found to have a high temperature. At Grenelle, the water brought from a depth of 1798 feet has a constant temperature of 81°7' of Fahrenheit, while the mean temperature of the air in the cellar of the Paris Observatory is only 53°. Very accurate and careful observations have lately been made by M. Walferdin on the temperature of two borings at Creuzot, within a mile of each other, commencing at a height of 1030 feet above the sea, and going down to a depth, the one of 2678 feet, the other about 1900 feet. The results, after every possible precaution had been taken to ensure correctness, gave a rise of 1° Fahrenheit for every 55 feet, down to a depth of 1800 feet, beyond which the rise of temperature was more rapid, being 1° Fahrenheit for every 44 feet of descent. (Cosmos, May 15, 1857.)

Hot springs are usually found to proceed from great faults or fissures which penetrate deeply into the crust of the globe.

3. As another result of direct observation, we may state that all igneous rocks proceed from below upwards, coming out of the interior of the earth; and that, as just observed, whenever we are able to see the actual base of the aqueous rocks in any district, we find them reposing upon cooled igneous rocks, generally granite, and that ex tertia peri-

bus, the lower the rocks, or the deeper they have formerly been buried, the more marks do they bear of having been subjected to a great heat.

We may look, then, upon the great internal heat of the globe generally as a fact pretty well established; and it appears that if the increase of heat towards the centre goes on at the same rate that it does near the surface, all water would be boiling at a depth of 9000 feet under the British Islands, and that at the comparatively small depth of 20 or 30 miles, the heat would be sufficient to fuse any of the substances we know at the surface.

There are said to be, however, certain general astronomical and physical considerations which make against the supposition of the earth's being a molten fluid mass, with only a slight external crust, and render it probable, that, however intense the temperature, the mass is still solid, either entirely or in part, to a very great depth into the interior.

In this case, it appears that the molten masses which have formed, on cooling, the igneous rocks we are acquainted with, either proceed from detached lakes of fiery liquid, or were rendered fluid by some special and locally acting circumstances.

Speculations, however, on the general state of the interior mass of the globe, although interesting, have, like those on its primeval condition, little theoretical and no practical importance; and as we shall be for ever probably condemned to remain in ignorance concerning it beyond a few general facts such as those before mentioned, they need not occupy more of our attention.

III.—POSITION AND FORM OF GRANITE.

Granite generally makes its appearance at the surface in large masses, occupying considerable areas, and extending for a great but unknown depth into the interior. Veins of granite, often branching and crossing each other, sometimes proceed from these masses, penetrating the adjoining rocks; and dykes, or wall-like sheets, of granite-rock are frequently found in their neighbourhood, running sometimes for several miles in straight lines through other rocks.

Smaller bosses of granite are likewise not unfrequent in such districts, apparently the tops and eminences of larger masses that are still concealed below.

Granite generally forms high mountainous ground, and hills composed of it have commonly a heavy rounded outline and sombre aspect. Sometimes, however, granite is found as the surface rock over considerable spaces of low gently undulating ground, in which case the plain is commonly diversified by small rounded knobs and bosses of rock.

Granite is also found not unfrequently as the rock form-

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1 Mr W. Hopkins gives 800 miles as the minimum thickness of the solid external crust of the globe. Professors Hennessy and Haughton, however, and also, I believe, Professor Jollett, dissent from a part of the reasoning on which that conclusion is based, and think that no certain conclusion can as yet be arrived at respecting the thickness of the solid crust of the globe. (See Papers in Phil. Trans., and in Trans. of R. I. Academy.) When it forms the true axis of a mountain mass, the rocks which rest upon it dip from it in every direction, and the lowest of the stratified rocks are found nearest to the granite, as in fig. 65, where G is a mass of granite forming the axis of a range, and 1, 2, 3, are the stratified rocks dipping from it in each direction, the lowest or oldest, No. 1, being next to the granite, and the highest or newest, No. 3, the furthest from it. This central and fundamental position is the one usually assigned to granite where it appears in a mountain chain. Without attempting to deny that it frequently does hold this position, we are yet rather inclined to doubt whether it has not in many cases been assigned to it as a matter of course, without adequate investigation. We are disposed to suspect that the rocks nearest the granite having been most altered, and the most altered rocks having been assumed to be the oldest or lowest, this position may often have been taken for granted instead of proved.

We know, at all events, that in many cases granite, where it occurs as the constituent of a mountain range, and as the geographical axis of such a range, is not the true geological axis, insomuch as it does not bring up with it the lowest rocks of the country, and has not the central and fundamental position, nor has it exercised the elevatory action assigned to it in fig. 65.

The granitic district in the S.E. of Ireland, extending from Dublin Bay to near New Ross in county Wexford, is one of the largest and most persistent masses of granite in the British islands, being 70 miles long, and from 7 to 17 miles wide. There were in this district at least two great geological formations, each consisting of slates or shales and sandstones, and each several thousand feet thick, at the time of the intrusion of this granite. These two formations are known as the Cambrian, which is the lowest or oldest, and the Lower Silurian, which rests unconformably upon the Cambrian. Now in no instance is any part of the lower or Cambrian formation found reposing on or coming against the granite at the surface, though it does come to the surface in some places within 2 or 3 miles of the granite, as shown in fig. 66.

The Silurian rocks, however, have been broken into, and lifted and altered by the granite, which has sent veins into them, as in fig. 67; and we are compelled to suppose, therefore, that the granite must have come through the Cambrian rock below, before it can have penetrated into the Silurian rocks which now rest upon it. Neither, although the main direction of the granite is parallel to the general strike of the rocks and principal lines of disturbance in the district, does the eruption of the granite seem to have had much effect on the general elevation of the country, but simply to have partaken of it, along with the other rocks, and to have had its direction governed by the direction of the forces of disturbance that were acting at the time of its intrusion. The Silurian slates, which are frequently vertical and greatly contorted over all the district, often appear to dip at or towards the granite, at a distance of about 2 or 3 miles from its present surface boundary, and to have been only so far affected by the proper elevatory action of the granite as to be crumpled up or dog-eared against it for a short distance close upon its flanks (see fig. 66).

If we passed from Ireland into Cornwall and Devon, similar conclusions could be drawn from the relations of the granitic masses there with rocks of a still newer date, namely, with those called Carboniferous and Devonian. The granite penetrates and alters rocks of both those periods, and is therefore newer than both. It has not, however, by its irruption brought up the lowest rock, namely, the Devonian, everywhere on its flanks. On the contrary, where it cuts into and alters the Carboniferous rocks, we are compelled to suppose that it has passed though and left behind the Devonian. Neither does the granite of Cornwall and Devon appear to have acted in any sense as a geological axis or centre of elevation, but simply to have partaken with the rocks of the district of whatever disturbances occurred during or since its intrusion; and the granitic veins appear to have been shot into the cracks and crevices of the rocks, which were opened for them by those disturbances, and not to have made any of those cracks and fissures for themselves.

In other parts of the world, as has been said before, granite is found in the same way bursting through, sending veins into, and altering rocks of still newer date, rocks of what are called the Secondary periods, and rocks of what are called the Tertiary periods; and granite must be forming now wherever molten rock of the proper chemical composition is cooling under the requisite physical conditions, that is, deeply seated under the pressure of great masses of other rock.

It is doubtless true that granite is found more frequently associated with the older rocks than with the newer; in other words, with the lower rather than the higher rocks. The reason of this, however, is clear from the very fact of the source of granite being in the interior of the earth. Granite, in order to reach the higher, must pass through whatever lower rocks there may be in the way. Many eruptions of granite may have proceeded a certain distance from the interior, penetrating only the lower rocks; but none can have reached the upper without penetrating the lower. That granite should be most frequently associated with the lowest rocks follows, too, from the very nature of granite. Molten rock that reached or came near to the surface would not, on consolidating, form granite, but some other kind of igneous rock—a felsite trap or a trachytic lava, as the case might be. There is also still another reason why granite is found principally in connection with low rocks that have formerly been deep-seated, and that is, that all granite now found at the surface must be there in consequence of vast denudation having taken place, by which great masses of other rocks have been removed, together perhaps with much of the granite that once existed above the present surface. This denudation of course exposes the lower rock to view, while the parts of the higher rocks that were perhaps equally penetrated by the granite have been swept off and removed (see fig. 67); the other parts which remain being now at a distance from the granite, and showing no signs of such penetration.

It is therefore where the lowest or oldest rocks come up to the surface that we should expect most frequently to meet with surface granite, as we find to be the case. There is a remarkable class of results which follow from this deep-seated origin of granite, and from the necessity of great denudation having taken place before it can appear at the surface.

In the first place, it proves the fact of this denudation having occurred. Wherever we find granite forming the surface of the ground, however lofty may be the summits of the granite mountains, or however widely spread the extent of the granite plains, we may feel sure that at the time of its consolidation it was covered with a thickness of at least several thousand feet of other rock, and that this thickness has been removed by the gradual action of erosion by moving water.

2dly. We may in many cases ascertain the date of this denudation, namely, that it took place and was completed before such and such a geological period; and thus we get a geological date for the production of the present outline of the surface of the ground.

3dly. We get a date for the formation or consolidation of the granite itself, since we know that this must have occurred previously to the denudation.

In the case, for instance, of the granites of the west of England and the S.E. of Ireland, mentioned before, we are able to prove that the granite of Wicklow, &c., is older than the granite of Cornwall. We saw, indeed, that the Wicklow granite penetrated older rocks than did that of Cornwall; but, so far, there was nothing to tell us when the Wicklow granite penetrated those rocks. It might have been that the granites were produced at the same time, that of Wicklow only reaching so far as the Silurian rocks, while that of Cornwall burst through into the rock above, namely, the Devonian and Carboniferous.

If, however, we follow the Wicklow granite into the adjacent counties of Carlow and Kilkenny, we should find that rocks of nearly the same age as those of Devon and Cornwall, namely, those called Old red sandstone and Carboniferous limestone, reposed directly upon the granite in such a way as to show that not only had the granite been cooled and consolidated, but that it had been denuded and brought to the surface in that locality before the Old red sandstone had commenced to be deposited.

For a space of about 25 miles, the Old red sandstone first, and then the Carboniferous limestone, overlap the Silurian, and come across it on to the granite. They are quite unaltered by the granite. The granite sends no veins into them, and moreover the lower rock, namely, the Old red sandstone, is more or less made up of sand derived from the materials of the granite, as in fig. 68, when the sandstone is partly, or entirely made up of the debris of the granite g. It is clear, then, that the bare granite formed the bottom of the sea in which those rocks were deposited; in other words, that all the vast mass of Silurian rock which had covered the granite at the time of its consolidation had been removed by denudation before the period in which the lowest of those newer rocks came into existence.

But the granite of Cornwall and Devon penetrates rocks which were deposited at the same time, or nearly so, with the Old red sandstone and Carboniferous limestone of Carlow and Kilkenny, and is therefore newer than those rocks, and consequently much newer than the Wicklow granite. But we may draw this yet further conclusion. The surface upon which the Old red sandstone of Kilkenny reposes is of course older than that rock; but that surface is continuous, with only slight modifications, over all the adjacent granitic and Silurian district of Wexford and Wicklow. The conditions as to denudation and form, &c., of the surface covered by the Old red sandstone and Carboniferous rocks, are obviously, by inspection of the map, nearly the very same conditions as those of the adjoining surface, which is uncovered by those rocks. Moreover, there is reason to believe that those rocks did once extend over much more of that surface than they do now, because detached patches of them are found here and there resting upon it. Therefore it follows that the main outlines, and all the principal features of the surface of the ground which now forms the counties of Wexford and Wicklow, and parts of the adjacent counties, are older than the period of the Old red sandstone. The principal part of the denudation by which that surface was formed took place before the period of the Old red sandstone, and any subsequent action, either atmospheric, when it was dry land, or marine, when it may have been passing through the surface of the sea, has been principally efficacious in removing rocks subsequently deposited upon it, or in modifying features, the outlines of which were graven at that ancient date.

These views on the nature and origin of granite are not exactly those which the student will find expressed in most geological works, though they are implied in the recent writings of many geologists. They are based upon what may now fairly be called the Lyellian philosophy of geology, a philosophy daily becoming more prevalent as its truth becomes more apparent and its applications more extended. The student, however, must expect still to meet with difficulties arising from the use of the old nomenclature, which is apt to still adhere to our tongues after the corresponding ideas have passed away from our thoughts.

V.—GRANITE VEINS.

Granite veins often differ sensibly in lithological character from the parent mass which they proceed from; and sometimes the external margin of the granite differs also from its deeper and more central portions. Veins very frequently become more fine-grained, and they lose commonly the mica and sometimes more or less of the quartz which the mass contains, becoming less crystalline and more earthy. Sometimes they take up into their constitution additional materials, derived from the rock which they penetrate and traverse (fig. 69). A striking instance of this latter occurrence is described by Professor Haughton in his paper in the Journal of the Geological Society, London, vol. xii., p. 3, where he describes the granite of Carlingford.

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1 This conclusion is one admitting of a much wider application than has yet been given to it. The present surface of the ground in most of the areas which are occupied by old rocks are surfaces of very ancient date, recent denudation having had but comparatively slight effect upon them. beds of the carboniferous limestone, and having its feldspar changed from an orthoclase, which was the feldspar of the granitic mass, into anorthite, in consequence of the addition of the lime which it had taken up from the limestone. Anorthite is said by the continental geologists never to occur except in recent volcanic rocks, and they appear to look upon its production as a mark of age, and suppose it, therefore, to be an impossible constituent of granite. This case, however, proves that it is a mark not of age, but of place, and of peculiarity of condition, and that a molten mass proceeding from actual granite may, in different parts of its course, contain different minerals, and become changed into different rocks according to the circumstances in which it is placed.

Other veins are to be found in granite itself, different in character from the surrounding rock, such as veins of eurite (see ante, p. 79), traversing coarsely crystalline and highly micaceous granite. Such veins may sometimes be due to subsequent intrusion of molten matter into the cracks of the granite; and when they do not consist of granitic rock, but of traps, such as greenstone and basalt, they undoubtedly are so due. In many instances, however, we believe them to be contemporaneous veins, either segregated from the mass while it was quite fluid, or perhaps more frequently, on the first commencement of consolidation, portions of the still molten mass below were injected into the cracks and fissures formed on the first attempt at consolidation of its upper portion. This we believe to be the generally true explanation of veins of eurite or other granitic matter differing from the mass of the granite. Such veins are commonly found to be confined entirely to the granite, and not to penetrate into the surrounding rocks, even when the granite itself does send off many veins into those rocks. In other cases, however, veins of "eurite," or of granite differing in texture from the surrounding granite, are seen to pass from the granite into the adjacent slates. These are of course formed subsequently to the consolidation of the granite which they traverse, but still they may in many instances be not long subsequent to that consolidation, and their consolidation may have been contemporaneous with that of lower portions of the granite.

The elvans or veins of quartziferous porphyry,—that is, a granular crystalline mixture of feldspar and quartz, which are common both in Cornwall and Devon, and near the granite of the S.E. of Ireland, are probably in reality granite veins, or veins proceeding from a granitic mass. Large masses of similar rock, however, occur in Wicklow and Wexford, forming mountainous hills with all the character of granite hills, except that the rock differs somewhat in texture from granite, and contains no mica. These rocks, for which we have suggested the name of elvanite, but which continental geologists might possibly call pegmatite, are probably one of the intermediate varieties between true granite and a purely feldspathic or feldspatho-siliceous trap (felstone). They should, however, still be retained among the granitic rocks. The other granitic rocks described in Part I. resemble granite in their mode of occurrence, being generally massive and underlying. Pegmatite, protogine, and syenite are indeed commonly mere local varieties of granite. Large masses of greenstone-porphyry, or felstone-porphyry, or quartziferous-porphyry (elvanite), also occur in some districts as massive, deep-seated, underlying rocks, with all the petrological character of granite. These rocks, however, are by no means universally found as underlying rocks, since all kinds of porphyry often occur in bed-like masses, either as great intrusive veins or dykes, more or less nearly horizontal, or as contemporaneous traps.

VI.—FORM AND POSITION OF TRAP ROCKS.

The Trapporean rocks may be especially characterized as being intrusive and overlying rocks when compared with the granitic class; but, inasmuch as they always proceed from below, it is obvious that every "overlying" mass of igneous rock must have a connection with some underlying mass by means of an intrusive pipe, dyke, or vein (see fig. 70). The terms "pipe" and "vein" sufficiently explain themselves. "Dyke" is a North British term for a "wall;" it is sometimes by miners applied to a mere fault, or fissure, but by geologists is always understood to mean a wall-like mass of igneous rock filling up a fissure in other rocks. A dyke may come up through any kind of previously existing rock, whether igneous or aqueous, trap dykes sometimes traversing granite, and overlying masses of trap resting on that or any other kind of rock whatever.

They may also reach and flow along all kinds of places—the surface of the dry land, when they become volcanic rocks, and would be called lava; the bottom of the sea, when they would probably be called lava or trap, according to its depth and the circumstances of time and pressure under which they cooled; and in between the beds of aqueous rocks at different depths, or perhaps between the horizontal or other joints of previously cooled igneous rocks, whether granitic or trapplean.

Those portions of trap rocks which have spread out upon the bottom of the sea, and have thus become buried between two consecutive deposits of aqueous matter, are called "contemporaneous traps."

In the old Silurian districts of the British islands great sheets of felstone and of feldspathic ash are thus interstratified with the aqueous rocks, and have since suffered with them all the accidents of flexure, contortion, and fracture that subsequent disturbing forces have brought upon those districts. Some fine-grained traps and ashes have undoubtedly been even affected by slaty cleavage and made into traplean slate, though as some of them, like the clinkstones of Mont Dor and Velay, may assume a finely laminated or slaty structure on cooling, this character requires to be very carefully observed before it is attributed to the same cause that cleaved the aqueous rocks.

Felstones, both contemporaneous and intrusive, occur also in great variety and in important masses in the Devonian and Carboniferous rocks of the S.W. of Ireland, near Kilnarey and near Berehaven.

Greenstones occur likewise in contemporaneous beds interstratified with both "ash" and aqueous rocks. The beds of "coalstone" in the limestone of Derbyshire form one

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1 Recent explorations in company with Professor Haughton, induce us to believe that this elvan-like rock is only the external skin, as it were, of true granite below. In other cases both felsstones and greenstones have been injected as great sheets, or as dykes, or as veins, into the previously existing rocks.

In the case of intrusive sheets of trap running in between beds of other rock, we may suppose that having been forced up through previously formed fissures to a certain height, the molten rock then met with such an opposition above that it was as easy for the expansive force which was impelling it to lift the beds above as to break through them. The planes of stratification then became those of least resistance; some horizontal cavities or some marked division between the beds was perhaps taken advantage of, and the molten stream, beginning to flow in, was injected with sufficient force to float the mass above upon its surface.

Sheets of greenstone thus injected have been traced by the government surveyors sometimes for miles among the Silurian rocks of North Wales. They have been found also by mining in the South Staffordshire coal-field over an area of above 20 square miles, with a thickness varying from 15 to 60 feet. (Records of School of Mines, vol. I., part ii., p. 244.)

VII.—DISTINCTION BETWEEN INTRUSIVE AND CONTEMPORANEOUS TRAP.

It is sometimes not very easy to distinguish between such injected sheets and beds of contemporaneous trap.

If a sheet of trap rock (whether felsstone or greenstone), after running for some distance between two certain beds, cut up or down and proceed between other beds, as in fig. 71, it is obviously intrusive and not contemporaneous.

If the beds above a sheet of trap be as much altered or "baked" by the igneous rock as those below, or if it send any veins up into the beds above it, it is equally plain that it must be an intrusive sheet.

If, however, the bed below the trap be altered, while that above it, composed of equally alterable materials, is quite unaffected, we may conclude that the trap was poured out and flowed over the surface of the lower bed, and that the upper bed was subsequently deposited upon it; in other words, that the trap is contemporaneous and not intrusive as regards the beds in that place.

This conclusion would be confirmed if the upper surface of the trap be rugged and uneven, and if the stratification and lamination of the bed above conformed to these rugosities, as suggested in fig. 72.

In the "toadstone" of Derbyshire globular masses of the upper surface are often almost completely included in the superincumbent limestone, clearly showing that the lime-

resembles a toad in colour, or more probably derived from the German word "todstein" or "dead stone," because the lead veins "die out" on approaching the toadstone, and were supposed not to reappear beneath it.

stone was deposited at the bottom of the sea on the uneven surface of the cooled trap.

If, again, the bed above the trap contained any fragments clearly derived from the erosion of the trap, it would prove the trap to be a contemporaneous one. At Carrig-o-gunnel, near Limerick, a great mass of greenstone, sometime amygdaloidal, is overlaid by a still larger mass of brecciated "ash," consisting of fragments of trap and fragments of limestone, and the beds of limestone immediately above this contain rounded pebbles and small flakes of the trap, demonstrating that it was formed by an outburst in the bed of the sea in which the adjacent limestone was being deposited.

When beds of trap (whether purely feldspathic or feldspatho-hornblende) are clearly interstratified with beds of "ash" or "tuff" of the same character, whether that ash were subaerial or submarine ash, it becomes almost certain that the trap is contemporaneous; for that ash is clearly derived from some contemporaneous trap somewhere, and the chances would be greatly against a sheet of similar trap being subsequently injected into those ashes without producing in them great and obvious alteration, or cutting them with dykes and veins so as to clearly show its intrusive character.

Even should the ash show a considerable amount of alteration from its original state as a mechanical deposit, such, for instance, as the production of crystals of feldspar, it would not be conclusive evidence against its being an "ash," or against the contemporaneous age of the trap beds associated with it, since such alteration might be the result of a subsequent general action which had taken place with regard to the whole mass of the rocks, but had produced a greater effect on the "ash" than on the other rocks, because its nature made it more easily impressible, and more open and liable to change than the solid igneous or the simple and more homogeneous aqueous rocks.

It is partly, perhaps, for this reason, as well as on account of the original alternation and partial blending of the results of aqueous deposition and igneous outflows and dejections, that in some highly and generally altered districts such as North Wales and the lake district in England, the southeast of Ireland, and the Border Highlands of Scotland, it is often difficult to determine the difference between actual trap and "ash" or between ash and other mechanically-formed rocks, such as some varieties of sandstone or slate. In such districts we get great irregular bosses and mountainous masses of trap of various kinds, apparently the centres or foci of eruption; we get huge continuous sheets of

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1 The student must regard the term "ash," introduced by Sir H. De la Beche, as merely an English synonym of the Italian word "tuff" or "tufo," when the latter is applied to igneous materials. The advantage of using the term "ash" is the avoidance of the ambiguity arising from "tufo" being sometimes applied to calcareous or other depositions of a soft friable character.

2 See the "Memoirs" of Professor Sedgwick in Proceedings of Geological Society; also his "Letters to Wordsworth" in the Guide to the Lake, and Introduction to Palaeozoic Rocks, 3d Fasciculus; also Murchison's Silurian System, and the Maps and Sections of North Wales and south-east of Ireland, published by the Geological Survey. felstone and other kinds of trap spreading over great areas interstratified with "ash," sandstone, and slate; we get still more widely-spread sheets of "ash," sometimes hardly distinguishable from trap when near the igneous foci, but becoming thinner and more obviously mechanical, more completely conglomeritic or brecciated, or more calcareous and more regularly bedded, as we proceed from these foci, and we get the whole of these rocks cut through and penetrated in different places by subsequently formed dykes, veins, and intrusive sheets of other traps (greenstones, felstones, syenites, elvanites, &c.), altering the rocks more or less entirely according either to their chemical composition or to the mass of the intrusive trap, and thus completing the complexity and confusion which the geologist has to unravel.

When such a district has been greatly upheaved and disturbed, thrown into many and complicated folds, and broken by many faults running in various directions, heaving and dislocating the rocks now one way and now another, and with ever-varying amounts, sometimes throwing them as much as three or four thousand feet from the level of the corresponding beds on the other side of the fault; when, in addition to this, such a district has been worn and eroded into all kinds of hollows, valleys, and glens, with precipitous cliffs and crags, separated by more or less inaccessible ravines; and when, yet more, the rocks are frequently disguised by partial decomposition, and concealed over wide intervening spaces by soil, by vegetation, or by superficial accumulations of gravel, clay, and sand, it will be readily understood that it is no easy or unlabourious task, though often a healthy and delightful one, to trace out all this complexity, to restore order to all this confusion, to delineate the outlines and positions of the rocks as they now are, and to reason back to their original state, and to the causes which produced them.

VIII.—RELATIONS BETWEEN FELSTONE AND GREENSTONE.

We have occasionally been struck in some of the districts just alluded to with the association of felstone and greenstone, it being rare to find any considerable mountain mass of felstone without irregular patches of crystalline greenstone disseminated about it. The irregular outline of these greenstone patches gave them the appearance of being subsequently intrusive into the felstone, but the frequent association of the two has sometimes led us to speculate on the possibility of the two rocks having been part of the same molten mass, and having settled or segregated apart from each other on the cooling of the whole. There seems no very cogent reason why we should necessarily suppose the whole molten mass to have been completely homogeneous; but granting that it was so, is it not possible that, when a deep-seated mass of trap commences to cool, a separation may take place, and one more fusible portion of it may be segregated from the rest, and thus one or more local centres might be established, into which the greater portion of the more fusible bases (silicates of lime and iron) should be concentrated? These local patches, which, on the ultimate complete refrigeration of the whole, would form greenstone, while the rest of the mass was felstone or elvanite (quartziferous porphyry) as the case may be, might retain their fluidity for a time, till, on the consolidation and consequent contraction of the other mass, they were squeezed in various directions into the cracks and fissures that would then be caused, and then cool rapidly in consequence of their greater extent of surface.

IX.—TRAP DYKES AND VEINS.

There do occur, however, quite a sufficient number of independent intrusive masses of greenstone, inclosed entirely in slate or other rock, to render these speculations unnecessary in many instances.

As a good instance of an intrusive vein of igneous rock we give the following (fig. 73), taken from Rec. Sch., Mines, vol. i., part 2, p. 242, as having been drawn carefully to scale.

The igneous rock here is a white trap springing out of the greenstone ("green rock") of the neighbourhood. Its chemical composition, as determined by Mr Henry, is—

| Substance | Percentage | |-----------------|-----------| | Silica | 38.830 | | Alumina | 13.250 | | Lime | 3.925 | | Magnesia | 4.180 | | Soda | 0.971 | | Potash | 0.422 | | Protosil of Iron| 13.830 | | Peroxide of Iron| 7.365 | | Carbonic acid | 9.320 | | Water | 11.010 |

showing a great amount of variation from any ordinary greenstone, in the presence of so large a quantity of carbonic acid. This alteration is probably the result of its having come in contact with a coal, and having been consequently affected by the subsequent percolation of carbonic acid, which has converted the silicates of lime and iron into carbonates. The alteration of the coal, in consequence of the heat of the trap, is equally great, as it has in many places lost its bright lustre, and its regular "face" has parted with much of its bituminous or inflammable character, and more nearly resembles anthracite than bituminous coal, though different from both, being often full of concretions of iron pyrites, or of carbonate of lime, or other minerals. In the language of the colliers, the coal is said to be "blackened," and to be now "brazil," or "brasil," and consequently not worth the trouble of "getting."

A wonderful example of a trap dyke is the one so well known in the north of England as the Cockfield Fell dyke, a nearly vertical wall of trap, 18 or 20 yards thick, which runs in a nearly straight line from north-west to south-east, for a distance of about 70 miles, cutting through all the rocks from the coal measures into the lower coals, and baking the lias and every other rock it meets with for a distance of some yards from its sides. Its effect on one of the coal beds under Cockfield Fell, is well described by Mr William in the Transactions of the Natural History Society of Newcastle, vol. ii., p. 343. The coal, I believe, is originally about 6 or 8 feet thick, one of the principal bituminous coals of the district. In approaching the dyke, it begins to be affected at a distance of 50 yards from it; it first loses the calcareous spar which lines the joints and faces of the coal, and begins to look dull, grows tender and short, and also loses its quality for burning. As it comes nearer it assumes the appearance of half-burnt cinder, and approaching still nearer the dyke, it grows less and less in thickness, becoming a pretty hard cinder only 2 feet 6 inches in thickness. Eight yards further it is converted into real cinder, and more immediately in contact with the dyke, it becomes by degrees a black substance, called by the miners "dawk," or "swad," resembling soot caked together, the seam being reduced to 9 inches in thickness. There is also a large portion of pyrites lodged in the roof of that part of the seam which has been reduced to cinder. Basalt is rarely, if ever, found as an underlying rock, and not often as an intrusive sheet. It occurs commonly either as a dyke, or as an overlying mass. One of the most celebrated plateaux of basalt is that in the north-east of Ireland, covering almost the whole county of Antrim with a mass 300 or 400 feet in thickness, and 50 miles long by 30 wide, or about 1200 square miles in area. The basalt occurs in three or four sheets, in many places beautifully columnar and interstratified with beds of ash or "ochre," as it is called, associated with beds of lignite; one of the columnar beds dipping gradually into the sea on the north coast is known as the Giant's Causeway. Many dykes are perceivable in the district, cutting through different kinds of rock, altering the Lias shales into a Lydian stone, and the Chalk into a crystalline marble. The basalt of the west of Scotland is likewise beautifully columnar, as at Fingall's Cave and other places, while that of Arthur's Seat is massive, and often crystalline, showing distinct crystals of olivine, and being highly magnetic from the abundance of magnetic oxide of iron.

The ash associated with the basalt of the Calton Hill is very admirably exhibited on all sides of it.

The greenstone of Salisbury Crags has greatly altered and indurated the gritstone below it (one of the Carboniferous sandstones), which is converted into a kind of quartz rock.

It is probable that all these basalts and greenstones were of submarine formation, but the lower part of many lava streams proceeding from subaerial volcanoes, or at all events from volcanoes which are now subaerial, are as regularly columnar basalt as the Giant's Causeway itself.

XI.—FORMS AND POSITIONS OF VOLCANIC ROCKS.

Lavas differ from traps partly in mineral character, such as the occurrence of augite instead of hornblende, and of labradorite or anorthite instead of orthoclase, &c., but principally in the texture and form of the rocks, rather than their composition.

True lavas have always been poured out either on the dry land or in shallow water, forming regular flows or "coulées" of molten rock. Cooled under these circumstances, the upper surface of a lava stream is generally quite porous and vesicular, from the escape of the gases pent up within. The upper portion of such a bed consists of loose blocks of cinders of all sizes, from rough masses of 2 or 3 feet in diameter, to those of as many inches. It might be likened to a mass of clinkers, slags, and cinders from a huge foundry. The far end of a lava stream has been described as a slowly-moving mass of loose porous blocks, gradually rolling and tumbling over each other with a loud rattling noise, giving evidence of the pressure of a viscous mass of cooling lava within. The upper end of a lava stream, where it issues perfectly fluid from the intense heat of the volcanic orifice, moves much more rapidly.

All rock is a bad conductor of heat, so that, when once a lava stream acquires a cooled crust, the mass within may remain glowing hot for a considerable period of time. We are told of persons walking about on the cooled surface of a lava stream while able to roast eggs or light cigars in the cracks and crevices of the crust. Caverns are sometimes formed in lava streams by the sudden escape of the molten mass below, leaving the cooled crust standing like the roof of a tunnel.

In such a mass it is obvious that, while the upper surface was light, porous, and cinery, the lower portion, cooling much more slowly, and under pressure, might be solid, compact, or crystalline. As a matter of fact, wherever old lava streams have been cut into, either naturally or artificially, and their lower portions laid open to our inspection, we find the vesicular character of the upper surface gradually disappearing below, and the rock passing quickly into a hard, compact stone, often columnar, and frequently quite crystalline.

The hornblendic or augitic lavas more readily assume the columnar form than the feldspathic lavas or trachytes, which, however, on the other hand, are often much more highly crystalline than the augitic dolerites or basalts.

The lower parts of many lava streams are not to be distinguished by any internal characters (and probably not by any differences in chemical composition) from columnar basalt.

Many old basalts, indeed, which are ordinarily considered as trappean rocks, may have had a porous cinery upper surface at the time of their formation, that surface having been subsequently washed away by denudation.

Almost all true lavas are embedded in, and surrounded by, vast piles of ashes, dust, and fragments, ejected from the volcanic orifice from which they themselves proceed, or from some neighbouring orifice. They commonly issue from a cup-like hole, or crater, either on the summit or on the flanks of a great conical pile of such loose ejectments.

XII.—ELEVATION THEORY OF CRATERS.

Von Buch and other geologists formerly took it for granted that lava would not solidify into thick masses of compact or crystalline stone, if it had been poured out down a slope having an inclination of more than 3° or 4° to the horizon. It has been shown, however, by Sir C. Lyell and others, that this assumption was a gratuitous one.

Upon it was based the "elevation theory" of cones and craters, which supposed it necessary that all lava streams, and the associated beds of ashes, &c., should have been once nearly horizontal, and subsequently elevated into their present inclined position and qua-qua-versal dip, by an upheaving force acting on a central point. This theory is here mentioned chiefly that the student may know what the elevation-crater theory was.

It is not intended to deny the possibility of such an elevation, since a dome-shaped elevation and qua-qua-versal dip is a common occurrence among stratified rocks, and may have been given equally to igneous rocks, as in the case of Mount Jornillo, stated by Humboldt to have swollen up like a bladder to a height of 1600 feet above the surrounding ground. But we wish to guard the student against supposing it the necessary mode of formation of all volcanic cones and all crateriform hollows from which beds of lava incline downwards in all directions. All, or nearly all, volcanic cones have been formed by the frequent ejection into the air of cinders, blocks, and ashes, from one central orifice, round which they have fallen nearly equally in all directions (except perhaps that from which the wind was blowing at the time), together with the occasional outflow of a molten lava stream, which has either broken down one side of the lip of the crater, or has broken through at some lower and weaker point in the flanks of the cone.

On the flanks of a great volcanic mountain minor lateral cones and craters are frequent at the surface, and are probably much more numerous within; many former excrescences having been buried and concealed by subsequent accumulations (whether of lava streams or ashes) ejected from the central region.

Professor Ramsay informs us that Professor Edward Forbes had conceived the idea, which has lately been completely confirmed by the Geological Survey, that the igneous rocks around Edinburgh belonged to two very different periods, the one part probably Carboniferous, and the other much more recent, probably Tertiary, perhaps contemporaneous with the Miocene (?) basalts of the north of Ireland and the west of England. In great volcanic mountains it is not unfrequent to find the ruins of a former grand central cone, from the interior of which a new central cone is commencing to grow. This is the case in the Peak of Teneriffe, where the present cone rises from a corner of the space now called the Pumice Plains, that was once the interior of a much grander cone, the ruined walls of which may still be traced in a line of crags surrounding the plains.

In the volcanic mountain of the Bromo in Java, which lies in the centre of a great volcanic range, from one end of which Mount Semiri rises to a height of 12,000 feet, and from the other Mount Arjuno to 11,000 feet, there is an excellent example of a similar structure. The Bromo is a flat-topped mountain, about 8000 feet high, formed by a narrow circular ridge sloping steeply down on the outside, and having a perpendicular precipice within, only broken and accessible at one or two points, and being generally 1000 feet in height. The circular space within this great wall is 4 or 5 miles in diameter, and a large part of it is a flat expanse of fine sand, called the Laut Pasir, or Sandy Sea. From near the centre of this rises a rough conical mound, 600 or 800 feet high, deeply furrowed on all sides, and having on one side a number of subordinate cones and craters, partly growing out of it, as it were. One of these had been frequently active in 1845, when we visited it, and was then belching out much smoke and steam, with a great rumbling noise proceeding from the depths of the funnel-like crater.

For further details of volcanic mountains, and an account of their distribution, we must refer the reader to Lyell's Principles of Geology, Daubeny on Volcanoes, Wilkes's Voyage, Scrope's Central France, Johnstone's Physical Atlas, Walterhausen's Etna, &c. See also a very interesting paper by Mr Scrope in the Geological Journal, vol. xii., p. 4.

Just as among the trap rocks we found dykes and veins frequent, seeming sometimes to be the mere extensions of the mass below into the cracks and crevices of the rocks above or around it, sometimes apparently the feeders of overlying masses, so we should find volcanic cones and the surrounding districts penetrated in every direction by dykes and veins of compact lava, serving often to bind together or to support the otherwise rather incoherent materials; and we should know, although we could not see it, that every lava stream had its central pipe or feeder in the interior of the mass from which it had proceeded. It is probable that, both in the case of traps and lavas, the size of the dykes or feeders often bears but a small proportion to the mass of the overlying rocks that proceeded from them.

It is not absolutely necessary, in the case of a volcanic cone, that the flow of lava and the central pipe or feeder should remain in connection, and cool and consolidate together; for when the lava ceased to be impelled so as to flow over the crater, the portion left in the funnel might sink down, and perhaps ultimately cool and consolidate at a considerable distance below, and might possibly make even a different kind of rock from the ejected mass.

This may sometimes occur also among trap rocks, since it is quite easy to conceive that an overlying mass or an injected bed might be deserted by its feeder on the internal impelling power being withdrawn, and the orifice by which it rose might be closed, so that two kinds of rock may be formed at different places, and possibly of rather different character, though once perhaps actually forming part of the same molten mass.

In many volcanic regions there appears to be an alternation, or to have been a succession, in the different products; the lavas being at one time trachyte, and at another dolerite. It was formerly supposed that the trachyte was always the lower, or the older of the two, and that flows of trachyte were never found above flows of basalt or dolerite. We are not prepared to say how far this relation of position has been borne out or not by recent researches.

Bunsen, however, in a paper formerly cited (Sc. Memoirs), in speaking of the trachytic and augitic lavas of Iceland, refers their origin to two separate volcanic foci, and even speaks of a third separate volcanic focus for the intermediate lavas, though he also speaks favourably in another place of all the volcanic rocks arising from one mass.

The identity or very great similarity of the various volcanic products in all parts of the world seems to point to a common origin for them. The frequent association in all parts of the earth of the two great classes of these products, trachytic or purely feldspathic (or highly siliceous, with little alkali, lime, or iron), and those in which the feldspathic minerals are largely mingled with hornblende or augite (containing much alkali, lime, and iron), seems to show that their separation is not so much due to diversity of origin, as to some cause tending to segregate the one from the other, out of a generally diffused mass, in which the constituents of both may be equally mingled.

The association previously mentioned of felsstone and greenstone among the traps seems to be reproduced in that of trachyte and dolerite among the lavas. In both instances the occurrence of pure or unmixed feldspathic rocks is less frequent and less universal than that of those in which the feldspar is mingled with the more basic minerals. Trachytes and feldstones seem both to be confined to certain localities, in which, however, they are very abundant, sometimes alone, and sometimes largely mingled with dolerites, basalts, or greenstones. These latter rocks, on the contrary, are not only found in association with the former, almost wherever these igneous rocks appear, but also in many other districts, in large or small quantities, unaccompanied by any other igneous rocks.

If we assume all igneous rocks to proceed either from one central molten mass of equable constitution throughout, or from separately fused portions of perfectly similar constitution, might we not suppose that the difference in the constitution of the various products which we find at the surface depended on the circumstances and conditions in which they had been placed? The portions now open to our examination had probably to pass through different thicknesses and different kinds of other rocks; they would be placed then under different conditions of temperature and pressure, which might perhaps alone cause a separation to take place in their different ingredients; they might also take up in their passage other ingredients of different character from those which they originally possessed, or larger proportions of one or other of their original ingredients. In those places, or at those times, when violent accessions of heat approached most nearly to the surface, trachytes and felsstones might be poured out, while at other periods of less intensity no molten rock could reach the surface unless it were composed of more easily fusible minerals. These more readily fusible substances might be conceived either to have separated in liquid strings and veins from the consolidating rocks below, or to have been acquired by the upper portion of the mass from the rocks it met with in its passage towards the surface, the substances thus added having acted as an additional flux to matter which would otherwise have solidified before it could have been poured out.

Some such hypothesis as this seems less forced than one which obliges us to suppose separate deep-seated foci or reservoirs for every variety of igneous rock, those varieties frequently occurring in the same district, and alternating one with the other over the same space of ground.

If it be well founded, it will enable us to account for the gradual changes in one connected igneous mass, as also for the veins and patches of different character sometimes to be found occurring very abruptly in such masses, independently of the supposition of a subsequent intrusion of one igneous rock through the body of another. This would often relieve us of a difficulty where the veins are confined to the igneous rock and do not penetrate the adjacent aqueous rocks. We might then look upon such veins as veins of segregation, occurring probably at the time of the contraction consequent upon the mass of the rock passing from a molten to a solid state, or from a pasty to a crystalline state (see ante, p. 84), while yet some parts of it remained fluid.

XVI.—ORIGIN OF VOLCANIC ACTION.

It still remains an undecided question whether the heat by which rocks are molten in the interior of the earth be due to an original central heat or to mere local causes. Dr Daubeny maintains Davy's hypothesis of the probability of volcanoes arising from the heat generated by the oxidation of large masses of the metallic bases of the earths and alkalies, independently of any central heat. We have, however, already seen that there is a high degree of probability for the existence of a great internal temperature.

Professor Phillips has remarked that the fact of internal heat by no means excludes the hypothesis of the local intensity of volcanic action near the surface being due to the local chemical causes to which Dr Daubeny ascribes them. The linear arrangement, however, of the great volcanic bands of the earth's surface suggests, as Humboldt says, the idea of their being arranged over great cracks in the crust of it, by which the molten matter of the interior escapes to the surface. The existence of these cracks, on the other hand, may be equally efficient, as allowing the access of water to the elementary or simple substances of the interior, and their consequent oxidization and combustion.

Even granting the central heat and fluidity of the earth to be a fact, there still seems to be a difficulty in supposing our lava streams to have any direct connection with this central fluid portion. If they had, they would apparently be kept constantly molten, and constantly at the same height in all volcanoes, unless, indeed, we suppose the attraction of gravitation not to be universally perpendicular to the earth's mean surface.

XVII.—THE CONTENTS OF MINERAL VEINS.

Having described the veins of igneous rock, and the cracks, fissures, and faults which affect all rocks in different places, we are now in a position to re-examine the subject of mineral veins, with a view especially to their contents.

In veins or dykes of igneous rock, we have seen that they are either veins of segregation with or without fissures, or veins of injection, liquid matter having been forced into fissures, either previously existing or formed at the time of injection. There is commonly in such veins no farther dislocation of the adjacent rocks than will allow of the intrusion of the igneous matter.

We have also seen that in "faults" the fissure will probably be closed in soft and easily compressible rocks, while in hard ones it will often stand open, either wholly or in part; the walls or sides of the fissure being kept asunder by the knobs and protuberances which result from the irregularities of its form.

It is of course quite possible that molten matter may gain access to such a fissure, and fill it up with a dyke or vein of igneous rock. If, however, it be not so filled up, it will be ultimately more or less completely filled with other kinds of mineral matter, and in a different way.

Blocks and fragments of the adjacent rocks may fall into such a fissure, and such blocks are often found in mineral veins. If it have anywhere any open communication with the surface, different matters may be swept into it by floods or springs. Branches of trees, gravel, sand, and clay, and other surface matters, have accordingly been found in mineral veins.

Besides these matters, however, thus introduced by mechanical causes, many minerals have been chemically deposited in fissures, and it is to these chemically-deposited substances that we look as the true contents of a mineral vein.

The number of minerals found in such veins is far greater than that of the minerals forming the principal constituents of rocks. Silica or quartz, however, among the earthy minerals, maintains an equally abundant presence in veins as in rocks. In addition to the earthy minerals, however, such as quartz, fluor spar, baryta, calcite, strontia, &c., mineral veins are the principal repositories of the metallic minerals, the ores of copper, lead, tin, zinc, mercury, antimony, silver, gold, platina, &c. &c.

It is to these metallic minerals that the miner of course chiefly looks, and he generally speaks of the earthy minerals as the gangue, matrix, or vein stuff of the "vein" or "lode."

The mineral contents of a vein is sometimes confusedly dispersed through it, the "vein stuff" being either crystalline or amorphous, and the ore occurring either as disseminated crystals or nests, or as "strings" or ribs. Sometimes there appears a regular arrangement of the various substances, the "cheeks" or "walls" of the "lode" being lined with a layer of crystals of one kind of substance, with their points or apices directed inwards, each of these layers being covered by a crystalline layer of another substance impressed by the crystals of the first, and therefore evidently deposited upon it, and after two or three such alternations a rib of ore is found in the centre.

In other instances the vein will be filled with only one kind of substance, sometimes the "vein stuff," sometimes the ore.

Such structures as that in fig. 74 seem necessarily to involve the idea of successive depositions of the different Assuming, however, the vein to have been filled with a liquid solution of these minerals, it is not absolutely necessary to suppose them to have been successively introduced, since all the substances may have been in solution together, and circumstances having been favourable at one time to the deposition of one substance and to that of another at another time.

In some veins it appears that after being filled up, subsequent movements have taken place, causing fresh openings, and new deposits of crystals formed in these openings. These subsequent movements have often produced shining striated surfaces, the effect of enormous friction, which are known as "slickensides;" but these are not confined to veins, since they are found in "faults," and in broken or contorted and fractured rocks of all kinds, where a grinding motion has been communicated to different parts of the rock.

Where "lodes" and "cross courses" occur together in a district, their contents are often different, one kind of minerals being found in one and another in the other. Where the date of the "cross course" is newer than that of the "lode," which is often the case, it is easy to understand the difference in their contents. When, however, the two veins are contemporaneous, as sometimes happens, it is not so easy.

Sometimes the cross courses contain no ores themselves, but the parts of the right lodes near the cross courses are found to be more than usually rich. By "right lodes" are meant those mineral veins which run parallel to each other with a certain magnetic bearing over a given district of country, and by "cross courses" those which cross these more or less nearly at right angles. Both in the north and west of England the "right lodes" run nearly east and west, the "cross courses" nearly north and south.

Of the various hypotheses proposed to account for the origin of the contents of mineral veins, none perhaps are altogether satisfactory. Mr. Were Fox called attention to the fact of currents of electricity traversing veins; and there appears no difficulty in supposing that if veins are filled with water more or less acidulated and impregnated with mineral solutions, a great natural "electro-plating" process may be set up, by which different minerals may be deposited at different times or in different parts of the walls of the lodes. Where the minerals, however, and especially the metallic ores, are derived from, is another question, whether directly from original repositories below, or indirectly by segregation in minute particles from the adjacent rocks. That the fissure should remain open for a great and indefinite period of time, and that its sides should be hard rock, seem the two essential conditions, though perhaps the latter may only be necessary to ensure the former.

The mineral contents of veins seem to be by no means permanent, even when complete, since crystals of minerals are often found that have not their true form, but the form of some other mineral; the originally deposited crystal having decomposed and been removed, and the newer one deposited in its place. Vast periods of time must have elapsed for such processes to have taken place.

If the mineral contents of veins have not been deposited from aqueous solutions either filling the veins or trickling down their sides, the only other alternative appears to be to suppose them the result of sublimation. This supposition seems to have lately lost the favour with which it was once received, it having been objected to it, that the temperature of the walls of the vein must necessarily be too low for sublimation to take place, or for minerals to continue in a state of vapour in any but the lower and more deeply-seated parts of veins. To this objection, however, it might be replied that the mineral veins, now near the surface, were probably deep-seated, and covered with vast thicknesses of other rock, at the time the minerals were formed in them, and therefore their walls may have had then a very high temperature. Moreover, it may be doubted how far it is impossible for minerals to be brought into them in a state of vapour even now. With respect to lead, at all events, we recollect to have been shown a chimney a mile long, built along the side of a hill, proceeding from some lead works in the county of Northumberland, with chambers in it at intervals, and to have been told that its expense was repaid in a few years by the quantity of lead deposited in these chambers, which would otherwise have been dissipated in the state of vapour into the atmosphere. It was the noxious action of these mineral vapours on the surrounding crops which first necessitated the erection of the chimney.

It appears then, that, provided it be possible for mineral vapours to be generated and gain access to fissures in rocks, it is not impossible for some of them at least to be condensed and deposited on the sides of lodes in the way in which we now find them, even close to the present surface.

This method of formation, however, would not account for the strings of ore that are often found leading from lodes into the minute cracks of the walls, frequently horizontal, and often more or less completely blending with the rock itself; nor would it account for the detached nests and concretionary lumps of ore frequently found, entirely inclosed in rock, both in the neighbourhood of mineral veins and elsewhere.

In the rounded concretionary blocks of ironstone, for instance, found in the clays of the coal measures, crystals of galena and of blende are often found together with those of iron pyrites, carbonate of lime, and others. In the Carboniferous limestone and Old red sandstone rocks of the south of Ireland and elsewhere, small cavities are found, not so large as the fist, filled up with crystalline concretions of galena and of specular iron ore.

Any explanation of the formation of the contents of mineral veins must include that also of the deposit of these detached and isolated nests of minerals, as well as the formation of quartz veins in general, and all other veins, and strings, and nests, and cavities that have been more or less completely filled by any crystallized mineral substances of whatever kind.

If we take the crystalline stalactites and stalagmites forming in caverns as the basis of our reasoning on this subject, and suppose all other cavities to have been either filled or to be in process of filling by crystalline minerals

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1 As this was a recollection of twenty years ago, we wrote to Mr. Sopwith, the eminent manager of Mr. Beaumont's mines, respecting it, and in answer we were informed by him that formerly "large quantities of lead were carried off in the state of vapour and deposited on the surrounding land, where vegetation was destroyed, and the health of both men and animals seriously affected. This led to the construction of the horizontal and slightly inclined galleries in use at Mr. Beaumont's mines, and the quantity of lead extracted rapidly repaid the cost of construction. The latest addition of this kind was made at Allen Mill, and it completed a length of 8789 yards (nearly five miles) of stone gallery (or chimney) from that mill alone. This gallery is eight feet high and six feet wide, and is in two divisions widely separated, one being in use during such times as the fusee or deposit (a black oxide of lead) is taken out of the other. There are also upwards of four miles of gallery for the same purpose connected with other mills belonging to Mr. Beaumont in the same district and in Durham, and further extensions are contemplated. The value of the lead thus saved from being totally dissipated and dispersed, and obtained from what might be called chimney scrapings, considerably exceeds ten thousand pounds sterling annually. It should be observed, however, that the mines of which these chimneys or flues are an appendage, are the largest lead mines in the world, and that the royalties or freehold rights of mining belonging to Mr. Beaumont, in the county of Northumberland alone, extend over more than a hundred square miles, in addition to extensive leasehold mines in the county of Durham." Geology. in a similar way, we shall probably not be far from the truth.

We may not be so well acquainted with the exact nature of the process by which other minerals are dissolved in one place and redeposited in another, as we are in the case of carbonate of lime; but we may feel pretty well assured that water is the principal medium through which other agents act in the one case, as carbonic acid does in the other.

The association of different minerals in different veins may possibly some day throw some light on the nature of these processes. Werner, for instance, says that galena or lead glance, copper pyrites, blendé, and calamine, frequently occur together; as also cobalt, copper, nickel, and native bismuth; tin, wolfram, tungsten, molybdena, and arsenical pyrites, &c. It appears that magnetic iron (the emery of the gold diggers) generally occurs with gold. Silver also is commonly found in lead ore. Recent experiments of Dr Percy show that minute quantities of gold occur in almost all lead ores, as well as in all copper and iron pyrites.

The relation between the contents of mineral veins and the nature of the rock which they traverse is also important.

The lead veins of the north of England traverse limestones, sandstones, and shales, and their contents vary according to the nature of the substances which form the walls of different parts of the "lodes." It is even said that the "lodes" vary in contents in different beds of limestone, but it does not appear that the richness of a lode is constant for any beds of limestone. When one or both walls consist of shale, the lode is always poorest, but this may be the result simply of the greater contraction of the fissure and more unstable condition of its walls when soft than when they are hard.

The supposed relation between mineral veins and the age of the rocks they traverse is probably an accidental one only. Mineral veins may be expected in all highly-indurated and greatly-fractured rocks, whatever may be their geological date. Neither does the connection between mineral veins and the occurrence of igneous rocks appear to be better founded, than on the probability that igneous rocks will be most likely to be found in the same indurated and fractured districts which we have seen to be essential for the production of mineral veins.

PART II.—PALÆONTOLOGY.

(The treatment of this part of the subject is deferred to a separate article under that head.)

PART III.—HISTORY OF THE FORMATION OF THE SERIES OF STRATIFIED ROCKS.

CHAPTER I.

PRELIMINARY OBSERVATIONS.

We have hitherto been dealing with general principles, examining structures which are common to all rocks, and referring the production of those structures to their several causes. We have had occasion to remark frequently on the vast lapse of time required for the formation of these rocks, and it remains now to classify and arrange the results of the operations that have been taking place during this vast lapse of time, and to give, as far as possible, a connected history of the events which have been concerned in the production of that external portion or crust of the earth which alone is open to our examination.

The way in which this order is to be discovered will, I think, be sufficiently obvious from what has been said before. In a former chapter we saw, that after having acquired a knowledge of the number and nature of a series of beds, by examining a cliff on a sea-shore, or other "section" where they were well exhibited, any little natural or artificial excavation in the interior of the country which enabled us to identify one of these beds assured us of the presence of all the rest above and below it. By searching out places where such "sections" were to be seen, and then following them by different indications across countries, and joining them on one to another, verifying them now and again by the discovery of other sections where they were again to be seen in more or less detail, and performing the same process for the sets of beds that successively cover them, we eventually survey great tracts of country, and arrive at a knowledge of the order and succession of subterranean groups of rock, to a much greater depth under certain localities than it would be possible to reach to by any process of mining or direct excavation.

The history of the formation of the whole crust of the globe, then, is to be learned by piecing together our knowledge of different parts of it, as they rise to the surface one from under the other, over different tracts of ground.

We might give this history in either of two ways, namely, by investigating or tracing it backwards from the present to the past, or by narrating it as nearly as possible in the order in which it occurred. We prefer the last method as the shorter and more intelligible, since it is hoped that the previous parts of this article will have sufficiently prepared the student to understand it.

As, however, to narrate this history in full, even so far as it is already known, would require a library rather than a book, what will be here given must be taken as a mere abstract,—a chronological table rather than a history,—by means of which the student will be able to refer to its proper period any more detailed account, which he may either read or observe for himself, of its different portions.

Even this abstract is a very imperfect, broken, and fragmentary one. Comparatively few parts of the earth's surface have as yet had their structure even sketched out; still fewer have been accurately surveyed, and had their details thoroughly unravelled, and placed in their proper and regular order. Many of the events, therefore, which are now supposed to have occurred contemporaneously in different places may in reality have occurred in succession; many which are supposed to have directly succeeded each other may have been separated in reality by great spaces of time, of which there are no records as yet discovered, or of which none may ever be found. It is obvious that all future discoveries may add to the time we know to have elapsed, but cannot diminish it.

As the structure of the British Islands is better known than that of any other part of the globe of equal dimensions, and contains a more complete series of rocks in a small space than any other district, we shall take that as our principal authority, as it were, for our history, pointing out the several groups of rock which were produced in this part of the globe during the several periods, and then give some of Geology, those other well-known typical groups of rock which are generally adopted, signifying the periods of ancient, middle, and modern life. Geological time, then, may be thus arranged:

3. Tertiary or Cainozoic Epoch. a. Human, Historical, or Recent period. b. Pleistocene period. c. Pliocene period. d. Miocene period. e. Eocene period.

2. Secondary or Mesozoic Epoch. f. Cretaceous period. g. Jurassic period. h. Oolite period. i. Triassic period.

1. Primary or Palaeozoic Epoch. j. Permian period. k. Carboniferous period. l. Devonian period. m. Upper (or True) Silurian period. n. Lower (or Cambro-) Silurian period. o. Cambrian period.

It will be advisable, perhaps, to say a few preliminary words as to the commencements of each of these great epochs.

The commencement of the Primary epoch has been already spoken of; and it was shown that by the very nature of the case this must be lost in the dark uncertainty of the remote past, with no clear and definite starting-point to be determined. The earliest formations of all must necessarily have been all long ago destroyed by the erosive action of water, or re-absorbed by the melting agency of internal heat; and even of those later, but still very early rocks, some of which do yet remain in a recognisable state, most of the contemporaries must have been destroyed or so metamorphosed as to be no longer recognisable. The commencement, then, of the Primary epoch must necessarily be uncertain, doubtful, and irregular.

The commencement of the Secondary epoch is a marked one, depending on a great change having taken place in the character of animal and vegetable life in the interval between the formation of the last of the Primary or Palaeozoic rocks, and the first of the Secondary ones. This change was coincident with the occurrence of great disturbances and great denudations in the parts of the world now occupied by Europe, and perhaps some other parts. It is probable, however, that the greater break, both in the position of the rocks and the character of the fossils, here than elsewhere in the series, is more apparent than real, and is owing to a great chasm in our documents, and the absence of a vast number of beds which may yet be discovered in other parts of the earth. However that may be, there is a decided line to be drawn between Primary and Secondary rocks and fossils.

The commencement of the Tertiary epoch is more arbitrary, though it is marked also by a decided change in the

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1 We may dismiss all reference to the derivation of the terms just as readily here as in many other cases. When using the term "sycophant," we rarely think of a "false fig merchant;" nor do the words "bishop" and "overseer" convey to us the same ideas, although really identical in meaning.

This was written while we had but a very faint knowledge of the nature of the St Cassian beds. The publication of Sir C. Lyell's Supplement makes English readers acquainted with the existence in the Austrian Alps of a large mass of beds of the very character here anticipated, namely, the St Cassian or Hallstatt beds, and others associated with them, having fossils of an intermediate character between those found in palaeozoic and those in mesozoic rocks. rocks and fossils, and a probable absence of a number of beds. The most marked character of the Tertiary rocks is derived from the fact that a few of the animals which came into existence at the commencement of the Tertiary epoch are still living on the globe. It would follow, then, that if these few species were now to die out and become extinct, the boundary between Secondary and Tertiary rocks would have to be shifted, or else it would be left with a still more arbitrary character than now. There is no essential difference between Secondary and Tertiary fossils. The genera are mostly the same, though the species are all different, and often not very widely different. It was for this reason that the late Professor Edward Forbes proposed to do away with the distinction between them, and to group the whole of the great series of stratified rocks, or, in other words, to divide the whole lapse of past geologic time into two great epochs only, namely, Palaeozoic and Neozoic.

In drawing up the following summary, it will be best to give under each period a brief description of the groups of rocks that may be taken as typical of those formed during the period in different parts of the earth, with their maximum thickness, as the measure of the time elapsed, and the possible importance of the group.

Reference will be made chiefly to the Celtic province, or British area, in these statements.

PRIMARY OR PALEOZOIC EPOCH.

CAMBRIAN PERIOD.

(Lower Cambrian of Professor Sedgwick.)

Typical Rocks.—Wales.—A great series of gritstones, sandstones, and slates, generally of purple and green colours, the sandstones sometimes becoming conglomeratic, and containing fragments of still older slates and grits. In the Longmynd (Salop) there is an apparent thickness of 26,000 feet of these rocks; but this enormous thickness may perhaps be due to concealed folds or reduplication of the beds. In Anglesea these rocks are largely metamorphosed into chloritic and micaceous schists and gneiss, the metamorphism having apparently taken place at a very early period.

Ireland.—A great series of grits and slates, generally of purple and green, or brown and liver-coloured hues, often interstratified with large beds of yellowish quartz rock, which are most abundant in what appears to be the upper portion of the group. In this upper portion the fossils also are found.

Cumberland.—The Skiddaw slate of Professor Sedgwick is probably of nearly the same age as the rocks above mentioned.

None of the Cambrian rocks of Wicklow and Wexford are known to be metamorphosed, though it is possible that much of the mica schist and gneiss, with altered limestone of the north of Ireland, and of Scotland, and other parts of the world, are the metamorphosed clays, sands, and limestones of this period.

Bohemia.—Probably stage A (crystalline schist) and stage B (slate and conglomerate) of M. Barrande. No fossils known.

Scandinavia.—Regio I. Fucoidarum of M. Angelia almost certainly is of this period.

America.—Sir W. Logan described rocks, apparently of this period, below the Potsdam sandstone in Canada. No fossils.

Much of the metamorphic series of America,—as of Europe the great masses of gneiss and mica schist,—are doubtless altered Cambrian, or else still more ancient rocks, the unaltered members of which may never be known to us.1

LOWER OR CAMBRO-SILURIAN PERIOD.

(Upper Cambrian of Professor Sedgwick.)

Typical Groups of Rock.—Wales and the Border Counties.

| Group | Thickness | |--------------------------------|-----------| | Lingula flags | 5000 ft | | Llandeilo flags | 5000 ft | | Caradoc Sandstone and Bala beds | 9000 | | Lower Llandovery beds | 1000 |

1. The Lingula flags.—Dark brown and blue flags and slates, interstratified in their lower beds with sandstones, and seeming to pass down by insensible gradations into the gritstones and slates of the Cambrian rocks below, to which they are quite conformable. Thickness several thousand feet.

2. Llandeilo flags.—Brown, fine-grained, rather sandy flags, and black earthy rotten slates. Thick beds of contemporaneous traps and ashes in some places. Thickness several thousand feet independent of the traps.

3. Caradoc Sandstone and Bala beds.—In Shropshire these are chiefly thick brown and yellow sandstones, often calcareous. In Merioneth, &c., they are gray grits and sandy slates, sometimes black slates with beds of sandstone. Near Bala they have a band of concretionary limestone 20 or 30 feet thick about their middle portion, called the Bala Limestone, and another smaller occasional band near the top called the Hirnant Limestone. Great masses of contemporaneous traps and ashes are interstratified with the slates and grits in some places. Thickness, without trap, about 9000 feet.

4. Lower Llandovery beds.—Gray and brown grits and conglomerates, with dark shales. Thickness several thou-

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1 Although few traces of life have hitherto been found in the Cambrian rocks, and no unaltered rocks below them are at present known, yet the conclusion that life now first began upon the globe is one that is anything but satisfactory to our mind. Even on the supposition that no more fossils should ever be found in Cambrian or still earlier rocks, the possibility of the existence of full assemblages of animal life before the Cambrian, if given a reasonable scale action spread a few stages higher than it has in the Silurian and Devonian rocks of Europe and America, and other parts of the globe, been affected by it, so as to have their organic remains obliterated and become generally converted into crystalline schists, it would have been argued that the carboniferous period was that in which life commenced upon the globe; and had large parts of the south-west of Ireland and South Wales been left unaffected by metamorphism, great formations of sandstones and slates of Devonian age, many thousand feet in thickness, might have appeared as utterly destitute of a single trace of organic existence, and therefore a proof that, during their deposition, life did not exist upon the globe. In Ireland, as in Wales, calcareous bands (coralstones, &c.) might be shown without a trace of a fossil for miles and miles, and ranging through a thickness of 10,000 or 12,000 feet of rock at the least. The present known districts where unaltered Cambrian rocks are visible may be just the parallels of such a case; and their metamorphosed contemporaries and still earlier formations, which must have been crowded with similar forms, none of which we shall ever see. We do not say that it was so, but merely that we have not yet arrived at any proof that it was not, nor has the accumulation of negative evidence been yet of any thing like sufficient extent to preclude even its probability.

2 Sir C. Lyell, in his Manual, draws the boundary between Cambrian and Silurian at the top of the Lingula flags, and palaeontologically, such a boundary seems well founded. It is, however, impossible to draw any physical boundary in North Wales between 1 and 2, since they are both similar dark-coloured slates and flags, and there is conformity of position throughout. Ireland.—The Lingula Flags are not yet known in Ireland. Their discovery would be of interest, as it would be of importance to know whether they would be conformable to the Cambrian or to the Lower Silurian rocks, or would, as in Wales, introduce conformity throughout the series.

The Lower or Cambro-Silurian rocks of Wicklow, Wexford, and Waterford, are of the Bala and Caradoc sandstone age, as shown by their fossils, with unfossiliferous beds below them that may or may not belong to the Llandeilo flags. They consist of dark blue or black and gray flags, slates and grits, sometimes, as in Wales, becoming purple, green, olive, &c. They contain many contemporaneous beds of trap and ash (feldstone, &c.) like those of Wales, and one or two calcareous bands (very like the Bala limestone), near Courtown, and at Tramore. Their thickness must be many thousand feet, but there are no good continuous sections sufficient to determine it exactly.

They repose on the Cambrian rocks below, quite unconformably, stretching directly across the ends of the beds, and coming into contact with different portions of the lower rocks.

The fossils are found only in the upper part of the series in the neighbourhood of the traps and calcareous bands, and the exact relations of the lower beds are accordingly unknown.

Another great tract of apparently similar beds stretches from the centre of Ireland (Cavan, &c.) to the coast of Down. It contains a bed of anthracite, which is worked and locally used for coal, and this is said to reappear in one or two spots in Tipperary, &c.

On the flanks of the Dublin and Wicklow granites the Lower Silurian slates and grits are greatly metamorphosed into mica and other schists, and occasionally into gneiss, full of crystals of andalusite, staurolite, schorl, feldspar, and other minerals.

Other metamorphic tracts in the north of Ireland may be also composed of metamorphosed Lower Silurian rocks.

Cumberland.—The Coniston group of Professor Sedgwick is doubtless the equivalent of the Caradoc sandstone and Bala group. Whether the group below (his chloritic slate and porphyry) ought to be placed with the Llandeilo flag or the Lingula flag, is difficult to decide in the absence of fossil evidence. The latter is perhaps the more likely of the two, and seems to be the belief of Professor Sedgwick himself.

Scotland.—The rocks of the border Highlands from Dumfries to the Lammermuir Hills belong to this period, probably both to the Llandeilo flags and the Caradoc sandstone.

Bohemia.—Stage C, argillaceous schist, and stage D, quartzites, &c., of Barrande, are of this period. Stage C probably corresponds to the Lingula flags, but is more fossiliferous, containing twenty-seven species of trilobites alone. Stage D will then answer either to the Llandeilo flags or the Caradoc sandstones, or both.

Scandinavia.—M. Angelin's Regio A, Olenorium, and Regio B, Conocorypharium, consisting of aluminous schists and limestone, approximately = stage C of Barrande, and therefore approximately = Lingula flags.

Angelini's Regions.—BC, Ceratopygarum (aluminous schist and black limestone); C, Asphorium (gray and reddish impure limestones); and D, Trimucelorum (marly schists with calcareous concretions) are together approximately = stage D of Barrande.

1 The eruption of igneous rocks at the bottom of the sea, though doubtless occasionally destructive of animal life at the moment, seems generally favourable to its development during the period. Contemporaneous trap rocks have often highly fossiliferous beds intimately associated with them.

North America.—According to Professor H. D. Rogers, Geology, the following is the series of the Lower Silurian rocks of North America:

| Group | Beds | Feet | |----------------|-------------------------------------------|------| | Hudson Group | 11. Lorraine shale and sandstones | 2000 | | | 10. Utica slate | 500 | | | 9. Trenton limestone | | | Black River Group | 8. Black River limestone | 2500 | | | 7. Bird's-eye limestone | | | Potsdam Group | 6. Chazy limestone | 100 | | | 5. Calciferous sandstone | | | | 4. Upper Primal slate | 700 | | | 3. Potsdam sandstone | 700 | | | 2. Lower Primal slate | 1200 | | | 1. Conglomerate, with quartzose, feldspar, and silty pebbles | 150 |

The beds described by Mr Dale Owen are an extension and development of the Potsdam sandstone, in the country west of Lake Michigan. They are probably of the age of the Lingula flags, or may be still older.

At the close of this period, or immediately after it, very considerable movements of elevation and disturbance took place over the area now occupied by the British Islands, and some parts of Western Europe. Denudation consequently occurred, removing large portions of the upper rocks, and exposing the surfaces of those below. The rocks of the next period, therefore, are very frequently unconformable to those of this and the preceding period, resting now on one and now on another portion of them. This unconformity always involves the supposition of a vast lapse of time to allow of the slow action of elevating and denuding forces to produce the effect. Wherever unconformity is noted in future, the student will be careful to apply these remarks.

UPPER SILURIAN PERIOD.

Typical Groups of Rocks.—England.—Siluria; the Border Counties of England and Wales:

| Group | Beds | Feet | |----------------|-------------------------------------------|------| | Ludlow Group | 10. Tilestone | 600 | | | 9. Upper Ludlow rock | 650 | | | 8. Aymestrey limestone | 100 | | | 7. Lower Ludlow rock | 1000 | | Wenlock Group | 6. Wenlock limestone | 300 | | | 5. Wenlock shale | 1500 | | | 4. Woolhope limestone | 50 | | | 3. Denbighshire sandstone | 2000 | | May Hill Group | 2. Taranon shales | 1000 | | | 1. Upper Pentamerus beds, or May Hill sandstone, or Upper Llandovery beds | 1000 |

The sandstones of the May-Hill group were at one time confounded by the geological survey with the true Caradoc sandstone, which they often greatly resemble in lithological character. Professor Sedgwick first pointed out their difference; and the officers of the Geological Survey afterwards traced the boundary between the two, and showed that the sandstones of the Upper Silurian period rested unconformably on those of the Lower. The first mistake unfortunately had a bad influence on the survey of North Wales, where a thick sandstone formation, lithologically resembling the true Caradoc formation of Shropshire, was taken for it, and therefore the Bala beds were presumed to be below the Caradoc, while in reality they were themselves its true representative. (Ramsey MS.) This thick sandstone formation of North Wales, then, described first by Mr Bowman (British Association), and then by Professor Sedgwick, under the name of Denbighshire grits, together with the other beds associated with it, requires to be admitted as a new, and, locally, a very important member of the Upper Silurian series. It has other beds underneath, more or less intimately associated with it; and the group forms the true base of the Upper Silurian series, reposing almost invariably, in an unconformable position; on the perfectly distinct Lower or Cambro-Silurian rocks below. (See Professor Ramsay's forthcoming Memoir on North Wales.)

1. Upper Llandovery sandstone, or Pentamerus beds, or May-Hill sandstone.—Gray and brown sandstones and conglomerates, with (in Shropshire) very calcareous bands, almost limestones. Thickness, 800 to 1000 feet.

2. Tarannon shales.—Generally pale gray, nearly white shales or slates, very fine grained (spoken of by Professor Sedgwick as "paste rock"), sometimes becoming of a bright-red colour. Thickness, 500 or 800 feet.

3. Denbighshire sandstones and flags.—Generally thick-bedded yellowish or brownish sandstone, largely made up of angular grains of white feldspar, with grains of quartz occasionally as large as peas, and passing into conglomerate. These are interstratified with beds of brown slaty shale, and occasionally dark, nearly black slate, overlaid by hard brown and blue flags. Thickness at least 2000 feet.

4. Woolhope limestone.—A locally occurring group of beds of gray, argillaceous, nodular, concretionary limestone, interstratified with gray shales, occasionally attaining a thickness of 100 feet.

5. Wenlock shale.—Generally dark-gray, sometimes black shale, with occasional calcareous concretions, capped by

6. Wenlock limestone.—An irregularly-occurring set of concretionary limestones, sometimes thin and flaggy, sometimes massive, highly crystalline bosses of carbonate of lime; sometimes in one, sometimes in two or three sets of beds, with interstratified shales, forming a thickness of 100 to 300 feet.

7. Lower Ludlow rock of Shropshire is generally a brown or gray sandy flag, or argillaceous sandstone, locally called mudstone.

8. Aymestrey limestone.—A nodular concretionary limestone, sometimes pure and crystalline, at others argillaceous and impure; like the Wenlock, but more local in its occurrence.

9. Upper Ludlow of Shropshire, &c.—A gray argillaceous sandstone, often calcareous, and containing calcareous nodules passing up into shales with sandstones, which gradually acquire a red colour.

10. Tilestone.—Red, shaly, and flaggy sandstones. At the base, near the junction of the Ludlow and tilestone beds, are one or two little thin but very widely extended bands, called "bone beds," full of the teeth and bones of small fish. Wherever these widely-extended but very thin beds full of peculiar fossils (the inhabitants generally of a clear sea) are met with, it may be expected that there is a great gap in the series, and that many intermediate beds, perhaps a formation or so, will be found elsewhere.

Cumberland, &c.—According to Professor Sedgwick, the following are the typical groups of rocks deposited during the Upper Silurian period in the north of England:

3. Kendal group = Ludlow rocks. 2. Ireleth slates = Wenlock rocks. 1. Coniston grits = May-Hill sandstones.

1. The Coniston grits have few fossils, and their identity with the May-Hill sandstone is therefore doubtful, although very probable.

2. The Ireleth slate group is divided into four stages: a. Lower Ireleth slate; b. Ireleth limestone; c. Upper Ireleth slate; d. Coarse slate and grit. Fossils are rare, but generally of the Wenlock type.

3. The Kendal group is divided into three stages: (a). A great group of flags and grits; fossils abundant and of the

Lower Ludlow type. (b) Thick grit and flagstone, with bands of coarse slate; fossils locally abundant, and of Upper Ludlow type. (c) Tilestones, resembling those of Shropshire, &c. (Sedgwick, Synopsis of Classification, &c.)

Scotland.—Not much has hitherto been known as to the existence of Upper Silurian rocks in Scotland. The representatives of the tilestones, however, and probably the lower groups, have lately been discovered by Mr Simon of Lesmahago, and described by Sir R. Murchison. (Geological Journal.) These are dark-gray schistose rocks, with lighter and more siliceous stony bands, and other schists containing calcareous concretions.

Ireland.—No detailed descriptions of the Upper Silurian rocks of Ireland have yet been published. The labours of Mr Griffith, however, and more recently of the Geological Survey, have shown the existence of rocks of this age on the western side of the island. The Dingle promontory contains the representatives of both the Ludlow and Wenlock rocks, and possibly of part of the May-Hill sandstone group also. Abundance of most of the characteristic fossils, and some not found in England, though occurring in the Upper Silurian rocks either of Scandinavia or of North America, have been found.

In Galway, as shown by Mr Griffith, and confirmed by Sir R. I. Murchison and others, there is a vast series of gray grits and slates reposing unconformably on mica schist, &c., and having frequently red sandstones at its base, and sometimes great beds of conglomerate in its upper part, containing perfectly-rounded pebbles and boulders of quartz rock and syenite up to 18 inches in diameter. Abundance of fossils have been found near the base of this series, comprising all the characteristic species of the May-Hill sandstone or Pentamerus beds, and in other parts an assemblage of corals like those found in the Wenlock rocks. This great group of rocks in Galway must have a thickness of several thousand feet at least, but its details have yet to be worked out.

Somewhat similar rocks form a small range of high land at Ughool, near Ballaghaderreen in Mayo, from which a great series of Wenlock corals and other Upper Silurian fossils had been collected by Mr Griffith, and also last year by Mr Kelly and ourselves.

One feels inclined to speculate from these facts on the former existence of a range of mountains rising where the Irish Sea now flows, and composed of an axis of Cambrian and Lower Silurian rocks, with Upper Silurian on their flanks sloping down into the border country of England and Wales on the one side, and to the west coast of Ireland on the other.

Bohemia.—The rocks deposited during the Upper Silurian period in what is now Bohemia are divided by M. Barrande into—Stage E, Calcaire inferieur. Stage F, Calcaire moyen. Stage G, Calcaire superieur. Stage H, Schists culminaux.

Scandinavia.—M. Angelin similarly divides the Upper Silurian rocks of this district into his Regio D, E, Harparrum—shales and white limestones; and Regio E, Cryptonomorum—limestones resting on sandstones and shales.

Of these, Stage E of Barrande and Regio E of M. Angelin certainly equal very nearly the Wenlock rocks of Sir R. Murchison, there being 18 species of Brachiopods, besides corals and other fossils common to this group of rocks in the three countries. Sir R.

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1 So long as the Denbighshire grits were supposed to be the same as the Caradoc sandstone, the unconformity of the Upper on the Lower Silurian, which in Derbyshire and Merionethshire is not very striking, was entirely overlooked.

2 In an excursion last summer with Mr John Kelly, we measured some of the smooth round boulders of syenite embedded in these Silurian rocks, and found them frequently a foot, and sometimes, though rarely, eighteen inches in diameter. Other almost equally massive conglomerates occur in the Silurian rocks of Lisbehall, south of Enniskillen. In Galway, on the northern side of the beautiful promontory of Kilbride, on the shores of Lough Mask, a magnificent assemblage of fossils is to be seen in the rocks of the beach. GEOLOGY.

Marchian cave in 1847 a list of 74 species found in the rocks of Gotland (Regio E), 47 of which occur in Britain, 13 in Ludlow rocks, and 14 in the Wenlock, the 20 others being found in both. The Regio D, E, or M. Angelini is not represented in Bohemia. It may possibly be equal to May-Hill sandstone. The stages F, G, H of Barrande are not recognisable in Scandinavia.

North America.—The rocks of this region of the age of the Upper Silurian period are—

| HELDERBERGO GROUP. | |---------------------| | 1. Upper Pentamerus limestone. | | 9. Encrinal limestone. | | 8. Delthyris shaly limestone. | | 7. Pentamerus limestone. | | 6. Tentaculite limestone. |

| ONONDAGA AND NIAGARA GROUP. | |-----------------------------| | 5. Onondaga salt group, a gray ash-coloured shale, with gypsum and rock-salt. | | 4. Niagara limestone, compact gray limestone, resting on blue calcareous shale. | | 3. Clinton group. | | c. Variegated red marls and calcareous shales. | | b. Shales and argillaceous limestone and calcareous sandstone. | | a. Greenish and yellowish slates with ferruginous sandstone. |

| CLINTON GROUP. | |----------------| | 2. Medina sandstone. | | b. White fine-grained sandstone, alternating with red and greenish shale at top. | | a. Soft brown argillaceous sandstone, and red shale. |

| MEDINA GROUP. | |---------------| | 1. Gray sandstone, with thick beds of siliceous conglomerate, containing fragments of the lower rocks. |

According to Professor Rogers (Johnston's Physical Atlas, 2d ed.), not only does the Medina group contain a conglomerate made of pebbles of the lower rocks, but the whole Upper Silurian rocks are distinctly unconformable to the Lower, as they are in Wales and other parts of the world.

DEVONIAN PERIOD.

Typical Groups of Rock.—There has long hung much obscurity over the classification of the rocks which belong to this period. This has chiefly been owing to the fact that we have in the British Islands two distinct types of rock which never come into close contiguity with each other, and do not contain any fossils in common, but are yet undoubtedly intermediate in age between the Silurian and Carboniferous periods. One of these types has long been known to British geologists as the Old Red Sandstone; the other, confined to Devon and Cornwall, was not classed with the former till Mr Lonsdale, and Professor Sedgwick, and Sir R. I. Murchison worked it out. The Old Red Sandstone type is not known on the Continent; but the rocks and fossils of Devon re-appear in the Eifel and other parts of the Continent. The Old Red Sandstone was formerly placed as the lowest rock of the Carboniferous series by some authors (Professor Phillips and others); while a part of what was formerly called Old Red Sandstone by others (Tilestone) is now placed as the upper part of the Silurian series. Recent researches by the Geological Survey in Kerry and Cork induce us to believe that what has hitherto been called Old Red Sandstone, and treated as one great group, must in reality be separated into two—the upper part, or Old Red Sandstone proper, being really the base of the Carboniferous; while the lower portion must be separated from the rest under Geology, another designation, and looked upon as more closely allied to the Silurian system. In the Dingle promontory there are good representatives of Wenlock and Ludlow rocks, the latter containing abundance of *Pentamerus Knightii* and other Ludlow fossils, surmounted quite conformably by two great groups of purple and green gritstones and conglomerates; while over all these, widely and utterly unconformable to them and to the Silurian rocks, there sweep red sandstones and conglomerates 3000 or 4000 feet thick, which pass up conformably into the base of the Carboniferous series. This upper group of red sandstones and conglomerates also contains fossils (plants in Ireland, plants and fish in Scotland) that place it in more close connection with the Carboniferous than with any formation.

We shall also separate from the rocks of this period those which are called Upper Devonian in Devonshire (the Marwood, Pilton, and Petherwin beds), and treat them as belonging to the Carboniferous period.

There remains some little doubt, perhaps, whether the middle and lower Devonian groups of Devonshire be strictly contemporaneous with the middle and lower Old Red Sandstone. The latter contain fish and a few plants only, while the former have neither fish nor plants in them—in the British Islands at all events. We shall therefore describe them separately as belonging to this period, but without attempting to draw them more closely together. In Russia, indeed, the fish of the one are found with the fossils of the other, as shown by Sir R. I. Murchison; but questions of geographical distribution arise to complicate any deductions as to exact synchronism in two such distant localities.

Devon and Cornwall.—A great series of slates, sandstones and conglomerates, and limestones, of various textures and colours, brown, blue, and red. According to Professor Sedgwick, they may be classed as follows:—

3. Dartmouth Slate Group.—Coarse roofing-slates and quartzites, ending upwards with beds of red, green, and variegated sandstone.

2. Plymouth Group. | |-------------------| | a. Coarse red sandstone and flagstone. | | b. Calcareous slates. | | c. Great Devon limestone. |

1. Liskeard or Ashburton Group.

Belgium and the Rhine.—A series of rocks of a similar type, and with similar fossils to those just mentioned, are found in this district. They are divided by M. Dumont into—

3. Eifel Group. | |----------------| | a. Eifel limestone. | | b. Gray shales, occasionally calcareous. | | c. Red sandstone and conglomerate. |

2. Aurian Group.—Bluish-gray grits, sandstones, and shales.

1. Coelentz Group.—Green and gray grits, sandstones, and shales.

Sir R. I. Murchison, in his *Siluria*, gives a slightly different classification into Lower, Middle, and Upper Devonian; the Upper containing some beds above the Eifel limestone, as follows:—

3. Upper. | |---------| | a. Clymenia and Cypridina schists. | | b. Goniatites retrocurvus schists. |

2. Middle. | |----------| | a. Eifel or Stringocephalus limestone. | | b. Wissmuthschists = Aurian group. |

1. Lower. | |--------| | a. Coblenz or Spirifer sandstone. | | b. Wissmuth schists. |

The upper division, however, is clearly the same as that which we have thought it best to transfer to the Carboniferous period.

Rocks and fossils like those of Devon and Cornwall not being known in any other part of the British Islands, we must speak of those now to be described as Devonian, with a certain reserve as to the exact propriety of the name. They have hitherto all been described as Old Red Sandstone, which has been taken as synonymous with Devonian.

Scotland.—The labours of the late lamented Hugh Mil- Geology. ler on the so-called Old Red Sandstone of Scotland have made that district classic ground. According to his classification, as given by Professor Sedgwick in his Synopsis, the series of rocks are the following:

**Upper.** 1. Yellow siliceous sandstone. 2. Impure concretionary limestone. 3. Red sandstone and conglomerate.

**Middle.** 4. Gray sandstone and earthy slate.

**Lower.** 5. Red and variegated sandstone. 6. Bituminous schists. 7. Great conglomerate and red sandstone.

The upper division we should now relegate to the base of the Carboniferous series; and Miller, in his *Testimony of the Rocks*, throws some doubt on the superposition of No. 4 above 3 and 2. It appears that they nowhere come actually into contact, and that it is possible that No. 4 may be a fresh-water deposit, more or less contemporaneous with the marine beds 3 and 2. The balance of evidence, however, both in Miller's opinion and that of Professor Sedgwick, recently confirmed to ourselves, is in favour of the order given above.

**Herefordshire and South Wales.—**The Old Red Sandstone of this large district is composed of the following groups:

| Group | Feet | |-------------------------------|---------------| | 1. Cornstone group | 6000 or 6000 | | 2. Red and yellow sandstone marls and conglomerate | 3000 or 4000 |

Of these we believe No. 1 only properly to belong to the Devonian period, and shall describe No. 2 in the Lower Carboniferous period.

1. The Cornstone group consists of a great series of red and white sandstones and red and green marls and shales, with frequent partial bands of impure concretionary limestone, locally known as "cornstone." It graduates down quite conformably and insensibly into the tilestone of the Upper Silurian period.

**Ireland: Kerry and Cork.—**In the Dingle promontory we have the following groups lying conformably on the Ludlow rocks:

| Group | Feet | |-------------------|------| | 1. Red slates and sandstones | 1000 | | 2. Glengariff grits | 6000 | | 3. Dingle beds | 4000 |

1. The red slates and sandstones lying conformably over the rocks containing *Pentamerus Knightii* and other Ludlow fossils, may possibly be the representatives of the Tilestone group; but as it contains no fossils in Kerry it is impossible to determine this satisfactorily.

2. The Glengariff grits consist of very thick-bedded massive green or purple sandstones or gritstones, of a very peculiar lithological aspect, interstratified with beds of red or green slate. Sometimes the sandstones, sometimes the slates, are calcareous, forming concretionary beds not unlike debased cornstones. Steady sections of 5000 or 6000 feet may not unfrequently be seen in these rocks in the promontories of Dingle, Iveragh (between Killarney and Valentia), and those lying between the bays of Kenmare, Bantry, Dunmanus, and Roaring Water.

3. Dingle beds.—These consist of red sandstones and slates, with beds of conglomerate, which in the Dingle promontory are thick and prominent, containing angular and subangular fragments of red jasper, horstone, felstone, and other rocks, together with pebbles of Silurian limestone or calcareous sandstone containing *Pentamerus oblongus* and other fossils of the May-Hill sandstone group.

Over the upturned and denuded edges of all these beds, as well as across the edges of the Silurian beds below, sweep the thick beds of red sandstone and conglomerate which form the Old Red Sandstone. This is the case throughout the Dingle promontory; but in that of Iveragh, on the south side of Dingle Bay, and over all the rest of the country, this unconformity is no longer perceptible, and the conglomerates also rapidly die out to the south, so that we get only the Glengariff grits covered by red and purple slates and sandstones, with no very obvious boundary between them and the Dingle beds, nor between the latter and the Old Red Sandstone.

**North America.**

| Group | Feet | |-------------------------------|------| | 9. Catskill group, red shales and red and gray sandstones, with a few white quartz pebbles | 5000 | | 8. Chemung group, gray, blue, and olive-coloured shales, and gray and brown sandstones | 3200 | | 7. Portage group, fine-grained gray flagstone, with blue shale partings | 1700 | | 6. Genesee slate, brownish-black and bluish-gray slate | 2000 | | 5. Hamilton group, brownish-gray, brownish and olive slate, with the dark-green sandstones | 600 | | 4. Maxwell shales, black and bituminous, with thin argillaceous limestones at base | 300 | | 3. Upper Helderburg or Corniferous limestones, straw-coloured, light-gray or bluish, with chert nodules | 350 | | 2. Candagalli grit, argillaceous, calcareous, thin-bedded sandstone | 300 | | 1. Oriskany sandstone, coarse yellowish calcareous sandstone | 200 |

The Oriskany sandstone is considered by its fossils to be undoubtedly contemporaneous with the Lower Devonian group of the Rhine. The others represent the superior parts of that formation, and it is possible that some of them are rather Lower Carboniferous than Devonian.

Formations possibly belonging to the Devonian period are largely developed in Australia; and characteristic fossils have been brought from China, where they are used as medicines.

The Cape of Good Hope, too, has large formations, believed to belong to the Devonian period, of which we may shortly hope to hear more from the labours of Mr Andrew Wyley.

**CARBONIFEROUS PERIOD.**

**Preliminary Observations.**—In the account of the deposits of the preceding period it will be seen that we have ventured to detach from it the rocks called Upper Old Red in Scotland and Upper Devonian in Devonshire; and by parity of reasoning, the Upper or Old Red Sandstone proper of the south of Ireland and of South Wales; and to consider the rocks so detached as forming the base of the Carboniferous system of rocks. This conclusion has been forced upon us rather unwillingly, and against our previous belief, by the examination of the structure of the south of Ireland. It has always been the opinion of the Irish geologists, especially of Mr Griffith and Mr John Kelly, of whom the latter has published this opinion in a paper in the *Journal of the Geological Society of Dublin*. The correctness of their view on this point, however, was obscured by the endeavours to identify all below the Old Red Sandstone proper with Silurian rocks, and altogether to obliterate the Devonian period. Admitting the existence of a Devonian period as intermediate between the Silurian and Carboniferous, and placing in it the rocks and fossils just described as belonging to it, we may retain the Old Red Sandstone proper, that which stretches round the Carboniferous rocks of the south-east of Ireland and those of South Wales and the border counties, and the thin skirts and patches of Old Red in North Wales and North England, and the upper part of that of Scotland, as forming the true commencement of the Carboniferous period. There is in many places a perfect blending of the Old Red into the Lower Carboniferous rocks, or into beds which contain fossils having commonly a generic and often a specific identity with undoubted Carboniferous forms. Still there are a sufficient number of peculiar species, both of plants and shells in these lower rocks, to warrant the separation of the Carboniferous sys- tem of the British Islands into an upper and a lower series, the general terms of which may be stated as follows:

**UPPER.** 1. Coal measures. 2. Carboniferous limestone. 3. Carboniferous slate, or Lower Limestone shale, with Coomhola grits and yellow sandstones.

**LOWER.** 1. Old Red Sandstone, passing up into Yellow Sandstone.

**Typical Groups of Rock.—Ireland.**—We have already said, that in the Dingle promontory there is a mass of 3000 or 4000 feet of red Sandstones and conglomerates, the true Old Red Sandstone, utterly unconformable to the Devonian and Upper Silurian rocks below, but conformable to the Carboniferous rocks above. The junction, however, of the Old Red and Carboniferous is not very well seen there, but is admirably shown when the rocks are traced round to the neighbourhood of Glengariff, at the head of Bantry Bay. In this district the Glengariff grits are the lowest rocks seen, having the characters before described, and being surmounted by a great series of purple, and red, and green sandstones and slates which must represent both the Dingle beds and the Old Red Sandstone, all lying apparently conformably, and without any marked boundary between them.

The upper part of this red series alternates with many green and gray coloured beds, and some liver-coloured slates, and in these fragments of plants are found. A little higher the red colour disappears, and we have grits and slates of various shades of green, yellow, or gray, eventually interstratified with black shales or slates. These black beds rapidly increase in thickness as we ascend, still interstratified at first with numerous sets of beds of thick massive gritstone; but above these black shales or slates alone occur, eventually becoming calcareous, and containing thin beds of impure concretionary limestone.

The fossils of these calcareous bands, which are the highest beds seen in Bantry Bay, are all Carboniferous fossils such as are found in the Lower Limestone shale of South Wales and elsewhere. Carboniferous species, shells, and encrinites, likewise occur in the shales, interstratified with the grits below, and also in the grits themselves; but there are here also other fossils which are not found in the higher part of the series. Together with these fossils are some plants similar to, but not exactly identical with, the plants usually found in the Carboniferous series, and these plants extend down into the green and gray shales interstratified with the red beds, where, however, they are not accompanied by marine species. We would group these beds, then, as follows:

| Carboniferous Slate | Feet | |--------------------|------| | Lower Limestone shale with calcareous bands | 150 | | Dark-gray and black slates and shales | 2000 | | Coomhola grit series | 2500 | | Yellow Sandstone series | 1000 | | Red Sandstone and slate | 2000 |

1. The Red or purple Sandstone and slate contains a few green or gray beds, but no fossils. It stretches continuously from the extreme west of Cork and Kerry into Waterford and Tipperary, where it reposes unconformably on the Lower Silurian rocks, having a conglomerate at its base, partly made of the fragments of the rocks it rests on, partly of well-rounded quartz pebbles. It still retains a thickness of 2000 or 3000 feet, till it dies away rapidly towards Waterford in one direction, and towards Carlow in the other, reappearing afterwards merely as little local patches here and there in the hollows of the lower rocks.

2. The Yellow Sandstone series can only be separated from No. 1 by the greater abundance of greenish, grayish, and yellowish beds among the red ones, and by the occurrence of remains of plants in the former. It is continuous with No. 1 over all the south of Ireland, and probably extends a little further than it, since the thinning out of the Old Red Sandstone seems to take place from below upwards, higher and higher beds extending further and further, showing gradual depression to have been taking place during the period.

3. The Coomhola grit series can only be separated from the yellow sandstone by the shales between the grits being dark-gray or black, and the occurrence of some marine species in some few of the beds together with the plants.

4. The dark-gray shales and slates are perfectly well marked by the absence of grit beds, but they contain few or no fossils in Bantry Bay.

5. The Lower Limestone shale cannot be separated from the shales and slates below, except by the occasional appearance of calcareous bands together with an abundance of some Carboniferous fossils. The latter rocks, Nos. 3, 4, and 5, preserve the characters and the thickness first assigned to them over all the country from Bantry Bay to the Old Head of Kinsale and the mouth of Cork Harbour, the only variation being a diminution in the number and thickness of the gritstones in the Coomhola grit series, and a corresponding increase in the dark-gray slates above. They likewise preserve their character and thickness northwards as far as Smeen on the north side of Kenmare Bay. But when we proceed to the head of this bay about Kenmare itself we find a remarkable change to have occurred. The Carboniferous limestone there makes its appearance in its ordinary form, having under it a thickness of about 50 feet of the beds first described as Lower Limestone shale, precisely similar to the shales with calcareous courses in Bantry Bay, and containing the same fossils. But at Kenmare these beds rest directly on red slates and sandstones, forming the upper part of the Old Red Sandstone; the great mass of the Carboniferous slate series, with all the Coomhola grit group that is so strongly developed 10 or 15 miles to the westward and southward, being entirely absent at Kenmare. Neither does this absence of a group of beds nearly 5000 feet thick produce any apparent unconformity, though, as all the beds are at very high angles, and a good deal contorted, it is impossible to decide whether they were originally conformable or not. North and east of Kenmare, over all the rest of the south of Ireland to Tralee, Ballybunion, and Limerick on the north, and to Cork, Youghal, and Wexford on the east, this latter type prevails, the whole of the Carboniferous slate group being absent except the small portion of it called here the Lower Limestone shale.

We believe, then, that all the beds mentioned above as lying below the Lower Limestone shale form in reality a Lower Carboniferous series, which is only locally developed in its true proportions,—introducing when it is so developed a perfect apparent continuity and blending from the base of the true Old Red Sandstone, or perhaps in some places even from the Devonian rocks themselves, up into the highest of the Carboniferous series.

**Devon and Cornwall.**—The Petherwin slates, the Pilton beds, the Marwood sandstones, and others belonging to the same period as the Carboniferous slate and Coomhola grits of Ireland.

**South Wales.**—The Old Red Sandstone surrounding the South Welsh coal-field has a base of conglomerate reposing on the Devonian cornstones, over which are red sandstones and marls, which in their upper parts have yellow sandstones interstratified with them, containing fragments of plants, and appearing to graduate upwards into the black shales and sandstones of the Lower Limestone shale, which in its upper part is interstratified with beds of limestone, passing thus into the base of the Carboniferous limestone.

**Scotland.**—In accordance with the classification here adopted, we must place in the Lower Carboniferous series the beds called Upper Old Red Sandstone of Scotland, which, if our present views be correct, should be called Old Geology. Red Sandstone only; the so-called Middle and Lower Old Red Sandstone being termed Devonian.

They consist of red sandstones and conglomerates, having in their upper part yellow sandstones, in which plants and fish remains are found, and these are believed to be connected more or less with the base of the Upper Carboniferous rocks, through the group called Calciferous sandstone by Mr Macaren, which is possibly of about the same age as the Connemara grits of the south-west of Ireland.

The Rhine.—If the views here given as to classification be correct, we must place as Lower Carboniferous the rocks called Upper Devonian in the Rhenish provinces, which are subdivided by F. Roemer into:

1. Schists with Rhynonella coeloides and Producta subaculeata. 2. Schists with many Clymenia, Goniatites, and Cypridina. 3. Limestone with Goniatites auriculae, &c. 4. Schists with Receptaculites Neptuni.

No. 1 may possibly be a Devonian rock, as the undetermined fossil called Receptaculites Neptuni occurs in Ludlow rocks at Ludlow; but the other three groups are identified with the so-called Upper Devonian of Devon, especially by the presence of the little Cypridina serratostrigata in great abundance. (Murchison, Siluria, p. 372.)

UPPER CARBONIFEROUS ROCKS.

Taking the Old Red Sandstone proper as the true base of the great Carboniferous system of Britain, and understanding that the great mass of the Carboniferous slate group above it is found only in the south-western corners of Ireland and England, dying out everywhere rapidly to the north and east, except a few of the upper beds, known as the Lower Limestone shale, which seems also to die out towards the north and east in England, though they spread over all Ireland; and taking into account that the Old Red Sandstone proper appears to be entirely wanting in Devon and Cornwall, where the Carboniferous slate rests on true Devonian rocks,—we have now to trace the range of the upper part of the Carboniferous system through the British Islands. In doing this we will again commence with the south-west portions of—

Ireland—Kerry, Cork, and Waterford.

| No. | Description | Feet | |-----|--------------------------------------------------|------| | 1. | Coal Measures | + 2000 | | 2. | Carboniferous limestone | 1500 | | | Old Red Sandstone | |

No. 1. Over this district the Carboniferous limestone forms a nearly unbroken series of beds of gray limestone, sometimes compact, sometimes crystalline, generally in very highly-inclined positions, and often so traversed by slaty cleavage as to have its stratification entirely obscured. It occurs only in the plains and bottoms of the valleys.

No. 2. Directly on the upper beds of the limestone occur black indurated shales, likewise traversed by slaty cleavage, but never making good roofing-slate; higher up, these alternate with greenish or olive-coloured fine-grained grits and flags; and among these, or above them, occur two or three thin bands of coal, together with abundance of coal plants. The shales have often curiously concretionary globular forms, of one or two feet in diameter, appearing in them, piled one over the other; a single spheroid sometimes embracing parts of two or more beds. Except weathering into these singular spheroidal forms, the shales do not appear different from those which are not concretionary. These Coal Measures are commonly highly-inclined and contorted, and often inverted, and the coals are not only changed into anthracite, but squeezed and crushed so as to be only got in small dice-like fragments. The regularity of the beds is also interfered with, so that beds of which the original thickness was probably a couple of feet or so, have now for many yards only one or two inches, and then suddenly expand into large pockets of coal 20 or 30 feet in thickness. Coal-mining here is conducted like vein-mining.

Clare, Limerick, Tipperary, Kilkenny, &c.

| No. | Description | Feet | |-----|--------------------------------------------------|------| | 5. | Coal Measures | + 2000 | | 4. | Upper Limestone | 250 to 1000 | | 3. | Calp or Middle Limestone | 400 to 1000 | | 2. | Lower Limestone | 1000 | | 1. | Lower Limestone shale | 50 to 150 | | | Old Red Sandstone | |

No. 1 is everywhere the same as before described.

No. 2 is a series of thick gray limestones, generally light-coloured, sometimes crystalline, sometimes compact; large parts of it are magnesian, sometimes becoming a true dolomite. In some parts of the district some of the beds become Oolitic as the Bath stone, still, however, retaining their gray colour. In some places, especially in Limerick, contemporaneous traps and trappean breccias are interstratified with these beds and with the upper or yellow part of the Old Red Sandstone below them.

No. 3. Black limestones, sometimes very earthy, interstratified with black shales, that become in some places more important than the limestones. The limestones of this group are usually unfit for burning into lime. Chert bands and nodules are very abundant in the Calp.

No. 4. Thick and thin bedded crystalline and compact limestones of various colours, but usually light-coloured. Chert bands and nodules are also abundant occasionally.

No. 5. The Coal Measures are exactly the same as those previously described in Kerry and Cork, except that they are little contorted, lying generally horizontal or nearly so, and the coal beds retain their thickness apparently unaltered,—this thickness, however, being rather inconstant between 6 inches and 2 or 3 feet. The fossils found in the lower part of these coal shales are marine—Goniatiites, Bellerophon, and Pecten papyraceus. Coal plants, however, are abundant in the higher part near the beds of coal. It is possible that these Coal Measures may be of the same age as the millstone grit of central and northern England.

North of Ireland.—As we trace the Carboniferous series from the central to the northern districts of Ireland, a still further change takes place always in the same direction; that is, always becoming more complicated and subdivided as we proceed from south to north. The typical rocks then become—

| No. | Description | |-----|--------------------------------------------------| | 7. | Coal Measures | | 6. | Millstone grit | | 5. | Upper Limestone | | 4. | Calp | | | Upper Calp shale | | | Calp sandstone | | | Lower Calp shale | | 3. | Lower Limestone | | 2. | Lower Limestone shale | | 1. | Yellow Sandstone and Old Red Sandstone |

1. The Yellow Sandstone of Dr Griffith, as shown in the north of Ireland, is interstratified with dark shales and gray limestones, containing common Carboniferous fossils in great abundance. It has also red beds of shale interstratified with it, but may perhaps be a rather different group from the yellow sandstones forming the top of the true Old Red Sandstone in the south of Ireland.

2. This group does not appear to differ in any respect from the Lower Limestone shale of the south of Ireland.

3. The Lower Limestone is also apparently just like that of the south.

4. The Calp becomes more purely an earthy deposit, and the shales are split up by a considerable group of sandstone beds in its middle portion, sometimes containing traces and thin seams of coal.

5. The Upper Limestone is probably the same as the Great Scaur Limestone of the north of England. These also are similar to the corresponding beds in Derbyshire and Yorkshire, shortly to be described.

Let us now turn to England, and trace in like measure the Carboniferous series from south to north.

South Wales and the Border Counties.—The rocks of the Carboniferous period may here be grouped as follows:

1. The Lower Limestone shale consists of dark earthy shales, occasionally interstratified with yellowish sandstones below, and always with thin flaggy limestones in its upper part. It seems therefore to graduate downwards into the top of the Old Red Sandstone, as well as upwards into the Carboniferous limestone.

2. Carboniferous limestone.—A great series of compact limestones, thick and thin bedded, of various shades of gray and red, interstratified with brown, gray, and red shales below, and with shales and sandstones (often red) in the upper portion. Thickness, 1800 to 2000 feet.

3. Millstone grit or Farewell rock.—A series of sandstones, hard, quartzose, white or gray, and near Bristol, red. Maximum thickness about 1000 feet.

4. Coal Measures.—An enormous series of alternations of many hundred beds of shales, sandstones, and coals, the latter varying from 1 inch to 7 or 8 feet in thickness. The total thickness of the whole group is not less than 7000 feet, and is believed in some places to be even as much as 12,000 feet.

Near Bristol it is thinner, and is divisible into three sub-groups, having a central band of hard sandstones called Pennant.

- Upper Coal Measures ........................................... 1809 - Pennant series .................................................. 1723 - Lower Coal Measures ........................................... 1665

This central band of sandstones is traceable also in South Wales by means of a hard quartzose sandstone called Cockshort rock.

In the Forest of Dean coal-field the thicknesses given above are diminished to about one-third, or—

Coal Measures. Millstone grit .................................................. 270 Carboniferous limestone ....................................... 480 Lower Limestone shale ......................................... 165

(Mem. Geol. Survey, vol. i., p. 129.)

Derbyshire, &c.—The base of the formation is not here seen, but we have the following groups:

1. The Carboniferous limestone is a series of pure pale-gray, thick-bedded limestones, with scarcely a trace of clay or shale interstratified with them, over large areas, and through a thickness of several hundred feet. On the southwest, however, towards Staffordshire, shales alternate with its upper portion. Over the centre and north of Derbyshire two contemporaneous beds of greenstone, called toadstone, are interstratified with the limestones. The thickness of these toadstones is sometimes as much as 100 feet, but generally 20 or 30.

2. Upper Limestone shale.—This is a series of beds of black shale, without either limestone or sandstone in all the central part of the district, and about 500 feet thick. It is not recognised as an independent group in the South Welsh district.

It is generally devoid of fossils.

3. Millstone grit.—Thick, yellow, white or brown sandstones, sometimes fine-grained, sometimes very coarse, containing quartz grains as large as peas. Separated into four groups of sandstones by three little intervening coal-seams and their associated shales.

4. Coal Measures.—Alternations of sandstones and shales, with interstratified beds of coal generally resting upon fireclay. The Lower Coal Measures in Derbyshire and Yorkshire contain many beds of hard sandstone called "ganister," and it is difficult to draw any decided boundary line between them and the Millstone grit.

Proceeding northwards from Derbyshire, we find a gradual change taking place in the arrangement and grouping of the beds mentioned above. The Coal Measures retain their characters, but the Millstone grit first becomes more separated by beds of shale and coal, while the Upper Limestone shale becomes split up by beds of sandstone above and of limestone below, and eventually likewise contains beds of coal; and, lastly, the limestone itself has its beds separated by shales and sandstones, which finally, as we go farther north, include beds of coal; so that the whole series becomes a great series of Coal Measures containing interstratified limestones in its lower part only. This change is perceptible by examining the rocks of North Yorkshire and Durham. (Phillips.)

1. The Great or Scaur Limestone, as described by Foster in Teesdale (Phillips' Manual, p. 163), consists of ten sets of beds of limestone from 7 feet to 130 feet in thickness, separated by as many sets of shale and sandstone varying from 12 to 240 feet thick, the total thickness of the whole being 1119 feet, with the bottom not seen.

2. The Yoredale series contains nine sets of limestone from 2 to 30 feet thick, with as many alternations of shales and sandstone from 17 to 70 feet thick, with occasional beds of coal, the whole being 544 feet thick.

3. The Millstone grit here contains one central band of limestone, called Feltop lime, between alternations of sandstone, shale with ironstone, and coal, having a total of 414 ft.

4. The Coal Measures of the Tyne district (Newcastle, &c.) are about 2000 feet in thickness, containing about 600 separate beds (or measures), and a total of about 60 feet of coal. The coal lies in many beds, two of which are 6 feet in thickness, and three others 3 feet and more. The Lancashire coal-field, containing higher beds than are to be seen on the Tyne, is more than double this thickness, or about 5000 feet, including 75 beds of coal over a foot thick (some being 6 feet), and a total thickness of 150 feet of coal.

Scotland.—The Carboniferous rocks of the country between Edinburgh and Glasgow may be judged of from the following section, of which the upper 600 feet is taken from the Monkland district, and the rest from that of Carlisle:

Red Sandstone (Carboniferous)

| Alternations of sandstones and shales with coal and ironstone | 1300 | | Limestone | 10 | | Alternations, &c., five beds of coal 4 feet thick, many others less | 16350 |

Forward | 17660 | Devon and Cornwall.—This district contains beds belonging to the Upper as well as the Lower Carboniferous series, but they are very anomalous and scarcely comparable with any degree of certainty with those of the rest of Britain. They consist of—

1. Culm Measures. 1. Shales and limestones, probably the Lower Limestone shale.

2. The shales, &c., over the Marwood sandstone group resemble more or less the Lower Limestone shales of South Wales, except that they are traversed by slaty cleavage, and have in their upper parts a dark-coloured limestone that may be a debased representative of the Carboniferous limestone.

3. The Culm Measures are a great series of alternations of shales (sometimes cleaved into slates), sandstones, and fine conglomerates, into a few beds of earthy anthracite or culm. Whether they are of the same age as the true Coal Measures is doubtful. They may perhaps have been deposited contemporaneously with part of the Carboniferous limestone, but under different conditions, and probably in water (fresh or salt) altogether separated from the seas of the north. Or if we suppose with Sir R. I. Murchison that the black limestone of group 1 represents the whole of the Carboniferous limestone, then the Culm Measures may be of the age of millstone grit, and possibly that of the coal-bearing rocks of the Kilkenny and the Kerry coal-field.

Midland Counties.—The Carboniferous rocks of the midland counties of England are by no means typical groups. They consist generally of the upper portion or Coal Measures only, resting unconformably on Silurian or still older formations. It is probable that during the time of the deposition of the Carboniferous limestone there was land existing where the midland counties of England now are, which land only became covered with water in consequence of a gradual depression taking place in the latter part of the Carboniferous period.

Belgium.—According to M. Dumont—

Systeme Condru-

1. Alternations of "ampelite" (sandstone) shale, and coal.

2. Gray sandstone, soft sandstone, and anthracite.

3. Gray shales, calcareous shales, dark limestone, and plagioclase iron ore (oligiste).

Carboniferous rocks occur in small detached localities in many other parts of Europe, but do not admit of description as typical rocks of the period. The fossils contained in them agree with those already mentioned, with just that amount of difference that might be expected to arise from the laws of geographical distribution.

North America: Nova Scotia.—According to Mr Dawson—

Upper Group.

1. Grayish and reddish sandstones and shales, with beds of conglomerate, and a few thin beds of limestone and coal. 3000 feet and more.

Middle of Good Coal Group.

2. Gray and dark-colored sandstones and shales, with red and brown beds, coal, ironstone, and bituminous limestone. 4000 feet and more.

Lower of Gysiferous Group.

1. Red and gray sandstones and conglomerates, and red and green marls and shales, with thick beds of gypsum and limestone. 6000 feet and more.

Altogether there is a thickness of more than 14,000 feet, without reaching any exact base, or arriving apparently at the very highest beds of the series. There are seventy-six beds of coal, of which, however, most are only 1 or 2 inches thick, and the thickest not more than 4 feet. (Dawson's Acadian Geology.)

Some of the beds of group 1, consisting of sandstones with variegated marls and gypsum, and a few beds of coal, were seen formerly by ourselves in Newfoundland, on the south shore of St George's Bay, and at the northern extremity of the Grand Pond. (Report on Geology of Newfoundland.)

United States.—According to Professor Rogers—

3. Upper Carboniferous or Coal Measure Group.

Coal Measures, alternations of sandstones, shales, and coals, like groups 2 and 3 of the Nova Scotia district, but thinning out westward, so as to be only 3000 feet in Pennsylvania, 1500 in the Illinois basin, and not more than 1000 in Iowa and Missouri.

Soft red shales and argillaceous red sandstones in Pennsylvania, 3000 feet.

In Virginia—

a. Blase, olive, and red calcareous shales, with thick red and brown sandstone.

b. Light-blue limestone, sometimes Oolitic.

c. Buff, greenish, and red shales, with sandstone.

Total thickness, 3000 feet.

In the Western States—

d. Gray and yellow sandstone.

e. Light-blue and yellow limestone, 1000 feet.

White, gray, and yellow sandstones, alternating with coarse siliceous conglomerates and dark-blue and olive-colored shales. In some places contains black carbonaceous slate, and a bed or two of coal. 2000 feet thick in Pennsylvania, thinning out to nothing in the north-west.

Australia: New South Wales.

5. Dark-brown shales, with impressions of plants, 300 feet and more.

4. Sydney sandstone, thick white or light-yellow sandstone, with quartz pebbles occasionally, and partings of shale, 700 feet.

3. Alternations of shales and sandstones, 400 feet.

2. Shales containing two or three good beds of workable coal 6 feet thick, 200 to 300 feet.

1. Wollongong sandstones, thick dark-gray reddish-brown, often calcareous, with large calcareous concretions, 400 feet and more.

---

1 The light-blue limestone mentioned above thickens toward the south-west and dies away to the north-east in Pennsylvania. This is only a part of the series, as there may be beds below No. 1, and others above No. 5.

Victoria.—The same formations as New South Wales. We may expect shortly to receive more definite information respecting them from Mr A. N. C. Selwyn and the geological survey under his direction.

In Tasmania similar rocks occur, similarly associated with a thin group of shales, containing one or two good beds of coal.

India.—We may shortly expect more definite information than we yet possess, from the labours of Professor Oldham and his staff, on the geological survey of that country.

PERMIAN PERIOD.

Typical Groups of Rocks.—Durham, &c.—According to Professor Sedgwick—

| Feet | |------| | 6. Red gypseous marls | 100 | | 5. Thin-bedded gray limestone | 80 | | 4. Red gypseous marls, slightly saliferous | 100 | | 3. Magnesian limestone | 500 | | 2. Marl slate | 60 | | 1. Lower Red Sandstone | 200 |

1. Is a coarse pale-red sandstone, resting unconformably on the Coal Measures, often containing large fragments of coal plants, that may have been drifted out of the Coal Measures, and sometimes fragments of coal.

2. Marl slate, a brown indurated fissile shale, with occasional beds of thin compact limestone.

3. Magnesian Limestone.—A singularly diversified mass of limestones, sometimes compact, at others crystalline, brecciated, earthy, globular, oolitic, cellular, &c.; some beds like piles of cannon or musket balls, others like bunches of grapes, &c.; some very hard, some quite friable, some thin and flexible. General colour, shades of yellow, sometimes red and brown.

Nos. 4, 5, and 6, are sufficiently described already; they are destitute of fossils, except a few traces of bivalves in No. 5.

Midland Counties of England.—A great series of red and variegated sandstones and conglomerates, with breccias containing angular fragments of trap and of Silurian and Carboniferous rocks, together with thick dark-red marls, and in some places mottled calcareous bands, like the cornstones of the Old Red Sandstone. The total thickness in many places exceeds 1000 feet.

Ireland and Scotland.—The red sandstones of Roan Hill, near Dungannon, containing abundance of *Palaeoniscus catopterus*, are probably Permain. Yellow magnesian limestones, exactly like those of Durham, and with many of the characteristic fossils previously mentioned, occur in patches at Artrée, county Tyrone, and at Cultra, near Belfast.

The red sandstones of Dumfries, with tracks of reptiles so beautifully figured by Sir W. Jardine in his *Ichthyology of Annandale*, may also possibly belong either wholly or in part to the Permian rather than the Triassic period.

South of Russia: Government of Perm.—According to Sir R. I. Murchison, the district of Perm exhibits so great a development of the rocks of this period as to induce him to select that name for it. These beds are said to be very various, but in one locality they have the following type:

- Conglomerate and sandstone. - Red sands and copper beds. - Sandstones, limestones, gypsum, and grit beds.

The limestones are often numerous, and contain fossils like those of the magnesian limestone of England and the Zechstein of Germany, while other beds contain Thecodontosaurus and fishes.

In Thuringia so great is the accordance with the British series, both in the rock groups and their included fossils, that Professor King in his monograph places them side by side as follows:

| Thuringia | North of England | |-----------|------------------| | Stinkstein | Crystalline limestone | | Rauchwacke | Brecciated limestone | | Dolomit | Fossiliferous limestone | | Zechstein | Compact limestone | | Mergel, or Kupfer schiefer | Marl-slate | | Rotho tolle Legende | Lower Red Sandstone |

Professor Sedgwick long ago pointed out the remarkable similarity of the fish in the "Mergel schiefer" and his Marl slate. (See Sedgwick's paper on *Mag. L. Trans. Geol. Society.*)

During the Permian period, and at its close, the part of the earth now occupied by Western Europe seems to have been more than usually affected by movements of elevation and disturbance, attended with consequent large denudation of the previously existing rocks. We are obliged, therefore, to look to other parts of the globe, where tranquillity reigned during the portion of time that elapsed at the close of the Primary and the commencement of the Secondary epochs, for the typical deposits during this part of the earth's history. Future research will probably be prolific of future discovery of records now unknown to us belonging to the Permian and Triassic periods. Some of these discoveries are even now being made, but many others will doubtless follow. As a consequence of this disturbance and denudation, the Permian rocks are frequently unconformable to the Carboniferous, and the Triassic to the Permian.

CHAP. II.—SECONDARY OR MESOZOIC EPOCH.

TRIASSIC PERIOD.

Typical Groups of Rock.—Germany—

| Feet | |------| | 3. Keuper | 1000 | | 2. Muschelkalk | 600 | | 1. Bunter Sandstein | 1500 |

1. The Bunter Sandstein, or "variegated sandstone," is a red and white sandstone interstratified with red marls and thin bands of limestone, sometimes oolitic, sometimes magnesian. This is the "Gres bigarré" of the French.

2. Muschelkalk.—A compact reddish-gray or yellowish limestone, rarely oolitic, but in some places magnesian, especially in the lower beds, which include beds of gypsum and rock-salt. It might accordingly be divided into two sub-groups:

a. Upper Muschelkalk, regularly-bedded limestone, more than 300 feet thick. b. Alternations of limestone, dolomite, marl, and gypsum or anhydrite, and rock-salt, 280 feet.

3. Keuper.—"Marnes irisées" of the French. Principally red and green marl, but is locally divisible into three sub-groups, namely:

a. Keuper sandstone, of a yellowish-white, sometimes green and reddish colour, containing calamites and other plants. b. Keuper marls, with gypsum and dolomite, containing coprolites, fish, and saurian bones, scales, and teeth. c. Lettenkohle (clay-coal) group, a dark-gray shale or gray sandstone, containing small irregular beds of impure earthy coal, with remains of Mastodonsaurus (Labyrinthodon), Gervillis, Posidonia, and Längula.

This latter group rests directly on the Muschelkalk, and... Geology seems, from its animal remains, to belong to it, but its plants are those of the Keuper.

Near Stuttgart, and in other parts of Germany, the Keuper sandstone is capped by a layer of sandstone breccia, full of the remains of saurians and fish in fragments, exactly like that known in England as the "bone bed." It is still doubtful whether this belongs more properly to the Trias or the Lias. Like the bone bed at the top of the Ludlow, it may perhaps be taken as an indication of a great gap in the series of beds.

In the Supplement of Sir C. Lyell before mentioned we have the latest intelligence regarding a set of beds which fill up the gap indicated by these "bone beds;" and, moreover, give us the true marine fossiliferous equivalents of the elsewhere fresh-water or unfossiliferous Keuper, and possibly also of part of the Bunter.

Near Hallstatt (south-east of Salzburg), on the north side of the Austrian Alps, and at St Cassian, on the south side, are a set of beds composed of red, pink, and white marble, from 800 to 1000 feet in thickness, and containing more than 800 species of fossils.

Underneath the Hallstatt and St Cassian beds are others called the Gutenstein and Werfen beds. They consist of—

| Feet | |------| | b. Gutenstein beds, black and gray limestone, alternating with red and green shale. | 150 | | a. Werfen beds, red and green shale and sandstone, with gypsum and rock-salt. |

It is yet doubtful whether these are only a lower portion of the St Cassian beds, or are to be considered as equivalents of the British or Lower Trias.

Over the St Cassian beds again come 2000 feet of white or greyish limestone, known as the Dachstein beds, and above these 50 feet of gray and black limestone with calcareous marls, called the Kessen beds. Each of these groups contain a peculiar set of fossils of a character which renders it uncertain whether they should be classed as Upper Triassic or as Lower Liasic groups.

We would press upon the reader's attention that we have in these beds one or two of the missing links that are to reward the researches of future geologists, and fill up the many gaps in our geological history.

England.—The Triassic rocks of England are anything but typical, notwithstanding that they occupy a greater surface than perhaps any other formation. The important central division, the Muschelkalk of Germany, is entirely wanting, as are the still more important Hallstatt and St Cassian beds. The labours of the Geological Survey of the last few years have shown following to be the groups in the midland counties, where the formation is best developed:—

3. Red and variegated marls. 2. White sandstone. 1. Red and mottled sandstone.

1. The Red and Mottled Sandstone has a base of "brick-red" sandstone, very fine grained and thick-bedded. Over this come reddish-brown sandstones, or red and white sandstones, with beds of marl, and thick, rather irregular bands of partially consolidated conglomerate, called "pebble-beds." Mottled calcareous concretionary sandstones, not unlike some varieties of "cornstone," occur occasionally in this "brown" division, often associated with the marls. The whole group seems to be locally represented by a dolomitic conglomerate, unless that should be referred rather to the Permian period.

2. The White Sandstone is a very persistent and well-marked group over a very wide area, forming the hill on which Beeston Castle (Cheshire) stands, and spreading through a great part of the midland counties of England. It is generally white, sometimes mottled with red, and is often used as a building stone, for which purpose it is occasionally sufficiently well adapted.

3. The Red and Variegated Marls contain irregular beds of sandstone, and almost invariably beds and veins and strings of gypsum, and frequently thick masses of rock-salt. In Cheshire, near Northwich, the following section shows a part of the thickness of these beds:—

| Feet | |------| | Upper strata (marl, &c.). | 127 | | 1st bed of rock salt. | 85 | | Indurated marl (locally called "stone"). | 90 | | 2d bed of rock salt. | 106 | | Indurated marls, with thin beds of salt. | 161 |

499

Over this thickness of 500 feet are other beds of marl, &c., before we reach the base of the Lias, and under them others before we should attain the top of the whitestone, so that the entire depth of the group must be 700 feet with, or 500 without, the salt.

An occasional set of beds of a pale-coloured sandstone, called by ourselves formerly the "Dove-coloured Sandstone," in the upper part of this group, contains fossil plants and fragments of reptiles, enabling us to identify this group, No. 3, with the Keuper of Germany. No. 1 is almost certainly the same as the German Bunter Sandstein, and the French "Gres Bigarré."

Ireland.—In the north, near Belfast, a considerable mass of red sandstones belong either to the Bunter sandstone or the Permian. Over them is a group of red and variegated marls, which, near Carrickfergus, contains beds of gypsum and rock-salt, of which the following is a section:—

| Feet | |------| | Red marls, with gypsum. | 510 | | Red salt. | 22 | | Marl and salt. | 26 | | Pure rock-salt. | 84 | | Mixed rock-salt. | 14 | | Pure rock-salt. | 39 | | Blue bands and freestone, &c. | 25 |

700

These have other beds of red marl above them, about 100 or 150 feet thick, over which is the base of the Lias. They in all probability therefore belong to group No. 3, and = Keuper of Germany.

THE OOLITIC OR JURASSIC PERIOD.

Typical Groups of Rock.—England.—If we arrange the whole series of the rocks of this period in their order of occurrence, in slightly different but neighbouring localities, we shall have the following list:—

| Feet | |------| | Portland, or Upper Oolite. | | 12. Purbeck beds... | 150 | | 11. Portland beds... | 170 | | 10. Kimmeridge clay... | 600 | | Oxford, or Middle Oolite. | | 9. Coral rag... | 180 | | 8. Oxford clay... | 600 | | Bath, or Lower Oolite. | | 7. Cornbrash... | 30 | | 6. Great Oolite... | 130 | | 5. Fuller's earth... | 130 | | 4. Inferior Oolite... | 230 |

| Feet | |------| | 1. Upper Calcar. grit. | | 2. Oolitic limestone. | | 3. Lower Calcar. grit. | | 4. Dark clay. | | 5. Kelloway rock. | | 6. Forest marble. | | 7. Bradford clay. | | 8. Freestone and rag. | | 9. Stonesfield slate. | | 10. Ragstone. | | 11. Freestone. | | 12. Pea grit. | A. The Lias.—Essentially a great clay deposit, with occasional bands of a peculiar compact argillaceous limestone near the bottom, and an argillaceous sandstone near the middle, with a loose sandy deposit at top connecting it with the group above.

1. Lower Lias.—At the top of the red marls of the Triassic Keuper group below is a little layer of hard sandstone full of fragments of bones and teeth of reptiles and fish. In some places bones of Keuper reptiles have been seen in it, and the layer therefore referred to the Trias; in other places it is full of undoubted Lias fossils. It is probable that there is in reality more than one bone bed, the diminutive representative of the great passage beds between the Trias and the Lias, 2000 feet and more in thickness, which are found at Dachstatt and Kressen.

In some places the black shales of the Lower Lias rest on the red marls without any bone bed and without any limestone, while in others a group of limestones, interstratified with clays, having a thickness of 20 to 50 feet, is seen. Over these limestones occur the ordinary blue clay of which the Lower Lias is generally composed.

2. The Marlstone is a well-marked division of the Lias, being more arenaceous, though still fine-grained, and often bound by calcareous or ferruginous cement into a hard stone. In Gloucestershire it is divisible into the hard "rock bed" above, and the sands, often rather argillaceous, below.

3. Upper Lias.—This consists of a great thickness of blue clay, over which are some brown and yellow sands, hitherto classed with the Inferior Oolite, but separated from it on good palaeontological evidence by Dr Wright of Cheltenham, and called by him Upper Lias sands, capped by a particular band called the "Cephalopoda bed," from the abundance of those fossils which it contained.

The lithological type and the characteristic assemblages of fossils are applicable to the Lias throughout England from Lyme Regis to Whitby, if we allow for some variations in thickness and in the character of the minor groups of rock, and for a local distribution in the fossils.

B. The Lower or Bath Oolite, composed of the four groups called,—4. The Inferior; 5. Fuller's earth; 6. The Great Oolite, and 7. The Cornbrash.

4. The Inferior Oolite near Cheltenham, where it contains its greatest development, consists of— a. The Pea grid, a pisolithic limestone, made up of flattened oval concretions rather larger than peas, sometimes 40 feet thick; b. The Freestone, a fine pale-coloured oolitic or shelly limestone, 164 feet thick, containing a bed of marl 7 feet thick near the top; c. The Ragstone, a brown sandy limestone, sometimes hard, sometimes incoherent, 38 feet thick.

In the Cheltenham district even the subdivisions of the Inferior Oolite mentioned above have their lists of peculiar and characteristic fossils. (Memoirs of the Geological Survey, 1857; Mr Hull On the Geology of Cheltenham.)

5. Above the Inferior Oolite comes in the Gloucestershire district, a series of blue and yellow shales, clays, and marls, some of which are of the peculiar kind of clay called Fuller's earth, the name assigned to the group. Interstratified with these are occasional bands of limestone.

The maximum thickness is about 150 feet, rather rapidly diminishing in all directions.

6. Great Oolite.—This, like all the other oolitic groups, except the clays, has a very variable lithological character. Mr Lycett says that near Minchinhampton it is made up of weatherstones, sandstones, and limestones; the weatherstones, shelly calcareous sandstones, being always at the base of the group, but passing laterally into sandstones, which are commonly covered by limestones, while the weatherstones have never any of the limestones above them. (Jour. Geol. Soc., vol. iv.; and Palaeontolog. Soc., 1850.) Mr Hull divides the Great Oolite near Cheltenham into two zones,—a. The Under zone, a variable series of sandy flags, "slates," and blue limestones, with white oolitic freestones, showing much oblique lamination. The flaggy limestones, and sometimes the thick-bedded ones, split in some places into very thin slabs, which are called, though erroneously, "slates." The Stonesfield slate, so celebrated for its terrestrial reptiles and mammalian remains, belongs to these beds, and it might therefore give its name to the zone. The Collyweston slate belongs to this group; thickness, 35 feet. b. The Upper zone is well marked in Gloucestershire by the occurrence of a bed of marl at its base, and a band of hard white limestone at its summit, the intermediate beds being oolitic limestones, sandstone, or sandy limestone, greatly marked by oblique lamination; thickness, 100 feet. (Memoirs of the Geological Survey, 1857.)

7. Cornbrash group.—This is a very variously composed set of clays, sands, and limestones, containing local divisions, such as the Bradford clay, the Forest marble, and the Cornbrash itself.

The Bradford clay is a blue unctuous clay occurring at Bradford, and extending for a few miles around it; it is never more than 40 or 50 feet in thickness; locally full of Apiocrinites Parkinsoni (rotundus). The Forest marble (so named from Wychwood Forest) is composed of coarse fissile oolite, with much oblique lamination, hard shelly limestones, blue marls and shales, yellow siliceous sand, with large spheroidal blocks of limestone, and fine oolitic freestone. It is rarely more than 40, never more than 80, feet thick. The Cornbrash is generally a rubbly cream-coloured limestone in thin beds, always nodular and concretionary, each fragment having a deep red coating. Not more than 15 feet thick.

The foregoing description of the Bath Oolite is applicable, with more or less accuracy, to all the country south of the Humber. Proceeding into Yorkshire, however, a very remarkable change takes place both in the rocks and the fossils.

The little insignificant-looking band of the Cornbrash continues lithologically and palaeontologically the same; below this, however, instead of limestones, there is a great mass of shale and sandstone, with a band of shelly oolite in the centre, and, underneath all, ferruginous sands and calcareous sandstones that may either represent the Inferior Oolite or the Upper Lias sands.

Professor Phillips gives the following as a condensed account of this Yorkshire type:

| Description | Feet | |--------------------------------------------------|------| | Shelly Cornbrash limestone of Gristhorp and Scarborough | 10 | | Sandstones, shales, ironstones, and coals of Gristhorp, Scarborough, and Scalby, including some calcareous shelly bands | 200 | | Shelly oolite, and clays of Cloughton and West Nab | 60 | | Sandstones, shales, ironstones, and workable coal of the Peak, Stanhope Dale, and Haiburn Wylie | 500 | | Irony sandstone and subcalcareous beds, with bands of shells and plants | 60 |

Some Equisetites are found erect in these beds, and everything tends to show that we have in this type a true secondary coal formation of the Oolitic period, in addition

---

1 We have formerly pointed out the advisability of confining the term "slate" to those rocks of which the thin plates are the result of "cleavage," not of deposition. Geology, to that primary coal formation formed in that which is distinctively called the Carboniferous period.

C. The Oxford or Middle Oolite consists of two principal groups—the Oxford Clay and the Coral Rag.

8. The Oxford Clay is generally a dark blue clay, sometimes dark gray, approaching to black. In its lower portion it has some beds of tough calcareous sandstone, with brown sands called Kelloway rock, from a place in Wiltshire. This Kelloway rock appears to be wanting in the midland counties, but reappears in Yorkshire with the same characters and fossils. The maximum thickness of the Kelloway rock is 80 feet. That of the whole Oxford clay, including it, cannot be less in some places than 600 feet.

9. The Coralline Oolite or Coral Rag.—Like all the other calcareous or arenaceous groups of the Oolite, this is very irregular, and subject to great variations in character and thickness. There is a pretty close general resemblance in the Yorkshire and Wiltshire types, while in the intermediate district the whole group seems to disappear. It may be divided into three sub-groups,

| Feet. | |---| | a. Upper Calcareous grit, maximum thickness 60 | | b. Coralline oolite, " 50 | | c. Lower Calcareous grit, " 80 |

a. The lower beds in Yorkshire are a series of gray marly sandstones, 70 feet thick, passing up into cherty limestone, covered by sands full of great calcareous concretions, capped by strong calcareous sandstones.

b. A variable group of irregular masses of nodules made of corals compacted together, often earthy, and connected by blue clay, passing into blue crystalline limestone, alternations of hard shelly oolite, and soft perishable limestone, and in Wiltshire a rubbly nodular oolite, sometimes pisolitic.

c. The upper group obscurely indicated in the south is, in the north, like group a, but more ferruginous and less cherty, passing up by intercalation into the Kimmeridge clay above. (Phillips.)

D. The Portland or Upper Oolite is composed of three principal groups, each capable of subdivision into two or three sets of beds.

10. The Kimmeridge Clay is in some places a dark gray shaly clay, in others brownish or yellowish, and containing bands of sand, or of calcareous grit, or ferruginous oolite, and layers of nodules of septaria. In some places, especially in the district about the Isle of Purbeck, it becomes very bituminous, and the bituminous shale sometimes passes into layers of "brown shaly coal." Layers of a particular kind of oyster, called the Ostrea deltoidea, occur abundantly in some places, always appearing "in broad continuous floors, parallel to the planes of stratification, the valves usually together, with young ones occasionally adherent to them, and entirely embedded in clay, without nodules or stones of any kind, and without any other organic remains in the layers." (Phillips.)

11. The Portland beds.—These, like most of the other members of the Oolitic series, have a variable composition, consisting of sands and sandstones below, becoming calcareous and passing into oolitic limestone above. They are therefore divisible into

| Feet. | |---| | a. Portland stone, consisting of white oolite and beds locally termed "stonebrash" and "roche," &c., interstratified with clays, and containing layers of flint, about 90 to 100 | | b. Portland sands, consisting of brown or yellow sands and sandstones, full of green grana, like those afterwards to be described in the Greensands, about 80 |

12. The Purbeck beds are remarkably distinguished from the Portland, on which they rest, by being chiefly of fresh-water origin. They contain, however, some marine species, which are allied to Oolitic more closely than to any other types. Edward Forbes therefore detached them from the base of the succeeding formations, and placed them at the top of the Oolitic series. They are also distinguished from most other aqueous rocks by containing one or two beds of "vegetable soil," called by the quarrymen "dirt beds," with the stems of trees and cycadoid plants still erect, and the trunks of trees prostrate alongside of them. This clearly points to a tranquil and gradual elevation of the surface of the rock into dry land, the growth of a forest through hundreds or thousands of years, and its as tranquil and gentle submergence beneath some stagnant water without sufficient current to disturb the soil or carry off the buried plants.

Edward Forbes divides the Purbecks of Dorsetshire into three groups, each characterized by a peculiar assemblage of organic remains, without any other very marked distinction between them, and with no sign of any physical disturbance or denudation.

a. The lowest division, 70 or 80 feet thick, consists of calcareous flags, marls, and limestones, with cypridiferous shales and some siliceous bands, with one large and two or three smaller "dirt beds" near its lower portion. These are all either fresh-water or aerial, except 20 feet in the centre of the group, which are brackish water deposits, containing Rissoa (Hydrobia), Protocardium, and Serpula.

b. The Middle Purbecks, 40 or 50 feet thick, consist first of shales and limestones with thick bands of cherty stone, having impressions of leaves and many fresh-water shells; then the conspicuous "cinder bed," a great heap of small shells of Ostrea distorta, over which are other limestones and shales, some fresh-water, some brackish, and some purely marine, containing yet undescribed species of Pecten, Modiola, Avicula, and Thracia, together with a Protocardium distinct from that in the lower beds. Many fish—Lepidotus and Microdon radiatus—and reptiles of the genus Macrotyphus also occur. It is in a little band not more than 6 inches thick, about 20 feet below the "cinder bed," that the very remarkable discoveries of a number of remains of mammalian animals belonging to several genera and species have been made. (Lyell's Supplement.)

c. The Upper Purbecks, 20 or 30 feet thick, are another series of beds full of fresh-water shells, distinct from those below, and new forms of fish. The fresh-water snail-shells are sometimes so abundant as to form a hard limestone, much used formerly as Purbeck marble.

It is remarkable that the fresh-water shells have a much closer resemblance to those living at other and more recent periods, or those now existing, than the marine species have. The three changes of life in this small group of Purbecks appear to be due solely to lapse of time, and to those slow and gradual changes in the physical geography of the district which took place, and not to any sudden or violent revolutions or disturbances of which there is no trace.

Ireland.—The Oolitic series is represented in Ireland by a few thin beds of Lias only, not exceeding thirty feet in thickness, resting on the summit of the red saliferous marls of the Trias of the county of Antrim. It contains, however, a considerable abundance of characteristic Lias shells.

Scotland.—On the west coast, opposite the north-east of Ireland, Lias is found also in Scotland, together with Oxford clay, and other representatives of the Oolitic series;

1 Professor E. Forbes mentions one set of beds as curiously dilated and disturbed, apparently by causes not affecting the beds below; but this band of local disturbance is included in the lower division, and is not accompanied by any change in the species, while, on the other hand, the great changes in the species take place at certain lines where there is no lithological or petrological boundary whatever. (Report of British Association, 1850.) GEOLOGY.

while on the east coast at Brora, &c., representatives of the Yorkshire oolites are found, containing also impure coal.

The series of rocks deposited in the British Islands during the Oolitic period is so complete, both petrologically and palaeontologically, that they serve as a type for those known all over the world. In Europe, the term Jurassic is commonly used instead of Oolitic; the Jura mountain being principally composed of rocks belonging to this period. In tracing the rocks across Europe, differences, both lithological and palaeontological, occur, as might be naturally expected; but on the whole a wonderful similarity in both characters extends over very large areas.

It will perhaps be most useful to give a few of the foreign synonyms of the different rock groups adopted by different Continental geologists.

A 1. LOWER Lias.—Terrain sinémarien, grès du Luxembourg, calcaire de Valognes, grès de Lincksfeld, Gryphitien kalk. Lower black Jura.

A 2. MARLSTONE.—Terrain liasien, marne de Balingen, amaltheen ton, nummulalien mergel. Middle black Jura.

A 3. UPPER Lias.—Terrain toarcien, schistes de Bell, Posidoniomya schiefer, Jurassien mergel, Apallius ton. Upper black Jura and Lower brown Jura.

B 4. LYESTON OOLITE.—Terrain Bajocien, calcaire Lodonien, calcaire à polypiers marines vénusiennes, Eisen-Rogenstein discoliden mergel. Middle brown Jura.

B 5. FULLER'S EARTH; G. GREAT OOLITE; and T. CORNERASH.—Terrain Bathoien, calcaire de Caen et Ranville, Parkinson Bank. Part of brown Jura.

C 8 a. KELLOWAY ROCK.—Terrain Callovien, Oxfordien inférieur. Part of brown Jura.

C 8. OXFORD CLAY.—Terrain Oxfordien, terrain argovien, terrain à chailles, oraten ton, Impressa kalko, Spongiten layer. Part of brown Jura and Lower white Jura.

C 9. CORAL RAG.—Terrain corallien, schistes de Nuthaim, calcaire à néfrines. Middle white Jura. (The lithographic flags of Solenhofen are believed to be in this group.)

D 10. KIMMERIDGE CLAY.—Terrain Kimmeridgien, argiles noirs de Houlleur, marne de Banné, calcaire à astarteis. Part of the terrain portlandien of the geologists of the Swiss Jura, who call it lower part Terrain Séquanien; part of Upper white Jura.

D 11. PORTLAND BEDS.—Terrain portlandien, Upper white Jura, calcaire à tortues de Solcure.

D 12. PUNCHED BEDS.—These do not receive any exact synonym either in Pictet or in Vogt, the only two authorities accessible to me.

In other parts of the world the rocks of the Oolitic (or Jurassic) period appear chiefly in their Yorkshire type—that is to say, as sandstones and shales with beds of coal and ironstone, or as Oolitic Coal Measures. Sir Charles Lyell gives a brief description of the Oolitic coal-field of Richmond in Virginia, which has one bed of coal forty feet thick. In India also coal occurs in beds, some of which contain ammonites, shells, and plants very similar to those found in the Oolitic rocks of Britain.

One of the most remarkable localities for rocks of the Oolitic period to occur in, with fossils very closely allied to those of Europe, is the Arctic regions. Captain M'Clin- tock brought home several fossils from the Arctic regions, consisting of ammonites and other shells, closely analogous to Oolitic species; and Captain Sir E. Belcher brought part of the remains of an ichthyosaurus from the same regions.

The questions thus raised as to the climate of the globe, when cephalopods and reptiles, such as we should expect to find only in warm or temperate seas, could live in such high latitudes, are not very easy to answer.

CRETACEOUS PERIOD.

It is perhaps doubtful whether it would not be more advisable to divide the Oolitic period into two, calling the first portion Liassic, and treating it by itself. It is still more doubtful whether it would not be advisable to do the same with that on which we are now commencing, and treat the early part of the period as a distinct one, under the name of the Neocomian, or some other designation. For the present, however, it will be best to follow the classification adopted by Sir C. Lyell and others, calling the whole Cretaceous, but dividing the series of rocks into two strongly-marked divisions, called Lower and Upper, or the period of time into Earlier and Later Cretaceous.

TYPICAL GROUPS OF ROCK.—S.E. ENGLAND, N.W. FRANCE, BELGIUM, &c.—The following is the entire series of rocks deposited during the great Cretaceous period in this area:

| Feet | |------| | 8. Maestricht and Faxoe beds, Pisolithic chalk | 100 | | 7. White chalk, with flints | 500 | | 6. White chalk, without flints | 600 | | 5. Chalk marl | 100 | | 4. Upper Greensand | 100 | | 3. Gault | 150 | | 2. Lower Greensand | 850 | | 1. Speeton clay | 60 | | 0. Neocomian | 1300 |

This classification is derived from the study of different parts of the area lying between Yorkshire and Orleans, and Dorsetshire and Denmark. As happens in other cases, there is no place where the whole series is present at once, and some of the members are very local and inconstant. The middle part of the Upper Cretaceous series is the most constant and best-marked part of the group, giving us generally an easily recognisable geological horizon or band of demarcation between the beds below and above it.

We saw that at the close of the Oolitic period fresh-water deposits began to prevail within the area we principally contemplate. This involves the existence of large spaces of dry land in the neighbourhood, some of the surfaces of which have even their "soils" still preserved. It appears that a very large portion of the earth's surface must have been converted into dry land at this time in the neighbourhood of our area, for we have, in the commencement of this period, evidence of the existence of a great river, and the earliest deposit of this period appears to have been formed by the matter thrown down at the mouth of this river, and to be in fact a fossil delta as large as that of the Ganges or Mississippi. As, however, marine depositions must have been taking place in some other localities, it is to these that we should look if we wish to carry on our history with equilalent data; and it is believed that certain marine rocks, known as Neocomian, from their occurring at Neufchâtel (Neocomiensis) in Switzerland, are those which were the contemporaries of our fresh-water beds.

We will, however, first describe the beds of our own area, and take separately the Lower Cretaceous or Neocomian beds to begin with.

1. The Wealden beds, so called from their now forming a district known as the Weald of Kent and Sussex, consist of a great series of sandstones and shales, with a few beds of limestone and ironstone occasionally, often full of large fragments of drift-wood, and of the remains of freshwater shells, and of some fresh-water and some land animals (reptiles). In general appearance the Wealden rocks not unfrequently resemble some of the Coal Measures of the true Carboniferous period.

The Wealden rocks are commonly divided into two groups:

| Feet | |------| | b. The Weald clay | 280 | | a. The Hastings sand | 1000 |

These distinctions, however, seem hardly to be carried

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1 The exact position of the Speeton clay is a little uncertain. Professor E. Forbes, in Johnston's Physical Atlas, placed it at or below the base of the Lower Greensand on palaeontological evidence alone. out by any precise line of demarcation. The lower beds are more arenaceous, and the upper more argillaceous; but great beds of clay occur interstratified with the sandstones of the Hastings sands, and beds of sandstone with the clays of the Weald clay. It is probable that these beds change their character laterally as well as vertically, great banks of sand and large deposits of mud having been formed side by side. The sandstones are sometimes impregnated with carbonate of lime, so as to become calciferous grits; and small beds of limestone, forming Petworth or Sussex marble, chiefly consisting of fresh-water snail shells (Paludina), occur here and there. Local names are given to the different parts of the Wealden series in different places, as Ashburnham beds, Worth sands, Tilgate beds, Horsham beds, &c. (Phillips.)

2. The Lower Greensand was formerly considered the base of the Cretaceous series, separated only by the occasional bed of clay called Gault from the Upper Greensand. When the Gault is absent, and the Upper rests on the Lower Greensand, it is difficult to separate them by any lithological distinctions, but when they are separated they are found to be very distinct palaeontologically.

Where best shown (as at Atherfield, Isle of Wight, and Hythe, Kent; Fitton, Forbes, and Ibbetson, Jour. of Geol., vols. i. and iii.), the Lower Greensand is found to be a great series of alternations of sands, sandstones, and clays, with occasional calcareous bands. The calcareous sandstones form hard bands, known as Kentish rag; the clays are sometimes excellent fullers' earth, 60 feet in thickness, and are most abundant in the lower part of the formation, the upper being almost entirely sands. The general colour is dark-brown, sometimes red, and the sands are often bound together by an abundance of oxide of iron, from which the formation was formerly called Ironsand. It derives its name of Greensand from the occurrence of a number of little dark green specks (silicate of iron), which are sometimes so abundant as to give a greenish tinge to some of the beds; but the term "green" is generally quite inapplicable as a description, though it still remains as a commonly received name. The whole formation in Britain is very various in character. Its maximum thickness is 843 feet.

The beds immediately above the Wealden show sometimes a sort of passage lithologically, as if partly made up of those below, while the fossils are quite distinct, being entirely marine. It appears that a depression had taken place and allowed the sea to flow over the area which had been previously covered with fresh water. The change may thus be one of conditions rather than one of great lapse of time—a supposition strengthened by the fact of the bones of the *Iguanodon Mantelli* being found in the Lower Greensand, showing that that great reptile still lived on some neighbouring land, and that an occasional carcase of it was swept out to sea.

2a. The Speeton clay of Yorkshire, a local band of dark clay, is almost certainly of the same age as the Lower Greensand, if not, as thought by Professor Forbes, a little older than it.

Switzerland.—The rocks of Neuchâtel in Switzerland, which are looked upon as one of the best continental types of the beds deposited during this part of the Cretaceous period, are the following:

| Bed | Description | |-----|-------------| | 1. Lower yellow limestone | 22 feet | | 2. Blue marl | 32 feet | | 3. Yellow limestone, in broken beds | 22 feet | | 4. Yellow limestone, with siliceous masses | 43 feet | | 5. Yellow limestone, at least | 130 feet |

These beds rest unconformably on the beds of the Portland Oolite. (D'Arcy, vol. iv., p. 556.)

France.—D'Arcy gives the following as the type of the rocks of this period in the basin of the Seine:

- Green and ferruginous sand. - Clay, with Pterodactylus and *Eoxygenia* sinuata. - Variegated sands and sandy clays, with iron ore. - Clays, with oyster shells, &c. - Neocomian limestone and blue marl. - White sand and ferruginous sand, with iron goosends.

He says that these groups overlap each other from east to west, but that the upper group (C) also spreads much more widely than the rest from north to south.

The following continental names for groups of rock belong to this part of the period, being more or less nearly contemporary with Lower Greensand:—Hils clay and Hils conglomerate; Biancone; Spatangus and *Exogyra* limestone; Marls of Hautvive; Terrain Urgonien, or "premier zone de rudistes;" and Terrain Aptien, or argile à plicatures of D'Orbigny; the Hippurite limestone, &c.

Upper Cretaceous Beds.—We may now proceed to the examination of the Upper Cretaceous beds of our original area.

3. Gault.—This is a stiff dark-gray, blue, or brown clay, often used for brick-making. It can be seen very well at Cambridge and at Folkestone, but is by no means invariably present. The shells in it are often beautifully preserved, having been well packed and protected from atmospheric or other influences.

Mr Sharpe was inclined to the opinion that the sands of Blackdown were of the same age as the Gault, being the littoral deposits of the same sea, in the deeper parts of which the clay was deposited.

4. Upper Greensand.—This set of beds often resembles the Lower Greensand in lithological character, but the same caution is to be used in taking its designation for a name only, and not for a description. The sands are by no means always green, and other sands, especially some Tertiary sands, are to be found quite as green, or greener, than those which have received the name of Greensand. Beds and concretionary masses of calcareous grit occur in it, sometimes called firestone, sometimes malm rock. Concretions, probably coprolitic, containing phosphate of lime, also occur, and are valuable to the agriculturist. It has been surmised that the Upper Greensand may be in part a shore deposit, and therefore contemporaneous with, rather than preceding, the lowest beds of the chalk, but wherever the two are together, we always find the Upper Greensand underneath the Chalk Marl.

5. Chalk Marl.—The top of the Upper Greensand becomes argillaceous, and passes upwards into a pale buff-coloured marl or argillaceous limestone, sometimes of sufficient consistency to be used as a building stone. This in its higher portion begins to lose the argillaceous character, and gradually passes into the soft white pulverulent limestone familiar to every one as chalk.

6. White Chalk without flints.—This is a great mass of soft and often pulverulent limestone, thick-bedded, the stratification often obscure, partly by the obliteration of the bedding planes, partly by the abundance of quadrangular and diagonal joints, the surfaces of which are often weather-stained, dirty-green, or yellow. Nodular balls of iron pyrites, radiated internally, are frequent in it, and produce rusty stains about the rock.

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1 M. Renevier, after a detailed comparison of the British and continental rocks, determined that the Lower Greensand of England was strictly contemporaneous with the Aptian beds, and therefore not according to him Neocomian, of which he says the Urgonian is the upper part. We should be disposed, however, to give a wider sense to the term Neocomian (in default of a better), and to include in it all beds of an age intermediate between the Purbecks and the Gault. If M. Renevier be right, it is probable that the Urgonian and other Neocomian beds of Switzerland, &c., are the exact marine representatives of the fresh-water Wealden series. 7. White Chalk with flints.—There are no lithological distinctions between the Lower and Upper Chalk, except the occurrence in the latter of rows of nodules of black flint, and occasionally of seams and layers of the same substance. These occur either along the planes of stratification or parallel to them, so that they point out clearly the original bedding of the rock.

It is rare to find, either in the Upper or Lower Chalk, anything but pure limestone or pure flint. Little pebbles, however, sometimes occur in it, probably carried by the roots of plants; and in a cliff a little east of Dieppe, we once observed in the heart of the Upper Chalk a little band about 8 inches thick and 20 feet long of brown clay or marl, perfectly interstratified with the chalk. This was quite distinct from the seams and irregular patches of sand which may now and then be seen in the chalk, having been washed in subsequently from the drift on the surface, along the open joints and fissures, which are formed in it, as in all limestones, by the action of acidulous water along the original joints of the rock.

Although the Chalk and the Carboniferous limestone are so different in texture and induration, there is yet a certain resemblance in the forms of the country they produce. Their hills have equally broad undulating grassy downs, the escarpments of which are quite smooth in the chalk; while they are notched into steps in the mountain limestone. Their valleys are equally marked by scours, and tors and pinnacles, as any one may see by comparing the forms of the rocks on the sides of the valley of the Seine with those in the valleys of Derbyshire. The forms are, of course, bolder, larger, and more durable in the latter than the former.

8. Maestricht or Pisolithic Chalk.—At Mendon and Lavernines, and in other parts of the north of France, there occur curious banks of a white Pisolithic limestone, resting apparently in hollows of the Chalk, not always on exactly the upper portion of it, and being therefore apparently slightly unconformable to it. It occurs also sometimes on the same level as the lower beds of the Tertiary rocks about it. The fossils are rather peculiar, but some of them are Cretaceous, while none I believe are Tertiary.

Near Maestricht in Holland, also, the Chalk with flints (No. 7) is covered by a kind of chalky rock with gray flints, over which are some loose yellowish limestones, without flints, and being sometimes almost made up of fossils.

Similar beds containing some of the same fossils occur also at Faxoe in Denmark.

North of Ireland.—The Chalk of the north of Ireland is generally a rather hard compact stone, and usually goes by the name of "the White Limestone." It contains flints and a large assemblage of the characteristic fossils. Its thickness, however, rarely if ever exceeds 150 feet. Underneath it occur occasionally some beds of a whitish sandstone speckled with green, very much resembling some of the beds of greensand in the S.E. of England. Professor E. Forbes, however, once remarked to us that he thought it was more nearly of the age of the gault from its fossils. It is called in the country "Mulatto stone." Its thickness is rarely more than 15 or 20 feet.

**CHAP. III.—TERTIARY EPOCH.**

**Preliminary Observations.**

The nomenclature of the Tertiary periods proposed by Sir C. Lyell, and now all but universally adopted, is more systematic than that of the Primary or Secondary periods. It is based on the gradual increase of recent (i.e., living) species in the newer rocks. The earliest of the periods is termed Eocene, from the Greek words ἑοστός and ἐννεάς, signifying the dawn of the recent; the second, Miocene, from μικρός, the minority; the third, Pliocene, from πλεῖον, the plurality of recent species; and the next, Pleistocene, which expresses the recency of the great majority of the species.

To these we may add the present period itself, which we may perhaps most conveniently designate as the Recent or the Human Period.

The adoption of this principle of classification was rendered more necessary in the case of the Tertiary than the preceding epochs, from the nature of the physical conditions of Western Europe, on the structure of which our classification is chiefly based.

In the primary and secondary epochs, the part now occupied by Western Europe seems to have always contained more sea than land, and the rocks deposited are accordingly so widely spread as frequently to overlap and rest one upon the other. We can therefore often determine their order of superposition by their geognostic relations only; that is, by actually tracing each group of beds till we find it plunging under the superior group on the one side, or till the inferior group rises up to the surface from underneath on the other. When, however, we come to examine the Tertiary rocks of the same area, we find them more isolated and occurring in smaller and more detached patches, each patch ending before it comes in contact with the rest, so that their order of superposition can rarely be determined by simple inspection. To take a conspicuous instance at once:—The Chalk of the S.E. of England is continuous with that of France and Belgium, and no mistake could possibly be made as to the relative position of the beds above and below it. The Oolites below the Chalk are even still more extensive, and can be traced both geognostically and palaeontologically. The Tertiary beds above the Chalk, however, form isolated districts in the hollows of the Chalk, one being called the Hampshire basin, another the London, and a third the Paris basin; and if we wish to determine whether the beds of these three districts are of the same age, or whether one be older than another, it is obvious that we can no longer employ the positive evidence of an inspection of their superposition, but must have recourse either to the petrographical evidence of their being made exactly of the same kinds of rock occurring in the same order, or to the palaeontological evidence of their containing the same assemblages of fossils occurring in the same order; or if neither rocks nor fossils were the same, then we should have to fall back on the general rule or principle just spoken of, and see which contained an assemblage of fossils having the greatest approximation to living forms, and this in the case of Tertiary rocks is most easily determined by the relative percentage of actually existing species.

**THE EOCENE PERIOD.**

**Typical Groups of Rock.—S.E. of England, London and Hampshire Basin—**

| Series | Beds | Feet | |-----------------|-------------------------------|------| | Upper | | | | 8. Hempstead | d. Corbula beds | 25 | | | c. Upper fresh water and estuary marls | 40 | | | b. Middle | 60 | | | a. Lower | 90 | | | | | | 7. Bembridge | c. Lower marls | 115 | | | b. Oyster bed | 25 | | | a. Limestone | |

Carry forward, 290

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1 That the shallow furrow of the Straits of Dover has been worn down a little way below the level of the sea into the body of the Chalk, does not, of course, affect this assertion. The Lower Eocene Group.

The surface of the chalk on which the Eocene beds rest is generally eroded into hollows and undulations, showing a marked but not a very wide unconformity, as when the Chalk is greatly tilted, the Lower Eocene beds partake of the disturbance to an equal amount.

1. Thanet Sands.—Light-coloured quartzose sand, mixed in the lower beds with much argillaceous matter, but never passing into actual clay; containing occasionally dark-green grains like those mentioned before in the Greensands. It rests almost invariably on a stratum of Chalk flints, from which the chalk seems to have been washed away without wearing or fracturing the flints, and these are of a bright olive colour externally, by which they may be recognised in other beds (Tertiary or drift) to which they may have been subsequently carried. The Thanet sands are very constant in character from the Isle of Thanet throughout the London basin, but thin out to the westward, till a little north of Windsor they are only 4 feet thick, shortly beyond which they disappear entirely. (Prestwich, Geol. Jour., 1852, p. 235.)

2. The Plastic Clay, or the Woolwich and Reading series of Prestwich.—This group is more variable in character than that of the Thanet sands, and also more widely extended, becoming thicker from east to west, or in the opposite direction to the Thanet sands.

On the east, near Herne Bay, we have in it—

At Black Heath it consists of—

In Alum Bay, Isle of Wight, these beds are from 90 to 140 feet thick, consisting of bright-coloured tenacious mottled clays, the prevailing colour being blood-red, but having mixtures of light bluish-gray and yellow, light and dark slate colour, lavender, puce, yellow, and brown, almost free from any admixture of sand. (Prestwich, Geol. Jour., 1854, vol. x., p. 75.)

The Druid Sandstones, Gray Weathers, Sarsenstones, and Puddingstones, scattered in loose blocks over many of the Chalk downs around the London basin, are believed by Mr Prestwick to be consolidated portions of the sands and gravels of the Plastic clay series.

3. The London Clay.—In the London basin this consists of—

In the Hampshire basin we have—

The Middle Eocene Groups.

4. The Bagshot series, which takes its name from Bagshot Heath, but is best seen in the Isle of Wight. These consist of four groups, namely:—

4a. The Lower Bagshot beds, composed of alternations of sand and clay; the beds generally pale yellow or gray, but sometimes blue, and ferruginous in others fawn-coloured or rose-coloured; the clay are white pipe-clay, or gray or chocolate-coloured clay. Thickness, 660 feet.

4b. The Bracklesham beds (so called from Bracklesham in Sussex).—Dark chocolate-coloured marls and carbonaceous clays below, over which are whitish marly clay and white sands capped by a band of conglomerate of flint pebbles. Thickness, 110 feet.

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1 The total thickness of the fluvi-marine strata of the Isle of Wight, reckoning from the base of the Headon series, will be about 540 feet.

I have given these beds in a little more detail than their relative importance deserves, as a good example of the variable character of some of the Tertiary beds of Western Europe. The Barton beds.—Greenish-gray sandy clay below, passing up into bluish green and brown clay; interstratified occasionally with beds of sand and loam. Thickness, 300 feet. This was formerly supposed to be the London clay.

4 d. Upper Bagshot beds.—Yellow and white sands with ferruginous stains. Occasionally 120 feet.

(Mr Bristow's section in Mem. Geol. Survey, 1856; Forbes' Isle of Wight Mem.)

The arrangement is different from that given by Mr Prestwich in his papers in the Geological Journal. It appears that No. 16 of Mr Bristow's section, p. 157, is the same as No. 24 of Mr Prestwich's in Geological Journal, vol. ii., p. 258. All below that Mr Bristow called Lower Bagshot, while Mr Prestwich includes many of the sands below in his Bracklesham series. (Geological Journal, vol. xiii., p. 99.)

5. The Headon series.—All the beds hitherto described, except part of the Plastic Clay series, are of marine origin. With the commencement of the Headon series, however, we meet with indications of fresh water having prevailed over what is now the Hampshire area, as well as at the corresponding period of the Paris Tertiaries. In the London area no beds higher than the Bagshots are known.

5 a. The Lower Headon beds consist of clays and marls in Whitecliff Bay, while at Headon Hill and Colwell Bay they contain thick limestones; and they are still more varied at Hordwell on the opposite coast. They are the "Lower Fresh-water formation" of Webster.

5 b. The Middle Headon beds consist principally of sands, showing at Headon Hill brackish water conditions, but containing beds of oysters; while at Colwell Bay and Hordwell, and still more strongly at Whitecliff Bay, the beds have a purely marine character. Webster called them the "Upper Marine formation."

5 c. The Upper Headon beds contain the strongest limestones of Headon Hill, which, however, thin out rapidly towards the north. They are represented by a few very thin and inconspicuous sandy concretionary bands in Whitecliff Bay. The uppermost beds of the group are marls. Webster gave the name of "Upper Fresh-water formation" to this group.

6. Osborne (or St Helen's) series.—This is divisible into two groups, of which the first or lowest is—

6 a. The Nettlestone grits, consisting of hard rag and shelly sandstone below, capped by marl and bright-yellow limestone. The whole about 20 feet in thickness.

6 b. The uppermost has an alternation of white, and green, and yellow sands, with blue, white, and yellowish clays and marls, having a total thickness of about 50 feet.

The Upper Eocene Groups.

The fluvi-marine conditions are still continued in the Isle of Wight district, without any very marked line of distinction, between the top of the middle and the base of the Upper Eocene groups.

7. The Bembridge series, of which the first or lowest division is—

7 a. The Bembridge limestone, a pale yellow or cream-coloured limestone, interstratified with clay or crumbling marl—the limestone full of cavities, and often quite tufaceous and concretionary, and sometimes conglomeritic, sometimes a true travertine; contains siliceous or cherty bands in some places. Thickness, 20 to 23 feet.

7 b. The Thanet Beds, a few feet of greenish sands containing oysters (Ostrea Fucensis) in great abundance, capped by a band of hard septarian stone, which is constant over a large area. About 10 feet in thickness.

7 c. Unfossiliferous mottled clays, alternating with fossiliferous laminated clays and marls. Containing Cyrena pulchra.

7 d. Marls and laminated gray clays, containing Melanoid territilis; capped by the Black Band forming the base of the Hempstead series.

8. The Hempstead series—the three lower divisions of fresh-water and estuary origin.

8 a. The lowest bed of this group is a firm carbonaceous laminated clay, highly fossiliferous, about two feet thick, known as the Black Band, over which are pale-bluish and yellow shaly marls, with ironstone concretions. The whole about 40 feet thick.

8 b. The base of this group, called the White Band, is a bed of mingled broken and entire shells, more or less consolidated, often very ferruginous, from 6 inches to 2 feet thick; over which are mottled, yellow, and pale-green marls, capped by shaly clays and dark marls, and blue-green ferruginous clays, with ironstone concretions. Total thickness about 50 feet.

8 c. Variegated red and green marls and gray clays, covered by greenish clay, passing up into pale and dark gray or lead-coloured clays. Thickness about 40 feet.

8 d. Clays with septaria, and gray and bluish clays with concretions containing abundance of Corbula; marine. About 25 feet thick.

France and Belgium.—The labours of Mr Prestwich, continued so long and assiduously, have gradually made plain to us the correlation of the English and French Eocene beds, and joined with those of Sir C. Lyell and M. Dumont, have also taught us the relation of these with those of Belgium. The following table exhibits these relations as they are now believed to be, taking Mr Prestwich's classification for all below the Upper Bagshot sands, and Professor Edward Forbes' for these and all above them:

| England | Belgium | France | |---------|---------|--------| | 11. Hempstead. | Rupellen. | Calcaire de la Beauce. | | 10. Bembridge. | Tongrien. | Grès de Fontainebleau. | | 9. Osborne. | Laekenien, part of? | Sables et bancs de coquilles, marines marines. | | 7. Upper Bagshot. | Système Laekenien supérieur? | Calcaire alluieux, calcaire lacustre moyenne, Gypso-sous series of Montmartre, &c. | | 6. Barton clay. | Système Laekenien inférieur. | Calcaire marin et Grès de Beauchamp. | | 5. Bracklesham. | Système Bruxellien. | Sables moyennes, upper zone. | | 4. Lower Bagshot. | Système Ypresien supérieur? | Sables moyennes, lower zone. | | 3. London clay. | Système Ypresien inférieur? | Calcaire grossier, and Glacconie grossière. | | 2. Woolwich and Reading. | Système Landenien supérieur. | Lits coquillères, and Glacconie moyenne. | | 1. Thanet sands. | Système Landenien inférieur. | Wantling. |

According to Mr Prestwich, the London Tertiaries were

1 Mr Prestwich gives (Geol. Jour., vol. xiii., p. 99) the following detailed description of the Calcaire grossier:—

Feet. 4. Compact white marls, passing down into alternations of greenish marls and thin yellow limestones, with seams of chert... 20 3. Thin-bedded fissile calcareous flags and sandstones, alternating with white marls and limestones... 15 2. Thick mass of soft, light yellow calcareous freestone (the famous stone of Paris got by mining or subterranean quarrying), passing somewhat into calcareous sands... 40 1. Variegated, more or less calcareous greenbands, sometimes concreted, flint pebbles often at base... 25

Some part of it, however, formerly extended into Normandy, as some clay at the top of the cliff of Ally, near Dieppe, is believed to be London clay. (Prestwich, Geol. Jour., vol. xi., p. 230.) Geology: deposited in a sea open to the north, spreading at least over South-East England, Belgium, and north of France, whilst to the south of that area, dry land prevailed over the great part of the Paris Tertiary district and still further south. Gradual depression then took place, extending the limits of the sea over the Paris area, leading to the introduction of Nummulites and more southern forms of marine life than had hitherto prevailed. Dry land was still in the immediate neighbourhood, as shown by the occasional presence of terrestrial forms, and alternations of elevation and depression doubtless took place, modifying here and there the physical geography of the district. The Barton Clay, for instance, seems to have been deposited in a sea of a more northern character than that in which the Bracklesham Clays and sand were formed. Fresh-water conditions finally became prevalent, large estuaries opened into the seas over the British and north of France areas, while large lakes existed in the centre and south of France, where, soon after, volcanic eruptions commenced to break forth, and continued for many thousand years in subsequent periods. Edward Forbes pointed out that the upper part of the Bembridge series was probably of the same age as the Molasse of Fronsadais and the associated beds, and also as the Calcaire à Astéries of the S.W. of France. Part of the Tertiary beds of Malta, Corsica, Greece, Crete, Corigo, S. of Spain and Portugal, Azores, and North Africa, are also believed to be contemporaneous with these beds. Contemporaneous with the Hempstead also were the Molasse ossifère and the Faluns jamez of Dax, the lower division of the Vienna Tertiaries; and the marine beds, the Cerithium kalk and Upper Brown Coal of Mayence. (Mems. Geol. Soc. 1856, p. 100.)

Sir C. Lyell, however, in his Supplement, thinks that it would be more convenient to retain a nomenclature common on the Continent, and to class the Hempstead series and its contemporaneous beds as Lower Miocene, taking the beds from the Barton Clay to the Bembridge series inclusive as Upper Eocene, and the Bracklesham and Lower Bagshot beds only as Middle Eocene. He remarks, however, that we must in this case look on the boundary between Eocene and Miocene as an arbitrary and purely conventional line.

Certainly, as far as England (Isle of Wight) is concerned, the Hempstead beds are linked to those below by a greater number of species than they have peculiar to themselves.

The Alps, the Borders of the Mediterranean, Egypt, India.—Through these countries, from the Alps to the Himalayas, occurring at intervals through 25° of latitude and near 100° of longitude, are found great masses of rock, sometimes even thousands of feet in thickness, crowded with Nummulites, and sometimes almost made up of them. These are of Middle Eocene age. Associated with these are still higher beds called Flysch and Macigno in the north of Italy, and the black slates or shales of Glarus containing quantities of fossil fish, &c. The Monte Bolca fish-beds are also of about this age. (Murchison, Geol. Jour., vol. v., p. 157, &c.)

North America.—Sir C. Lyell places the Claiborne and Alabama beds among the productions of the Middle Eocene period.

THE MIOCENE PERIOD.

The proportion of living to extinct species is taken at about 25 per cent. If we include the Hempstead series in the deposits of the Eocene period, we have no stratified rocks in the British Islands representative of the formations of the Miocene period, unless it be the "ash" beds and lignites associated with the basalt of the north of Ireland and west of Scotland. Edward Forbes thought that the fossil leaves found by the Duke of Argyll in the Isle of Mull more nearly resembled Miocene forms than any other, and were certainly not the same with those of any known Eocene forms.

If we adopt the classification usual on the Continent, and consider the Hempstead beds and their equivalents the earliest of Miocene beds, then the Bembridge series of the Isle of Wight, and the Gypseous series of Montmartre, will be the uppermost or newest of the Eocene period. There is, it appears, a palaeontological reason for this arrangement on the Continent, inasmuch as if we draw the line at the top of the Montmartre beds, and at the base of the Calcaire lacustre superior (or Calcaire de la Beauce), certain generic and even specific forms of Mammalia are kept wholly within the Miocene groups which otherwise would be made common to the Eocene and Miocene periods. The genera Dorcatherium, Cainotherium, Anchietherium, and Titanomys, and the species Rhinoceros incisivus, and others, are examples. (M. Lartet, in Lyell's Supplement.)

We shall then have the following as

Typical Groups of Rocks of the Miocene Period.

—Belgium and France.—Limburg beds, Rupelian of Du mont, the Bolderberg beds, the Fuhns of Touraine and Bordeaux, the principal part of the lacustrine strata of Auvergne and Central France. Associated with the latter were the earliest beds of lava and volcanic breccias, which began now to be poured forth in the districts of Auvergne, Velay, and Cantal, and continued to break forth at intervals to far later times.

Germany and Switzerland.—The Mayence basin, the principal part of the Vienna basin, part of the Molasse of Switzerland, containing the "nagel-flue," a conglomerate 6000 or 8000 feet thick.

Italy.—Part of the beds in the hill of Superga, near Turin.

North America.—The sands of Richmond, and the James River in Virginia.

India.—The Sewalki formations, which compose the sub-Himalayan range of hills. (Lyell's Manual.)

PLIOCENE PERIOD.

Typical Groups of Rocks.

| Rock Type | Feet | |--------------------|------| | Red Crag | 50 | | Coralline Crag | 40 |

1. The Coralline Crag is composed chiefly of soft marly sands of a white colour, sometimes speckled with green, containing occasionally thin bands of flaggy limestone. It is generally about 20 feet, but sometimes as much as 50 feet in thickness. Near Ipswich it has been denuded, and the Red Crag is seen to lie in the hollows that have been eroded in it, which is the only direct evidence of the superposition of the Red Crag on the Coralline; otherwise they lie side by side, the Coralline Crag being confined to a strip of country 20 miles long by 3 or 4 wide, stretching through Ipswich from the Stour River to the Alde River.

2. The Red Crag consists of beds of red quartzose sands and gravel, with accumulations of rolled shells. It is very variable in character, sometimes regularly stratified, sometimes more confused.

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1 It is, however, most probable that the great volcanoes of the Most Dor and the Cantal, &c., are of a still earlier period, as may be surmised from their more ruined and eroded character, the obliteration of their craters, and the great valleys worn deep into the flanks of their wide-spread mounds.

2 It appears that this term of Coralline is a mistake, inasmuch as true corals are rare in both the divisions of Crag, while the coral-like bodies which are common in the Lower Crag are Polyzoa, and are also found, though not so abundantly, in the Red Crag. (Edward and Haime, Palaeontographology, vol. I.) Both groups resemble the deposits which we may now suppose to be taking place in the shallow bed of the German Ocean.

Antwerp.—Sir C. Lyell (Manual, p. 174) describes strata around Antwerp, and on the banks of the Scheldt below that city, containing 200 species of shells, of which two-thirds are the same as those of the Crag of Suffolk. More than half are living species, principally belonging to the Celtic, though containing some Lusitanian (Mediterranean) species.

Normandy.—The same authority mentions a patch of Crag near Valognes in Normandy, and at other places, extending to a little south of Carentace, but none farther.

Italy.—The sub-Appennines or low hills intervening between the Appennines and the sea, on each side of Italy, are made of Tertiary strata, of which part are of Miocene, part of Pliocene, and part of a still more recent period. The beds of Asti and Parma, and the blue marl of Sienna, which near Parma is 2000 feet thick, over which are yellow sands and conglomerates formed on the shallowing of the sea, belong to this period, as do the Tertiary marine beds forming the base of the seven hills of Rome.

South Russia.—Sir R. Murchison and M. de Verneuil describe limestone and sands, rising occasionally to the height of several hundred feet above the sea around the coasts of the Caspian and Aral Seas, and the north-western parts of the Black Sea, as belonging to this period. They call them the Aralo-Caspian formation. The fossils are partly fresh-water, partly marine.

PLEISTOCENE PERIOD.

Without attempting to draw any very nice or accurate distinction between the deposits of this and the preceding period, we may take, as a rough definition of the Pleistocene deposits, "those in which more than three-fourths of the fossils are of existing species."

We know of no remarkable living generic forms, with the exception only of man, that may not have been in existence during this period. The horse, the ox, the dog, and all the variety of terrestrial Mammalia, seem now to have been disseminated over the earth, each species in its own province, very much as they are now distributed. The species of Mammalia were almost always, and in some cases even the genera were, different from those now occupying the province, while the species of Mollusca, &c., were nearly the same.

Typical Groups of Rocks.—Britain.—The assemblage of sands and gravels about the county of Norfolk, known as the Mammiferous or Norfolk Crag, containing both marine and fresh-water shells, and the bones of mammoths, together with those of the horse, dog, pig, deer, &c.,—deposits of Brentford (Middlesex), of Gray's (Essex), and of Maidstone (Kent), containing the bones of the mammoth or woolly elephant (Elephas primigenius); the extinct woolly rhinoceros (Rhinoceros tichorhinus), a monkey (Macacus plioceenus), and fresh-water shells, which, though not extinct entirely, are no longer inhabitants of Britain; one of them, for instance (Cyrena consobrina), being now only found in the Nile; the elephant bed near Happisburgh (Norfolk), underlying "the drift" there, and stretching under the sea, from which, according to Woodward, 2000 mammoths' grinders were dredged up by the fishermen in thirteen years; the clay deposit at Chillesford, Suffolk, described by Prestwich. (Jour. Geol. Soc., vol. v., p. 345.)

Other similar partial superficial patches of clays, sands, and gravels, some of the gravels being widely spread over high ground, and known as the "high-level gravels," having the present river valleys excavated through them, others occupying these valleys and the lower grounds, and known as the "low-level" gravels. Some of these deposits are older, and some newer than the Glacial beds to be mentioned presently.

It was about this time, perhaps, unless it were still later after the close of the Glacial period, that the caves of the British Islands were inhabited by large hyenas and bears (Hyæna spelæus and Ursus spelæus and præsæ). Into these dens many bones of other animals then inhabiting the neighbourhood were dragged by them. These remains are generally found in mud, under a layer of stalagmite.

The Glacial Deposits are chiefly clays, sands, and gravels, sometimes stratified, sometimes rudely piled together, and containing great blocks of rock, which also sometimes occur scattered loosely over the surface. They are variously called by the terms of "Great Northern Drift," "Till" (in Scotland), a brown clay with boulders; "Marls" in Wexford and Wicklow, where fossiliferous marl is interstratified with sand and gravel; "Limestone Gravel" in Central Ireland, chiefly consisting of pebbles of Carboniferous limestone, heaped sometimes into narrow ridges 40 or 50 feet high, and from 1 to 20 miles long, which are called "Escars;" "the Boulder Clay" in Northern and Central England, &c.; and "Drift" almost universally. The "Erratic Block group" of Delabecque is likewise a well-known name for these deposits.

The fossils of the Coralline Crag have a southern, while those of the Red Crag have a more northern aspect; those which are found at Gray's, &c., still point to a climate more like that of the south of Europe than our own, though as far as the woolly elephant and woolly rhinoceros are concerned, they might well have inhabited Britain at the present day, or even countries with a still severer climate.

A change, however, now took place, of a kind different from any we have yet met with, unless Professor Ramsay's ideas as to the glacial origin of the Permian and other old conglomerates be well founded. Simultaneously with a gradual, but eventually a great and wide-spread, depression of land, amounting in many places to 2000 or 2500 feet, there was a refrigeration of the climate of our own latitudes, so that the glees of our present mountains were encumbered with glaciers, even where their valleys were penetrated by the sea, and our low lands were entirely submerged. By the action of these glaciers, the rocks were scored and rounded, polished and grooved, and masses of rock carried down and heaped into moraines, while great blocks of rock were transported on fragments of those glaciers which dipped into the sea, and formed icebergs, being often carried far over the shallow seas, and dropped many miles from their parent sites, sometimes resting on hill-tops, which were then banks and shallows in the sea, and so arrested the icebergs in their course. Alternations of elevation and depression doubtless took place, and the ordinary action of the breakers along the beach was aided by the quantity of detritus poured into it by the glaciers, and modified by that of the shore ice which formed along it in the winter seasons.

The Escars of Ireland were probably formed in the eddies at the margins of opposing and conflicting currents, the materials being piled up from each side.

These Glacial deposits are not confined to the British Islands, but extend over all the north of Europe and North America, down to a certain curved boundary, which in

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1 The largest boulder I know in the British Islands is near the head of the Devil's Glen in county Wicklow. It is 27 feet long, by 18 wide, and 15 high. It is of granite, resting on Cambrian grits and slates, six or eight miles from the nearest granite islet, with a wide shallow valley between the hill on which it now stands and the granite district. At the recent meeting of the British Association at Dublin, Mr Godwin Austen described a large boulder of granite (apparently Scandinavian) found in the chalk near Croydon, showing that occasional icebergs wandered southwards even in the Cretaceous period. Geology. Europe, according to Sir R. I. Murchison, only stretches so far S. as Lat. 50° in one part of its course, namely, near Cracow. Great blocks of Swedish or Norwegian rocks, as large as cottages, lie scattered over the plains of North Germany.

Towards the close of the Glacial period, or after it, our present low lands seem to have been again above water, and to have been more extensive than they now are; the British Islands being probably united to each other, and to the Continent, by plains which have since been widely eroded, and the shallow seas formed out of them that now separate our present lands. On these plains the Irish elk, the reindeer, the musk-ox, and other animals roamed, sometimes becoming drowned in the lakes or mired in the swamps, and leaving their skeletons as records of their former existence.

During the prevalence of the cold climate of the Glacial period many species of Molluscs which previously inhabited the British seas, and are found fossil in the Crag, retired southwards, and occur fossil in the Mediterranean Pleistocene deposits; but at the close of the Glacial periods they again came northwards, and are now inhabitants of our seas for the second time, while some of them no longer live in the Mediterranean.

Dr Falconer has recently shown that a similar history might be told with respect to the Mammalia. The Elephas primigenius has, according to him, never been found south of the Alps, where an allied species, E. antiquus, has left its remains (Lyell's Supplement); that species having previously roamed much farther north, and left its remains in the earlier Pleistocene deposits of Britain. Mr Godwin Austen informs us that Dr Falconer believes that the relative ages of the different drifts or superficial deposits may ultimately be worked out by paying attention to the different species of elephant found in them. (Austen "On Newer Tertiary Deposits of Sussex Coast,"—Geological Journal, vol. xiii., part i.,—in which Mr Austen now would write E. antiquus for E. primigenius, on p. 50, line 18, and p. 55, line 8 from bottom, on Dr Falconer's authority.)

In like manner the Arctic or Boreal fauna and flora which prevailed over our islands and shores during the Glacial period, have receded towards the north again, but have left some traces of their former existence in the Arctic or Boreal plants which are found near the summits of our mountains, and the Boreal shells which may be dredged from certain deep hollows in our sea. Edward Forbes showed that the present fauna and flora of the British Islands is derived from five sources.

1. The remnant of a Spanish (Lusitanian) flora in the W. of Ireland, probably dating from the Miocene period. 2. A Gallican or Norman flora in the S.W. of England and S.E. of Ireland, with a remnant of a corresponding fauna. 3. A Kentish or north of France flora, and corresponding fauna, extending over the S.E. of England. These two may both perhaps be of Pliocene date. 4. The Arctic flora and fauna just spoken of, diminishing in numbers from the N. of Scotland towards the S. of England. 5. The great Germanic flora and terrestrial fauna, occupying all the central and northern parts of England and Ireland and south of Scotland, and spreading through the other districts in co-tenancy with the rest, dating from the time when the British Islands were united by the great plain to each other and the Continent.

The Celtic marine fauna comes in with this; its peculiar species being apparently created to occupy the shallow seas formed by the erosion of this great plain, and inhabiting them together with the Arctic or Boreal species that remained about the coasts and spread into the new sea, and such of the southern species as returned to it from the Lusitanian province. One or two Arctic or Boreal outliers occur in deep cold hollows of the British seas, containing species not found elsewhere till we go much farther north, just in the same way that the tops of our loftiest mountains have plants not found on our lower grounds and plains, but occurring down to the waters' edge in Scandinavia.

It appears that just as the present surface of all land is formed by the outcrop of a number of beds of different ages, the newest being generally the most widely spread, and concealing the others, except in some particular localities where they rise up to view; so the population of animals and plants—the fauna and flora—of many countries, may be made up of different assemblages of different dates and different origins,—the newest perhaps spreading over, and more or less concealing, the others, the oldest only perhaps becoming apparent in one or two separated and isolated localities.

Besides the "Great Northern Drift," consisting of far-travelled boulders and fragments, there is also a much more generally diffused local drift, the materials of which are always derived from the immediate neighbourhood. This may be either contemporaneous with, or of earlier or later date than, the Glacial period, but is most probably later, and much of it perhaps of subaerial origin. It is occasionally of very considerable thickness and importance in the British Islands, and similar "drifts" are found in other parts of the world in all latitudes, and not confined, like that of the Glacial period, to high northern or southern regions.

Raised Beaches and Submarine Forests.—Neither is our history brought to a close after the formation of all our present deposits, and the coming into existence of all our present species. Changes of level have since taken place, as shown by the occurrence of raised beaches, in the shape of banks of sand and shingle with shells, above high-water mark, round our coasts, containing just such species as occur in the beaches below them; and in the fact of peat bogs, containing the stumps and roots of oak, and fir, and other common trees, to be seen at dead low water, passing under the sea. In many of the bays along the south coast of Ireland peat is dug from such situations at low water of spring tides, and dried and used as fuel.

These facts show us that some of our peat bogs, at all events, may date back from a considerable antiquity. Beds of peat, indeed, sometimes occur beneath the clay and gravel of the Glacial deposits, or interstratified with such deposits.

Soil and Subsoil, Vegetable Mould, &c.—As long as the geologist is engaged only with the local facts, as to the formation of regularly stratified rocks or of large masses of earthy matter, whether regularly or irregularly accumulated, he proceeds with pretty confident steps towards his conclusions. Those conclusions are general ones, and often of a sufficiently sweeping character. Certain districts, now high dry land, were formerly deep sea, in which certain beds were deposited, including the remains of creatures that lived in the sea. The time when these things took place was a very remote one, and the interval occupied by them a long one,—hundreds, thousands, or millions of years, as the case may be. We are not compelled to be more definite, nor have we any inducement to be so. In proportion, however, as we approach the recent or human period, our steps necessarily become more cautious, since we have more of a personal interest in ascertaining precisely the nature of the processes and the period of their occurrence.

We are naturally anxious to know, if possible, the actual date, in years, of the last elevation of the lands we inhabit out of the sea in which they have been so often immersed, and what has taken place upon them between that last emergence and the historic times. Indications, then, which would be at other times overlooked, become now of importance; but in proportion to the interest attached to the investigation becomes its difficulty, since observations now are required to be more accurate and minute, as well as more widely spread, and more strictly checked and compared, than when larger generalities are dealt with. Hence it arises that we have not yet arrived at any satisfactory union of the history of the pre-human and the human periods, and possibly no very satisfactory union may ever be arrived at.

One strictly geological subject has yet scarcely been commenced upon, and that is the formation of soil. The natural formation of soil is certainly not always a rapid one. On many coral islets, crowded with birds and covered with vegetation, some even having considerable trees, there is little that could be called soil. The loose coral fragments and coral sand are slightly discoloured, and from their interstices small particles of "mould" could be picked up with the finger and thumb, but there is no layer of pure soil. Neither does soil always follow vegetation, however long continued. The great gum-tree forests of Australia rise from wide tracts of bare ironstone gravel or bare sandstone rock, slightly covered with an inch or two of rubble, without anything that could be called soil for scores of miles at a stretch. The ground looks like a great untidy gravel walk, from which a few straggling blades of grass spring up here and there between the trees. Neither are even calcareous rocks always covered with vegetation. In Galway and Mayo considerable flats of low ground may sometimes be seen formed of horizontal sheets of Carboniferous limestone, perfectly bare except in the crevices of the joints, where a short sweet grass springs up. On some of the fine corn land of the Cotswold Hills, too, on the Oolitic limestones, the soil is not half an inch in thickness, and is composed principally of the rubble of the rock below, just such a soil as that of a coral islet would be if ploughed.

On some of the downs of the Carboniferous limestone, as also on Chalk downs, the soil consists of about an inch of close green turf, that may be cut with a knife and peeled off; the rock below in great rolls. I am not aware of any experiments for determining how long such bare spots would require to be reclothed with turf by unassisted nature.

Mr Darwin, in a paper in the Trans. Geol. Soc., vol. v., attributes the formation of "mould" to the digestive action of worms, who swallow finely-divided soil, and eject it after extracting the nutritive matter therefrom, and thus improve the nature of the soil.

Foreign Pleistocene Deposits.

It has been said that, during the Glacial period, many of the Molluscs which previously inhabited the British seas retired southwards, and that their remains are to be found fossil in the Pleistocene deposits of the Mediterranean, while they do not now live on that sea, but have returned to their original province. In Sicily, especially, there are two if not more groups of rock, the Lower argillaceous and the Upper calcareous, consisting of thick beds of hard limestone, having an aggregate thickness of 700 or 800 feet. These beds cover half the island, and rise to a height of 3000 feet, the lower portions having as much as 30 per cent. of extinct species, while the upper parts contain shells mostly identical with species now living in the Mediterranean. (Lyell's Manual, chap. xii.) Some of these beds appear to be interstratified with lavas, part of the early outflows of the volcanic focus of Etna.

These thick deposits, which are found in Sicily and the Grecian Archipelago, and some of which may exist in Spain and Portugal, were shown by Edward Forbes to be the contemporaries of the Glacial deposits, or northern "drift" of the higher latitudes, by the evidences already described.

It is perhaps to a later part of this period that we must assign the formation of the "loess" or "lehm" of the valley of the Rhine and its tributaries. This, as described by Sir C. Lyell in his Manual, p. 122, is a deposit of fine loam, of a yellowish-gray colour, occasionally laminated, but never separated into distinct beds, although it is often 200 or 300 feet thick, and rises occasionally to a height of 1200 feet above the sea. It seems to have been formed in consequence of the gradual depression of the whole country, after it had assumed its present external shape and "mould," and the filling up of a great part of the Rhine valley and its tributaries with matter brought down by the floods of the upper parts of the rivers. These materials being then spread from side to side of the valleys, would again be greatly eroded on the gradual re-elevation of the country, when every stream would cut down through the soft loess and re-occupy its old bed. Land and fresh-water shells of the same species that now inhabit the country are found in the loess; and in some places near the extinct volcanoes layers of pumice and lapilli are found, seeming at first sight as if ejected during an eruption, but perhaps merely washed away from the old previously existing cones. One crater, indeed,—that of the Roderberg, near Bonn,—is partly filled by the loess. Bones of the mammoth and other contemporaneous mammals have been found in it.

A similar deposit is described by Sir C. Lyell as found in the valley of the Mississippi, and forming the cliffs called the "Bluffs," which often rise to a height of 200 feet above the present alluvial plain of the river.

It is also to the Pleistocene period that we must assign the deposits of clay and sand which spread over the plains called the Pampas in South America, in which the bones of the Megatherium, Mylodon, and Glyptodon have been found. Similar superficial deposits are found in most countries; and either in these or in the bottoms of caverns, mostly buried under stalagmite, are found more or less of the remains of the extinct animals that preceded the existing races in their occupation of the globe.

There are two remarkable agencies now at work in various parts of the world which are probably more or less intimately connected with the period we are now considering, or perhaps with still earlier periods. Many of our present coral reefs, and many of our active volcanic mountains are of an incalculable antiquity, if we measure them by mere years or centuries, and not by geological periods.

Coral Reefs.—In a former part of this article these most singular, and at first sight most mysterious phenomena, were alluded to as illustrations of the method of formation of marine Calcareous rocks. Mr Darwin, however, has shown them to be also proofs of movements in the crust of the earth, and of great depression having taken place in the bed of the ocean where they prevail. He showed that since reef-making corals could not live at a greater depth than 15 or 20 fathoms (Forbes' Circumtoral Zone), and since vast reefs (Atolls and Barriers) now rise with steep wall-like sides from profound depths in the great Pacific and Indian Oceans, just to the level of low water, their existence is only to be accounted for on the supposition, that when these reefs commenced to grow, the water was shallow enough for the animals to live in it near enough to the surface to enjoy that amount of light, heat, and play of the waves which is necessary for their existence. After the reef was thus commenced and built up to the level of low water (but how long after we cannot say), a slow and gradual motion of depression must have set in, either gentle and continuous, or acting by little fits and starts, never producing during any interval of time an amount of depression so great as to prevent the polyps continuing to raise the reef towards the surface, by the growth and multiplication of the calcareous framework of their own bodies. In this way the ocean bed that was once only fifty or sixty feet, is now hundreds and thousands of feet below the sea-level; and vast masses of calcareous rock are thus erected, as distant barriers encircling islands, some of whose loftiest summits still rise above the water, or as great massive tombs utterly enveloping and burying in their secret recesses the bodies of lands and islands, once rising high into the air, and now lying enveloped in coral rock deep beneath the sea.

It may well be that in some, if not many, of these instances the first movement took place in Pleistocene, Pliocene, or still earlier periods: it is possible even that some of these enormous submarine masses of coral limestone may be based upon corals of species different from those that form their summits—species that have died out in the lapse of time.

Volcanoes.—When we study the structure of a volcanic district such as Etna, Teneriffe, and many others, and find that the lower parts of the volcanic rocks that are open to our observation are interstratified with marine limestones, or sandstones full of sea-shells, we perceive at once that great changes have taken place in the district since the first commencement of volcanic activity. In many instances, such as in the Andes, in Java (see Horsburgh's Map), and perhaps, if they were worked out, in every large volcanic district now at work upon the globe, we are enabled to trace back this commencement of volcanic action to some Tertiary, sometimes, perhaps, to a rather early Tertiary period. One other result which we should arrive at is, that volcanic districts are, as pointed out by Darwin in his volume on Coral Reefs, districts of elevation, and that these in some parts of the world alternate with the districts of depression occupied by coral reefs. Volcanic districts never have atolls and barrier reefs in them.

But even if we dismiss from consideration all the aqueous rocks with which volcanoes are connected, and look solely at the igneous products themselves, we are in most instances compelled to assign an age to the volcano far greater than that of the human race.

Even so small an example as Etna forms, compared with the gigantic volcanoes of Asia and America, will enable us to prove this. This mountain has a base of some 30 miles in diameter, and a height of about 11,000 feet. It has been built up by the ejection of ashes, dust, lapilli, and other fragmentary matter from the interior of the earth, and an occasional outpouring of streams of molten rock. It is made up of an indefinite number of conical heaps of such materials, arranged variously around one central and dominant mound, from which the greatest quantity of matter has been ejected. Some of these external cones are fully shown; some are half buried by the ejectamenta from other cones, or from the central one; and many others are doubtless altogether concealed under the great piles of materials heaped over the central parts of the mountain. On one side a huge ravine, 3000 feet deep and 5 miles long, has either been scooped out of the mountain by erosion or formed by subsidence.

Now the sensible additions made to this great mass of materials during the last 2000 or 2500 years bear a very trifling and insignificant proportion to the whole mass; and yet nothing we know of the structure of Etna, or of volcanic action in any other parts of the globe, warrant us in concluding that it has been built up by a process much more rapid in its action than the one that has been going on during the last 2500 years. Even if we make allowance for a considerably more energetic action during the earliest periods of its activity (which, however, nothing that we know of volcanic action would compel us to do), and suppose that it did not assume its present slow rate of growth till it became as large as Vesuvius, for instance, still the additional matter added to the bulk of Etna since it attained that size must be so great that, judging from our experience of the rate of volcanic action all over the world, we could not allow a less period than one or two hundred thousand years for the process.

The mention, however, of such a period as a hundred thousand years is only introduced here to show the long period of time necessary; a million may have been nearer the truth for all anybody can show to the contrary; and if once even so much as 20,000 or 30,000 years be allowed as possible, no one would, I suppose, be inclined to insist upon further limitation from any considerations relative to human history.

But if such conclusions may fairly be drawn from the consideration of the structure of the comparatively small hill of Etna, what period of time are we to allow for the slow and gradual piling up of the lofty cones of Chimborazo, Cotopaxi, Aconcagua, and others of the Andes, rising to twice the height of Etna, spreading their bases over a width equal to the whole island of Sicily, and running through hundreds and even thousands of miles in length. We cannot conceive all the vast chain of the Andes ever to have had all its fiery vents in fierce activity at once. We know that in all volcanic chains eruptions take place successively, now from one, now from another; their very number therefore increases the time we must allow for the gradual accumulation of each, especially when we have to intercalate vast periods, during which they may have been all quiescent together. And yet these are most recent geological events; their operation is most obviously continued into our own times, and directly link our own history with the far receding past.

These are not unnecessary or superfluous speculations, but considerations requisite to enable us the better to understand and appreciate the geological facts of our own islands. When we see that hundreds of thousands, or even millions, of years have probably elapsed, during which other countries have stood pretty much as we now see them, except that the grand monuments that rise from them have been slowly elaborated, we can make proper allowance for the great spaces of time which have elapsed during the process of the comparatively insignificant changes that have taken place in our own lands. We learn to look upon the Glacial period, for instance, as separated from our own days by the lapse probably of millions of years, and we begin to understand how it is that physical causes, acting with infinitesimal slowness, have so changed the climate and the physical geography of our own part of the world, as to have caused the gradual extinction of whole races of large animals that once flourished in it.

Large, indeed, as the demands of the geologist may have been thought upon the bank of time, they probably fall far short of the capital stored up there for his future use. Some of the more recent of geological events are probably in reality of an antiquity as great as we have been accustomed to assign in our imaginations to the most remote. The Pleistocene period is probably really as far separated from us in past time as we have hitherto been accustomed to consider the Silurian or Cambrian periods removed from us. Geologists themselves have perhaps hardly formed adequate conceptions on this subject; and yet without those conceptions, difficulties are perpetually rising in the science which with them would disappear.

(J.B.J.)