(from bofai, "iron," or barani, Name, de-diligenter examino), in Natural History, a heavy, hard, vitrified stone, chiefly black or green, consisting of prismatic &c. crystals, the number of whose sides is uncertain. The English miners call it coke; the German schloerl. Its specific gravity is to that of water as 3000 or upwards to 1000. It frequently contains iron; and consists either of particles of an indeterminate figure, or of a sparry, flinted, or fibrous texture. It has a flinty hardness, is insoluble by acids, and is fusible by fire. BAS

The following is an analysis of some basaltes by Mr Bergman; and as the resemblance of it to lava will be frequently mentioned in the succeeding part of this article, we shall here contrast this analysis with that of lava by the same author.

Comparative analysis of basaltes and lava.

<table> <tr> <th>Basaltes, 100 parts contains</th> <th>Lava, 100 parts contains</th> </tr> <tr> <td>Siliceous earth 50</td> <td>Siliceous earth 49</td> </tr> <tr> <td>Argillaceous 15</td> <td>Argillaceous 35</td> </tr> <tr> <td>Calcareous 8</td> <td>Calcareous 4</td> </tr> <tr> <td>Magnesia 2</td> <td>Iron 12</td> </tr> <tr> <td>Iron 25</td> <td></td> </tr> </table>

Phil. Tran. Edin. vol.v.

Dr Kennedy, an ingenious chemist, analyzed several species of basalt, whinstone, and lava, of which the following are the results.

Basalt from Staffa contains, in 100 parts,

<table> <tr> <th>Silex</th> <th>48</th> </tr> <tr> <th>Argil</th> <th>16</th> </tr> <tr> <th>Oxyd of iron</th> <th>16</th> </tr> <tr> <th>Lime</th> <th>9</th> </tr> <tr> <th>Moisture and other volatile matter</th> <th>5</th> </tr> <tr> <th>Soda, about</th> <th>4</th> </tr> <tr> <th>Muriatic acid, about</th> <th>1</th> </tr> </table> 99

Whinstone of Salisbury rock near Edinburgh contains, in 100 parts,

<table> <tr> <th>Silex</th> <th>46</th> </tr> <tr> <th>Argil</th> <th>19</th> </tr> <tr> <th>Oxyd of iron</th> <th>17</th> </tr> <tr> <th>Lime</th> <th>8</th> </tr> <tr> <th>Moisture and other volatile matter</th> <th>4</th> </tr> <tr> <th>Soda, about</th> <th>3.5</th> </tr> <tr> <th>Muriatic acid, about</th> <th>1</th> </tr> </table> 98.5

Whinstone from Caltonhill near Edinburgh contains, in 100 parts,

<table> <tr> <th>Silex</th> <th>50</th> </tr> <tr> <th>Argil</th> <th>18.5</th> </tr> <tr> <th>Oxyd of iron</th> <th>16.75</th> </tr> <tr> <th>Carbonate of lime</th> <th>3</th> </tr> <tr> <th>Moisture and other volatile matter</th> <th>5</th> </tr> <tr> <th>Soda, about</th> <th>4</th> </tr> <tr> <th>Muriatic acid, about</th> <th>1</th> </tr> </table> 98.25

Lava from Catania, Mount Ætna, contains in 100 parts,

<table> <tr> <th>Silex</th> <th>51</th> </tr> <tr> <th>Argil</th> <th>19</th> </tr> <tr> <th>Oxyd of iron</th> <th>14.5</th> </tr> <tr> <th>Lime</th> <th>9.5</th> </tr> <tr> <th>Soda, about</th> <th>4</th> </tr> <tr> <th>Muriatic acid, about</th> <th>1</th> </tr> </table> 99

BAS

Lava from Sta Venere, Ætna, contains in 100 parts, Basaltes.

<table> <tr> <th>Silex</th> <th>50.75</th> </tr> <tr> <th>Argil</th> <th>17.5</th> </tr> <tr> <th>Oxyd of iron</th> <th>14.25</th> </tr> <tr> <th>Lime</th> <th>10</th> </tr> <tr> <th>Soda, about</th> <th>4</th> </tr> <tr> <th>Muriatic acid, about</th> <th>1</th> </tr> </table> 97.5

The most remarkable property of this substance is its figure, being never found in strata, like other marbles, but always standing up in the form of regular angular columns, composed of a number of joints, one placed upon, and nicely fitted to another, as if formed by the hands of a skilful workman. See Plate LXXXV. fig. 15.

Basaltes was originally found in columns in Ethio-Basaltes, pia, and fragments of it in the river Tmolus, and where some other places. We now have it frequently, both in columns and small pieces, in Spain, Russia, Poland, near Dresden, and in Silecia; but the noblest store in the world seems to be that called the Giant's Causeway in Ireland, and Staffa, one of the western isles of Scotland *. Great quantities of basaltes are likewise * See found in the neighbourhood of Mount Ætna in Sicily, Giant's of Hecla in Iceland, and of the volcano in the island Caufeway of Bourbon. These are the only three active volcanoes in whose neighbourhood it is to be met with; but it is also found in the extinguished volcanoes in Italy, though not in the neighbourhood of Vesuvius.

In Ireland the basaltes rises far up the country, runs Of the into the sea, crosses at the bottom, and rises again on Giant's the opposite land. In Staffa the whole end of the island is supported by natural ranges of pillars, mostly above 50 feet high, standing in natural colonnades, according as the bays and points of land have formed themselves, upon a firm basis of solid unformed rock. Above these, the stratum, which reaches to the soil or surface of the island, varies in thickness, as the island itself is formed into hills or valleys, each hill, which hangs over the valleys below, forming an ample pediment. Some of these, above 60 feet in thickness from the base to the point, are formed by the flopping of the hill on each side, almost into the shape of those used in architecture.

The pillars of the Giant's Causeway have been very particularly described and examined. The most accurate account of them is to be met with in a work entitled, "Letters concerning the northern coast of the county of Antrim;" from which the following particulars relative to the present subject are extracted.

"1. The pillars of the Causeway are small, not very much exceeding 1 foot in breadth and 30 in length; account of sharply defined, neat in their articulation, with concave or convex terminations to each point. In many of the capes and hills they are of a larger size; more plate imperfect and irregular in their figure and articulation, LXXXVI. having often flat terminations to their joints. At fig. 1. Fairhead they are of a gigantic magnitude, sometimes exceeding 5 feet in breadth and 100 in length; oftentimes apparently destitute of joints altogether. Through many parts of the country, this species of stone is entirely rude and unformed, separating in loose blocks; in which state, it resembles the stone known in Sweden by the name of trappe.

"2. The pillars of the Giant's Causeway stand on the level of the beach; from whence they may be traced through all degrees of elevation to the summit of the highest grounds in the neighbourhood.

"3. At the Causeway, and in most other places, they stand perpendicular to the horizon. In some of the capes, and particularly near Ullet harbour, in the isle of Bagherry, they lie in an oblique position. At Doon point in the same island, and along the Balintoy shore, they form a variety of regular curves.

"4. The stone is black, close, and uniform; the varieties of colour are blue, reddish, and gray; and of all kinds of grain, from extreme fineness to the coarse granulated appearance of a stone which resembles imperfect granite, abounding in crystals of schorl, chiefly black, though sometimes of various colours.

"5. Though the stone of the Giant's Causeway be in general compact and homogeneous; yet it is remarkable, that the upper joint of each pillar, where it can be ascertained with any certainty, is always rudely formed and cellular. The grotto pillars also in the capes and mountains frequently abound in these air-holes through all their parts, which sometimes contain fine clay, and other apparently foreign bodies: and the irregular basaltic beginning where the pillars cease, or lying over them, is in general extremely honey-combed; containing in its cells crystals of zeolite, little morules of fine brown clay, sometimes very pure steatite, and in a few instances bits of agate."

Sir Joseph Banks observes, that the bending pillars of Staffa differ considerably from those of the Giant's Causeway. In Staffa they lie down on their sides, each forming the segment of a circle; and in one place, a small mass of them very much resembles the ribs of a ship. Those of the Giant's Causeway which he saw, ran along the face of a high cliff, bent strangely in the middle, as if unable, at their first formation, while in a soft state, to support the mass of incumbent matter.

The rocks of the Cyclops, in the neighbourhood of Mount Etna, exhibit very magnificent basaltic pillars. A general view of them is given on Plate LXXXVI. fig. 2, where a, b, c, are the three principal rocks; e is the extremity of an island, one half of which is composed of lava, on a base of basaltes, of no uncommon nature; above which there is a crust of pozzolana, combined with a certain white calcareous matter, which is pretty hard and compact; and which, as it is composed by the action of the air, appears like a piece of knotty porous wood. That rock, at some former period, became so hard as to split; and the clefts were then filled up with a very hard and porous matter like scoria. This matter afterwards acquiring new hardness, also split, leaving large interstices, which in their turn have been filled up with a species of compound yellow matter. The island was formerly inhabited; and there still remains a flight of steps leading from the shore to the ruins of some houses which appear to have been hewn in the rock.

The rock b has the straightest and most regular columns of any. It is represented distinctly in Plate LXXXVII. fig. 1, and likewise a general view of c and d, with the foot of Etna leading to Catanea.

These basaltic columns, at first view, seem to resemble those of the Giant's Causeway, and others commonly met with: but on a nearer inspection, we find a remarkable difference; being assembled in groups of five or six about one, which serves as their common centre. They are of various sizes and forms; some square, others hexagonal, heptagonal, or octagonal. One half of this rock is composed of perpendicular columns; the other of another species of basaltes disposed in inclined, and almost rectilinear, layers. These are in contact with the columns, and are as closely connected with them as they are with one another. The layers are longer at the base than towards the top of the rock. It is further to be remarked, that most of these layers are subdivided as they rise upwards; so that towards their upper extremities, one layer presents to the eye sometimes one, sometimes two, and sometimes three, divisions. The fragments of basaltes taken off from these layers are of a rhomboidal figure, because the layers break obliquely.

These layers, though inclined towards the base, become almost perpendicular towards the upper part of the rock, where they appear united in a point, and overtop most of the visible and elevated parts of the prismatic columns. These columns terminate in such a manner as to form a kind of stair-case. They appear even to rise under a species of clay with which they are covered at one extremity, till they reunite themselves with the point which is formed by the most elevated parts of the layers of basaltes beside them.

This extraneous matter with which these columns are covered, and of which the summit of this pyramid consists, appears to be of the same species with the former, composing the upper part of the island already described.

The basaltes of that island has one particularity, viz. that it is full of small crystals of about the size of peas. These appear no less beautiful than rock-crystal; but they are much softer, and yield even to the action of the air. We see here large fragments of basaltes which were formerly full of crystals, but destroyed by time. They are now not unlike a sponge, from the great number of holes which appear all over their surface. Those pieces of basaltes which contain most of these crystals are not so hard as those which contain fewer of them.

The promontory of Castel d'Iaci, which terminates the basis of Etna, is almost entirely composed of basaltes, but of a kind very different from the former. It consists of a great number of cylinders, from the diameter of fix inches to that of twenty feet. Some of these are solid, others hollow like cannon: some extended in layers, others similar to carrots of tobacco consisting of a number of pieces squeezed together. Some of these cylinders are straight, others curved into a variety of forms. Some look like globes enclosed in the rocks; and in the fractures of these globes we perceive the strata of which they are composed.

Fig. 2. represents the basaltes at the foot of this promontory on the south side. The little mounts into which it appears to be collected, are sometimes only one French foot in diameter, sometimes fix. They are composed of small prisms or needles, or of cubic trapezoids, and consist of a matter distinguished by the name of dirty lava. It is made up of pozzolana, consolidated: BAS

Basaltes. solidated by a certain liquid, which, while it has communicated solidity to the pozzolana, has at the same time suffered that substance to shrink considerably, in such a manner as to leave large chinks between the pieces of basaltes, which are thus formed by the operation of the liquid on the pozzolana. It appears also to have insinuated itself into the clay with which the promontory is covered; which is become hard in its turn, and which has also split into chinks that appear to contain a kind of hard matter.

These descriptions and figures will serve to give an idea of the appearance of the basaltes, which is now generally accounted a kind of marble. Wallerius considers it as a species of the corneous or horn-rock; and Cronfiedt enumerates it among those substances which he calls garnet earths. The largest block of this stone that ever was seen, was placed according to Pliny, by Vespasian in the temple of Peace. It represented the figure of Nilus, with 16 children playing about it, denoting as many cubits of the rise of the river. The statue of Mennon, in the temple of Serapis at Thebes, which founded at the rising of the sun, was also made of the same material, if we may believe this author. Most of the Egyptian figures are likewise made of basaltes. Some of the ancients call it lapis Lydium, from Lydia, where it seems it was formerly found in great abundance. The moderns denominate it the touch-stone, as being used for the trial of gold and silver.

Various substances are found intermixed with basaltes, mixed with it; of which Mr Hamilton, in the letters above-mentioned, enumerates the following: 1. Extensive layers of red ochre, varying in all degrees from a dull ferruginous colour to a bright red, answering very well for coarse painting. 2. Veins of iron ore, sometimes very rich, commonly of a very brown or reddish cast, at other times of a blue colour. 3. Steatites, generally of a greenish foamy appearance, more rarely of a pure white, and raising an imperfect faponaceous froth when agitated with water. 4. Zeolite, of a bright and pure white colour; in masses, varying in weight from a grain to a pound; generally disposed in cavities of the cellular basaltes; often affecting a crystallization, in which the fibres proceed as rays from a centre; and in some instances have a beautiful spangled appearance, resembling that of thistle-down. The most remarkable property of this substance is, that with any of the mineral acids, but especially with that of nitre, it forms a gelatinous mixture in the course of a few hours. 5. Peperino stone, a friable matrix of indurated clay and iron, studded with little bits of zeolite or other substances; and which is often of a reddish burnt colour. 6. Pumice-stone of a black colour, containing iron not entirely dephlogisticated, but still acting on the magnetical needle.

These substances are met with among the basaltes of the Giant's Causeway in Ireland. In other places its attendants may perhaps vary according to circumstances. The basaltes itself has been considered by some as a crystallization from water; but others strenuously maintain that it is only a species of lava, and in defence of these opinions very considerable disputes have been carried on. The following is a state of the arguments on both sides from Mr Hamilton's treatise already mentioned.

In support of the volcanic origin of the basaltes it has been argued,

1. That it agrees almost entirely with lava in its elementary principles, in its grain, the species of the foreign bodies it includes, and all the diversities of its texture.

2. The iron of the basaltes is found to be in a metallic state, capable of acting on the magnetical needle, which is also the case with that found in compact lava.

3. The basaltes is fusible per se; a property which it has in common with lavas.

4. The basaltes is a foreign substance superinduced on the original limestone-soil of the country, in a state of fulnels capable of allowing the flints to penetrate considerably within its lower surface.

5. Those extensive beds of red ochre which abound among our basaltes are supposed to be an iron earth reduced to that state by the powerful action of heat; for such a change may be produced on iron in our common furnaces, provided there be a sufficient influx of fresh air; and the basaltes itself, in such circumstances, is easily reducible to an impure ochre. This is also found to take place in the living volcanoes, particularly within their craters; and is therefore supposed to afford a presumptive argument of the action of fire in the neighbourhood of basaltes.

6. Though zeolite is not yet proved to be the actual production of a volcano, yet its presence is always supposed to give countenance to this hypothesis; because zeolite is found in countries where the action of subterraneous fire is still visible, and where there is reason to believe that the whole soil has been ravaged by that principle. Thus it abounds in Iceland, where the flames of Hecla yet continue to blaze; and in the isle of Bourbon, where there is still a volcano in force. It is therefore supposed to arise from the decomposition of the products of a volcano, where the fires have been long extinct.

7. Crystals of schorl appear in great plenty among many kinds of our basaltes; and these, though not absolutely limited to volcanic countries, yet being found in great abundance among the Italian lavas, in circumstances exactly corresponding to those of our basaltes, are thought to supply a good probable argument in the present case.

8. The peperino stone is thought to be undoubtedly of a volcanic origin. It has frequently the burnt and spongy appearance of many of the volcanic products; and that of the Giant's Causeway agrees exactly with the peperino of Iceland and Bourbon.

9. Pozzolane earth is met with among the basaltes of France; and there is very little reason to doubt that our basaltes, if pulverized, would agree with it in every respect; that is, it would produce a fine sharp powder, containing the same elementary parts, and probably agreeing with it in its valuable uses as a cement. This earth is also found in the Canary islands, which are thought to have other marks of fire; it is met with in all the volcanized parts of Italy, and is never found excepting where there are other evident marks of fire.

10. Pumice-stone is universally allowed to be produced by fire, and indeed bears the resemblance of a cin- der so obviously, that one must be instantly convinced of its original. This is also found among the basaltes of Ireland.

11. There are three living volcanoes, within whose neighbourhood the basaltes and most of its usual attendant fossils have been observed, viz. Aetna in Sicily, Hecla in Iceland, and the island of Bourbon on the coast of Africa. To which it may be added, that it is found throughout all the volcanized parts of Italy, though not anywhere immediately in the neighbourhood of Vesuvius. Sir William Hamilton, however, informs us, that in the year 1799 he "picked up some fragments of large and regular crystals of close-grained lava or basalt; the diameter of which, when the prisms are complete, might have been eight or nine inches." He observes, that Vesuvius does not exhibit any lavas regularly crystallized, and forming what are called Giants Causeways, except a lava that ran into the sea, near Torre del Greco, in the year 1631, which has a small degree of such an appearance. As the fragments of basaltes which he found on this mountain, however, had been evidently thrown out of the crater in their proper form, he puts the question, "May not lavas be more ready to crystallize within the bowels of a volcano than after their emission? And may not many of the Giants Causeways already discovered be the nuclei of volcanic mountains, whose lighter and less solid parts may have been worn away by the hand of time?" Mr Faujas de St Fond gives an example of basalt columns placed deep within the crater of an extinguished volcano.

12. It is well ascertained by experience, that there are vast beds of pyrites dispersed through the interior parts of the earth at all depths; and it is also a certain fact, that this compound substance may be decomposed by the accidental effusion of water, in such a manner as to become hot, and at last to burn with great fury. This accession of pyrites is by many supposed to be the true origin of the volcanic fire; and an argument for this is, that the present volcanoes do pour forth great quantities of the component parts of pyrites, particularly sulphur, iron, and clay. Now, among the superinduced substances of the county of Antrim, and the fame may probably be said of every other basaltic country, it is certain that the quantity of iron and clay diffused through almost every species of fossil, amounts to more than one-half of the whole material; so that two of the principal elements of the pyrites are still found there, reduced in many instances to a flag or scoria. The third principle, viz. the sulphur, cannot be expected to remain; because sulphur is totally consumed by combustion; and what might perhaps escape and be sublimed would no doubt have since perished by decomposition, in consequence of being exposed to the air.

13. Another argument, which to Sir William Hamilton appears very convincing, is, that glass sometimes takes on the appearance of prisms, or crystallizes in cooling. He received some specimens of this kind from Mr Parker of Fleet-street, who informed him that a quantity of his glass had been rendered unserviceable by taking such a form. Some of these were in laminae, which may be easily separated, and others resemble basaltic columns in miniature, having regular faces. "Many of the rocks of lava in the island of Ponza (says he) are, with respect to their configurations, strikingly like the specimens of Mr Parker's glass above mentioned; none being very regularly formed basaltes, but all having a tendency towards it. Mr Parker could not account for the accident that occasioned his glass to take the basaltic form; but I have remarked, both in Naples and Sicily, that such lavas as have run into the sea are either formed into regular basaltes, or have a great tendency towards which runs such a form. The lavas of Mount Aetna, which ran into the sea near Jacin, are perfect basaltes; and a lava that ran into the sea from Vesuvius, near Torre del Greco in 1631, has an evident tendency to the basaltic form."

In opposition to these arguments it is urged, that in many of the countries where basaltes most abound, there are none of the characteristics of volcanic mountains. They assert, therefore, that the basaltes is a fossil, very extensively spread over the surface of the earth; and that, where it is found in the neighbourhood of volcanic mountains, we ought to suppose these to be accidentally raised on a basaltic soil rather than to have created it. But the advocates for the volcanic system are not much embarrassed with this argument. According to them, the basaltes has been formed under the earth itself, and within the bowels of these very mountains; where it could never have been exposed to view until, by length of time or some violent shock of nature, the incumbent mafs must have undergone a very considerable alteration, such as should go near to destroy every exterior volcanic feature. In support of this it may also be observed, that the promontories of Antrim do bear evident marks of some very violent convulsion, which has left them in their present situation; and that the island of Bagherry, and some of the Western isles of Scotland, do really appear like the surviving fragments of a country, great part of which might have been buried in the ocean. It is further added, that though the exterior volcanic character be in a great measure lost in the basaltic countries; yet this negative evidence can be of little weight, when we consider, that the few instances where the features have been preserved afford a sufficient answer to this objection. Thus the Montagne de la Coupe in France still bears the marks of its having been formerly a volcano: and this mountain is observed to stand on a base of basaltic pillars, not disposed in the tumultuary heap into which they must have been thrown by the furious action of a volcanic eruption, tearing up the natural soil of the country; but arranged in all the regularity of a Giant's Causeway, such as might be supposed to result from the crystallization of a bed of melted lava, where rest and a gradual refrigeration contributed to render the phenomenon as perfect as possible.

To these arguments stated by Mr Hamilton we shall Mr Parker's argument from another from Mr Ferber: viz. That at the time he went from Rome to Offia they were paving the road with a species of black lava. In some of the broken found in pieces he observed little empty holes, of the bigness of a walnut, incrustated all around their sides by white or amethystine, femipellucid, pointed, or truncated pyramidal crystallizations, entirely resembling the agate nodules or geodes, which are commonly filled with quartz crystallizations. There was no crack or fissure in BAS

Basaltes.

in the ambient compact lava; the crystal fibers were pretty hard, and might rather be called quartz. Some fine brownish dust lay in the rest of the holes, as impalpable and light as ashes. He tells us also, that in the greatest part of the Paduan, Veronese, and Vicentine lavas, we meet with an infinite quantity of white polygonal fiberl crystallizations, whose figure is as regular, and fill more polygonal, than the basaltes.

These may be considered as the principal arguments in favour of the volcanic theory of basaltes. On the other hand, the late celebrated Mr Bergman expresses himself to the following purpose.

"Ten years ago it was a general opinion, that the surface of the earth, together with the mountains, had been produced by moisture. It is true that some declared fire to be the first original cause, but the greater number paid little attention to this opinion. Now, on the contrary, the opinion that subterraneous fire had been the principal agent gains ground daily; and every thing is supposed to have been melted, even to the granite. It is not improbable, that both the fire and water have contributed their share in this operation; though in such a proportion, that the force of the former extends much farther than the latter; and, on the contrary, that the fire has only worked in some parts of the surface of the earth. It cannot be doubted that there has been some connection betwixt the baltic pillars and subterraneous fire; as they are found in places where the marks of fire are yet visible; and as they are even found mixed with lava, tephra, and other substances produced by fire.

"As far as we know, nature makes use of three methods to produce regular forms in the mineral kingdom. 1. That of crystallization or precipitation; 2. The crusting or settling of the external surface of a liquid mass while it is cooling; and, 3. The bursting of a moist substance while it is drying.

"The first method is the most common; but to all appearance, nature has not made use of it in the present case. Crystals are seldom or never found in any quantity running in the same direction; but either inclining from one another, or, what is still more common, placed towards one another in sloping directions. They are also generally separated a little from one another when they are regular. The nature of the thing requires this, because the several particles of which the crystals are composed must have the liberty of obeying that power which affects their constitution. The baltic columns, on the contrary, whole height is frequently from 30 to 40 feet, are placed parallel to one another in considerable numbers, and so close together that the point of a knife can hardly be introduced between them. Besides, in most places, each pillar is divided into several parts or joints, which seem to be placed on one another. And indeed it is not uncommon for crystals to be formed above one another in different layers, while the solvent has been visibly diminished at different times: but then the upper crystals never fit so exactly upon one another as to produce connected prisms of the same length or depth in all the strata taken together; but each stratum, separately taken, produces its own crystals.

"Precipitation, both in the wet and dry way, requires that the particles should be free enough to arrange themselves in a certain order; and as this is not practicable in a large melted mass, no crystallizations appear, excepting on its surface or in its cavities. Add to this, that the basaltes in a fresh fracture do not show a plain smooth surface under the microscope; but appear sometimes like grains of different magnitude, and at other times resemble fine rays running in different directions, which does not correspond with the internal structure of crystals.

"Hence the opinion of basaltes being formed by crystallization either in the wet or dry method must become less probable; but it must not be omitted, that the spars exhibit a kind of crystallization, which at first sight resembles a heap of basaltes, but upon a closer examination a very great difference is to be found. The form of the spar is everywhere alike, but the basaltes differ from one another in size and the number of their sides. The former, when broken, consists of many small unequal cubes; but the basalt does not separate in regular parts, &c. &c.

"Nature's second method of producing regular forms is that of crustling the outer surface of a melted mass. By a sudden refrigeration, nature, to effect this purpose, makes use of polyhedral and irregular forms. If we suppose a considerable bed which is made fluid by fire, and spread over a plain, it evidently appears, that the surface must first of all lose the degree of heat requisite for melting, and begin to congeal. But the cold requisite for this purpose likewise contracts the uppermost congealed stratum into a narrower space; and consequently causes it to separate from the remaining liquid mass, as the side exposed to the air is already too stiff to give way. In this manner a stratum is produced, running in a parallel direction with the whole mass; others are still produced by the same cause in proportion as the refrigeration penetrates deeper. Hence we may very plainly see how a bed may be divided into strata. In the same manner the refrigeration advances on the sides; which consequently divides the strata into polyhedral pillars, which can hardly ever be exactly square, as the strongest refrigeration in the inner parts of the mass advances almost in a diagonal line from the corners. If we add to this, that a large mass cannot be equal through its composition, nor everywhere liquid in the same degree, it will be easy to discover the cause of several irregularities. If the depth of the bed be very considerable in proportion to its breadth, prismatic pillars without cross divisions will be formed at least lengthwise from the uppermost surface downwards.

"The third way is perfectly similar to the preceding in its effect; but it is different from it by the mass being soaked in water, and by the bursting of it asunder, being the effect of the contraction while it is drying. If we suppose such a bed to be spread over a level space, the drying advances in the same manner as the refrigeration in the former case. This separation into strata properly happens when a considerable quantity of clay enters into the whole composition, because the clay decreases more than any other kind of earth in drying.

"It is most probable, therefore, that the pillars have been produced out of the baltic substance while it was yet soft, or at least not too hard to be softened by exhalations. If we therefore suppose a bed to be formed, according to spread over a place where a volcano begins to work, this theory, Basaltes. It is evident that a great quantity of the water always present on such occasions must be driven upwards in exhalations or vapours; which, it is well known, pos- sels a penetrating softening power, by means of which they produce their first effect: but when they are increased to a sufficient quantity, they force this tough moist substance upwards: which then gradually falls, and during this time bursts in the manner above de- scribed.

"The reasons for this supposition are as follows: 1. We do not find the internal substance of the basaltes melted or vitrified; which, however, soon happens by fusion; and for which only a very small degree of fire is requisite. It is of consequence very hard to explain how this substance could have been so fluid that no traces of bubbles appear in it; and yet, when broken, seem dull and uneven. Lava is seldom vitrified within; but the greater number of bubbles and pores which are found in the whole mass, are more than sufficient proofs, that it has not been perfectly melted to its smallest parts, but has only been brought to be near fluid. Secondly, the basaltes so much resemble the finer trap, both in their grain and original composition, that they can hardly be distinguished in small fragments."

Mr Kirwan is of opinion, that the basaltes owe their origin both to fire and water: they seem to have been at first a lava; but this, while immersed in water, was so diffused or dissolved in it with the affluence of heat, as to crystallize when cold, or coalesce into regular forms. That basaltes is not the effect of mere fusion he concludes with comparing its form with its texture. Its form, if produced by fusion, ought to be the effect of having flowed very thin; but in that case its texture should be glassy: whereas it is merely earthy and devoid of cavities. Hence we may understand how it comes to pass that lava perfectly vitrified, and even water, have been found enclosed in basaltes.

Mr Houel, in his Voyage Pittoresque, is at considerable pains to account for the origin of the different species of basaltes he met with in the neighbourhood of Aetna. "Some modern writers (says he) attribute the configuration of the basaltes to the sudden cooling of the lava, in consequence of the effects produced upon it by the coldness of sea-water, when it reaches the sea in a state of fusion. They suppose that the shock, which it then receives, is the cause of those different configurations which this substance assumes; the most remarkable of which have been already mentioned. This assertion, however, seems to be ill founded. By considering the basaltic rock, the first of the Cyclops represented in the plate, we find that the pile is not in its original state, and that the series of columns is at present incomplete. It is very probable, that the species of clay found there, and which is extraneous to the basaltes, has by some means taken possession of its place; and it likewise appears, that not one of the basaltes here described is entire.

"It seems, incredible, however, that a mass of matter reduced by fire to a state of liquefaction, and flowing into the sea, should be suddenly changed into regular figures by the shock of coming into contact with cold water; and that all the figures which are thus formed should be disposed in the same manner with regard to one another. For if we suppose that the water made its way into the cavity of the lava at the instant when it retreated backwards, then might the same quantity of water penetrate into the most remote parts of the mass; and by that means prolong the cavity which it had begun to form when it first entered the mass. The water then being lodged within this burning mass, and being in a state of dilatation, would have expelled whatever opposed it, and swelled the whole mass in such a manner as to form much larger interstices than those which appear between the basaltic columns; since these are everywhere in close contact with one another. Besides, how could the sudden cooling of the lava divide the upper part and sides of such an enormous mass as exactly as if they had been cast in a mould made on purpose?

"It remains also for those who adopt the hypothesis in question to explain how the shock occasioned by the cold water should make itself felt beyond a certain depth; since the very first moment it comes into contact with the liquid lava, it must cease to be cold; for the lava cannot but communicate to it a greater degree of heat than it communicates of cold in return, as the water is more easily penetrable by the burning lava than the mass of lava by the surrounding water. But farther, if at the first moment after the lava enters the water it were cooled and contracted, the water would soon prevent, by the contraction of its whole surface, any continuation of the effect which it had first occasioned.

"This seems to be the great difficulty: for how is it thus possible for the water to extend its influence to the centre of any very considerable mass? and even supposing it to act at the centre, how could it be able to fix the common centre of all the different columns?

"Let us next consider what a degree of ebullition must take place in the water when it receives such a vast quantity of water heated not only more intensely than common fire, but than red-hot iron! Though that mass, 100 fathoms in diameter, were to proceed from the bottom of the sea; or though it were immersed in it, the degree of ebullition would still be the same; and it is difficult to conceive what shock can be occasioned by a cold which does not exist, on a mass which burns, or causes to boil, whatever comes near it.

"One peculiarity attending the basaltes is, that it remains fixed in the recess which it has once occupied. Another, not less essential, is its power of dividing itself in the midst of any one of its hardest parts, and to form two distinct pieces, one of which is always con- cave, and the other convex; a division which seems the most singular curiosity of the whole.

"A third peculiarity might still be found in the interior part of these columns, if we were to meet with any that had suffered more by the lapse of time than those already described; but it is impossible for all this to be effected by water. How can water, which is everywhere the same, and which may be expected always to produce the same effects, produce such a variety on basaltes by mere contact?

"The cause of all these varieties, therefore, seems to be this, that these lavas are originally composed of materials extremely different in their natures, and from which such a variety of effects naturally proceed. The same species of matter, when actuated by the same cause, will constantly produce the same effects. This variety of effects therefore is much less owing to the influence of the water, than to the variety of materials of which those lavas are composed; and these are combined in different forms and quantities, according to the nature and quantity of the various materials which have been reduced by the volcano to a state of fusion.

"The form of the basaltes therefore proceeds from two causes. One of them, viz. the cooling, belongs indifferently to every species, independent of its meeting with water. The other is the diversity of the quantities and of the materials of which the lava is composed. From these causes alone proceed all the beauties and varieties which are beheld with admiration in this class of bodies. These take place, from the most irregular fractures in the lava, to those which display the greatest exactness and symmetry. Every new erupted lava differs from those which preceded it, and from those which will follow. In the various principles of these lavas we must seek for the causes of those cavities discoverable in the basaltes, and for the causes which produce those basaltes, at the time when the matter of which it is composed contracted itself, and consolidated all its parts. In the act of condensation, it appears to have formed various foci, around which we may distinguish the line which sets bounds to the power of each of them; and this is the line which marks the spaces intervening between the different pieces: because all of them are possessed of the same attractive force. The first emitted by the lava, at the time the basaltes is formed, produces upon it the same effect that is produced by the evaporation of the aqueous moisture from those bodies where water forms a part of the original constitution; which bodies harden in proportion as they become dry, by reason of the approach of their constituent parts to one another. The abstraction of fire produces the same effect upon basaltes, by suffering its component parts to come into closer union.

"A new proof of this theory is deducible from the form of the basaltes represented Plate LXXXVII. fig. 2. The interfaces there are pretty numerous; because the lava being of that species denominated dirty, and consisting of parts, most of which have but little solidity, they have left much larger spaces between them at their contraction. From this want of solidity we may perceive how much the basaltic mass lost of the fire by which it was dilated while in a state of fusion.

"The void spaces left by the contraction of the basaltes, are filled with a spongy matter, which by drying has also left large interfaces: and these have been filled in their turn with a kind of yellow matter similar to that which covers the promontory of Castel d'Iaci.

"Whatever variety of forms we meet with among the basaltes, and whatever divisions and subdivisions may be observable among these varieties, they are owing, 1. To the minuteness; 2. To the homogeneous nature; or, 3. To the diversity among the particles which compose the basaltes. Among the varieties already enumerated, we find reddish, earthy, soft and porous substances, together with the zeolite crystals. We see others extremely hard and compact, very finely grained, and containing likewise felschel and zeolite crystals. Others are very hard and dense, which appear to be a mixture of fine gray and white bodies; and of each of these colours many different shades, from light to darker, containing also zeolite crystals. Lastly, we find some consisting of a matter similar to clay, mixed with round black lands.

"It may be objected, that the late eruptions of Aetna afford no basaltes, nor have they any divisions similar to those above mentioned. But to this we may reply, that if they afford neither such basaltes, nor such regular divisions, the reason is, that neither their quantity, nor the ingredients of which they are composed, are such as are necessary for the production of basaltes: and for a proof of this we may refer to lavas of the most remote antiquity, which have no more resemblance to basaltes than those that are more modern.

"Lastly, an argument, to which no plausible reply can be made, that the basaltes are not formed by sea-water, is, that in the year 1669, the lava of Mount Aetna ran into the sea for two leagues and a half, without having the least appearance of being converted into basaltes."