COALLERY, or COLLIERY; a coal-History of work, or place where Coals are dug.

It is generally agreed, that our cannel-coal * is the lapis amplexites of the Romans; though it seems to have been used by them only for making toys, bracelets, &c. But of that common fuel which we denominate coals, the native Romans were entirely ignorant. It is certain that they are not, as some have imagined, the lapis obsidianus of Pliny, about which there have been been great disputes: nor the Gagates, or Jet, which others, again, have taken for the lapis olifidianus; though the lightness and texture show plainly that it is not either stone or coal. In fact, there are no beds of it in the compass of Italy. The great line of that fuel seems to sweep away round the globe, from north-east to south-west; not ranging at a distance even from the south-easterly parts of our island, as is generally imagined, but actually visiting Brabant and France, and yet avoiding Italy.

But the primeval Britons appear to have used it. And in the precincts of Manchester particularly, which are furnished with an inexhaustible abundance of it, they could not have remained unapprised of the agreeable combustible around them. The currents there frequently bring down fragments of coal from the mountains; and in the long and winding course of them through the parish, the Britons would soon mark the shining stones in the channels; and by the aid of accident, or the force of reflection, find out the utility of them. But we can advance still nearer to a certainty. Several pieces of coal were discovered some years ago in the land under the Roman way to Ribchester, when both were dug up at the construction of a house in Quay-street. The number of pieces, several of them as large as eggs, was not less than 40; and a quantity of slack was dug up with them. These circumstances show the coals to have been lodged upon the spot, before the road of the Romans covered it. That ground being in the neighbourhood of Manchester, the Britons had there reposited a quantity of coals, probably for the use of the garrison; and many of the smaller fragments, and some of the slack, were buried in the land upon which they were laid. And that the Britons in general were acquainted with this fuel, is evident from its appellation amongst us at present, which is not Saxon, but British; and subsists among the Irish in their O'guel, and among the Cornish in their kolan, to this day.

The extensive beds of fuel, therefore, with which the kingdom of England and the precincts of Manchester are so happily stored, were first noticed by the skill, and first opened by the labour of the Britons; and some time before the arrival of the Romans amongst us. And the nearer quarries in the confines of Bradford, Newton, and Manchester, would naturally attract the notice, and invite the inquiries, of the Britons, before any others. The current of the Medlock, which washes the sides of them, would bring down specimens of the riches within, lodge many of them about the Castlefield, and allure the Britons successively to a collection of the one and a search after the other.

But, even for ages after the discovery, wood continued to compose the general firing of the nation. In 852, a grant was made of some lands by the abbey of Peterborough, under the reservation of certain boons and payments in kind to the monastery; as, one night's entertainment; 10 vessels of Welsh and two of common ale; 60 cart-loads of wood; and 12 of pit-coal; where we see the quantity of coal was only one cart-load to five of wood. The latter naturally continued the principle article of our fuel as long as the forests and thickets presented themselves to ready to the hand; and fuel it continued till a very late period. The first public notice of the former is mentioned by Mr Hume to have been in the time of Henry III. who, in the year 1272, granted a charter to the town of Newcastle, giving the inhabitants a licence to dig coals; and the first statute relating to this article was the 9 Henry V. c. 10, ordaining all keels in the port of Newcastle to be measured by commissioners, before carriage of coals, on pain of forfeiture. They were not brought into common use till the reign of Charles I.; and were then sold for about 17s. a chaldron. In some years after the restoration, there were about 200,000 chaldrons burnt in London; in 1670, about 270,000 chaldrons; and at the revolution, upwards of 300,000 chaldrons; and at present, full 600,000 are annually consumed there. There is, besides, an immense consumption in other parts of Britain, and in Ireland. In Scotland, they supply their own consumption, and also export. In Ireland, though they have coal, yet they take annually to the value of 30,000l. from England, and 12,000l. from Scotland.

The most remarkable colliery, or coal-work, that we have ever had in this island, was that wrought at Burrowhounells, under the sea. The veins of coal were found to continue under the bed of the sea in this place, and the colliers had the courage to work the vein near half way over; there being a mote half a mile from the shore, where there was an entry that went down into the coal-pit, under the sea. This was made into a kind of round key or mote, as they call it, built so as to keep out the sea, which flowed there twelve feet. Here the coals were laid, and a ship, of that draught of water, could lay her side to the mote, and take in the coal.—This famous colliery belonged to the earl of Kincardine's family. The fresh water which sprung from the bottom and sides of the coal pit, was always drawn out upon the shore by an engine moved by water, that drew it forty fathom. This coal-pit continued to be wrought many years to the great profit of the owners, and the wonder of all that saw it; but, at last, an unexpected high tide drowned the whole at once; the labourers had not time to escape, but perished in it.

There are several other countries in Europe which possess considerable coal-mines; as France, Liege, Germany, and Sweden. Also on the other side of the Atlantic ocean, there has been coal discovered, and wrought; in Newfoundland, Cape-Breton, Canada, and some of the New-England provinces. But in all these countries, the coal is of a quality much inferior to the of the British, and entirely unfit to be used in many manufactory factories; so that they are obliged to import great quantities from Britain for the use of their manufactures of iron, &c.

Our inland coal trade, that is, carrying coals from Newcastle, Sunderland, Blith, and other adjacent places in the north of England, as also from the frith trade of Edinburgh in Scotland, and other places therabouts, to the city of London, and to the port-towns on the coast all the way, as well on this side of Newcastle, north, as up the channel as high as Portsmouth west, is a prodigious article, and employs abundance of shipping and seamen; in so much that, in a time of urgent necessity, the coaly navigation alone has been able to supply the government with a body of seamen for the royal navy, able to man a considerable fleet at a very short warning, and that without difficulty, when no other branch of trade would do the like. Likewise the Whitehaven coaleries in Cumberland, belonging to Sir James Lowther, furnish several counties in Ireland with coals, and constantly employ upwards of 2000 seamen; which also is a noble nursery for the navy of this kingdom. And not only do the pit-coals sufficiently supply all the ports, but, by means of those ports and the navigable rivers, all the adjacent counties very far inland.

In short, coals, though not an exclusive, yet may, with propriety, be styled a peculiar blessing to Britain from their great plenty, their acknowledged excellence, and their being found in such places as are conveniently situated for exportation. Nor is there any danger of the export-trade being lessened even by the several duties that have been laid upon them; for the foreign consumption being founded in necessity with regard to manufactures, and in economy where they are used for convenience (wood and turf being dearer than coals with the duty), we need be in no fear of the markets declining. There is as little room to be alarmed from an apprehension of their being exhausted, as the present works are capable of supplying us for a long series of years, and there are many other mines ready to be opened when these shall fail. Besides, there are known to be coals in many parts of the three kingdoms, which hitherto they have had no encouragement to work.

Besides the value of this commodity as a convenience of life, as an article of commerce, and as giving rise to a nursery of seamen for the increase of the marine; other important advantages deserve to be noticed. Coals are in many respects, and in a very high degree, useful to the landed interest; not only by raising exceedingly the real value, and of course the purchase, of those lands in which they are found, and those through which it is necessary to pass* from the works to the places where they are embarked, but from the general improvements they have occasioned; so that very few counties are now better cultivated than Northumberland, and the same effects they have had in a greater or lesser degree in other places. Thousands of laborious people are employed in and about the mines; thousands more in conveying them to the ports, and on board the ships; to say nothing of those that draw their subsistence from the carriage of them by land to supply families, &c. There are also great numbers that live in a superior station; as stewards, directors, factors, agents, book-keepers, &c. To these we may add the extraordinary encouragement given to ingenious artists who have invented, and the numerous workmen continually employed about those several curious and costly machines which, for a variety of purposes in this business, are in continual use, and of course in continual wear: we may join to these the multitudes that obtain their living from the many manufactures in which they are employed, and which could not be carried on but by the help and cheapness of coals. Lastly, the produce of coals exported, which amounts to a very considerable sum, besides being profitable to the owners, merchants, and mariners, is so much clear gain to the nation.

It might be expected, that a trade so beneficial to individuals, and to the nation in general, and which has been gradually increasing for several centuries past, would have been advanced by this time to very great perfection, and reduced to a regular system. But, in one very essential respect, it is found to be quite otherwise. The art of working coal-mines in the most profitable manner is indeed highly improved; but the fundamental of the art, that of searching for and discovering coal in any district of country where it has not yet been found, has never, that we know of, been treated in a systematic manner. The reader, therefore, will not be displeased to find this defect supplied in the course of the present article; together with a detail of all the other operations in the business of coaleries.

The terrestrial matters which compose the solid situation of parts of the earth are disposed in strata, beds, or lay-the strata, the under surface of one bearing against or lying upon the upper surface of that below it, which last bears or lies on the next below in the same manner.

These strata consist of very different kinds of matter, such as free stone, lime-stone, metal-stone or whinstone, coal, &c. as will be particularly specified in the sequel.

Some of these strata are of a considerable thickness, being often found from 100 to 200 feet or upwards, nearly of the same kind of matter from the superior to the inferior surface; and others are found of the least thickness imaginable, one inch or less.

All these strata are divided or parted from each other laterally, either by their even, smooth, polished surfaces, with very thin lamina of soft or ductile matter betwixt them, called the parting, which renders them easy to separate; or else only by the surfaces closely conjoined to each other, without any visible matter interposed betwixt them; yet the different fulness of each stratum is not in the least intermixed, though sometimes they adhere so strongly together, that it is very difficult to part or disjoin them: in this last case they are said to have a bad parting.

Besides this principal division or parting laterally, there are, in some strata, secondary divisions or partings also laterally, separating or approaching towards a separation, of the same stratum, into parts of different thicknesses, nearly parallel to each other, in the same manner as the principal partings divide the different strata from each other; but these secondary ones are not so strong or visible, nor make so effectual a parting, as the principal ones do; and are only met with in such strata, as are not of an uniform hardness, texture, or colour, from the upper to the under surface.

There are other divisions or partings, called backs, in almost every stratum, which cross the former lateral ones longitudinally, and cut the whole stratum through its two surfaces into long rhomboidal figures. These again are crossed by others called cutters, running either in an oblique or perpendicular direction to the last mentioned backs, and also cut the stratum through its two surfaces. Both these backs and cutters generally extend from the upper or superior stratum down through several of the lower ones; so that these backs and cutters, together with the lateral partings before mentioned, divide every stratum into innumerable cubic, prismatic, and rhomboidal figures, according to the thickness of the stratum, and the position and number of the backs and cutters. They

M 2 sometimes sometimes have a kind of thin partition of dusty or soft matter in them, and sometimes none, like the first mentioned partings; but the softer kind of strata generally have more backs and cutters than the harder kind, and they do not extend or penetrate through the others.

To explain this a little further, let A, B, C, D, E, F, G, (fig. 1.) represent the principal partings before mentioned, or the upper and under surfaces of any stratum; then a, b, c, d, e, f, will represent the secondary lateral partings nearly parallel to the principal ones: g, h, i, k, l, m, the longitudinal partings called backs; n, o, p, q, r, s, the cross partings called cutters, crossing the last mentioned ones either obliquely or perpendicular.

In all places where the strata lie regular, they are divided and subdivided in the manner above mentioned; and sometimes in this manner extend through a pretty large district of country; though it is often otherwise; for their regularity is frequently interrupted, and the strata broken and disordered, by sundry chasms, breaches, or fissures, which are differently denominated according to their various dimensions, and the matters with which they are filled, viz., dikes, hitches, and troubles, which shall be explained in order.

Dikes are the largest kind of fissures. They seem to be nothing but a crack or breach of the solid strata, occasioned by one part of them being broken away and fallen from the other. They generally run in a straight line for a considerable length, and penetrate from the surface to the greatest depth ever yet tried, in a direction sometimes perpendicular to the horizon, and sometimes obliquely: the same kind of strata are found lying upon each other in the same order, but the whole of them greatly elevated or depressed, on the one side of the dike as on the other. These fissures are sometimes two or three feet wide, and sometimes many fathoms. If the fissure or dike be of any considerable width, it is generally filled with heterogeneous matter, different from that of the solid strata on each side of it. It is sometimes found filled with clay, gravel, or sand; sometimes with a confused mass of different kinds of stone lying edgewise; and at other times with a solid body of freestone, or even whinstone. When the fissure is of no great width, as suppose two or three feet only, it is then usually found filled with a confused mixture of the different matters which compose the adjoining strata, consolidated into one mass. If the dike runs or stretches north and south, and the same kind of strata are found on the east side of the dike, in a situation with respect to the horizon 10 or 20 fathoms lower than on the other side, it is then said to be a dip-dike or downcast-dike of 10 or 20 fathoms to the eastward;—or counting from the east side, it is then said to be a rise-dike or upcast of so many fathoms westward. If the strata on one side are not much higher or lower with respect to the horizontal line, than those on the other, but only broken off and removed to a certain distance, it is then said to be a dike of so many fathoms thick; and from the matter contained between the two sides of the fissure or dike, it is denominated a clay-dike, stone-dike, &c.

A hitch is only a dike or fissure of a smaller degree, by which the strata on one side are not elevated or separated from those on the other side above one fathom. These hitches are denominated in the same manner as dikes, according to the number of feet they elevate or depress the strata.

There are dikes (though they are not often met with in the coal-countries) whose cavities are filled with sparry, the ores of iron, lead, vitriol, or other metallic or mineral matters; and it is pretty well known, that all metallic veins are nothing else than what in the coal countries are called dikes.

The strata are generally found lying upon each other in the same order on one side of the dike as on the other, as mentioned above, and nearly of the same thicknesses, appearing to have been originally a continuation of the same regular strata, and the dike only a breach by some later accident, perpendicularly or obliquely down through them, by which one part is removed to a small distance, and depressed to a lower situation than the other. But this is not the only alteration made in the strata by dikes; for generally to a considerable distance on each side of the dike, all the strata are in a kind of shattered condition, very tender, easily pervious to water, and debauched greatly in their quality, and their inclination to the horizon often altered.

Troubles may be denominated dikes of the smallest degree; for they are not a real breach, but only an approach towards it which has not taken a full effect. The strata are generally altered by a trouble from their regular site to a different position. When the regular course of the strata is nearly level, a trouble will cause a sudden and considerable ascent or descent: where they have, in their regular situation, a certain degree of ascent or descent, a trouble either increaseth it or alters it to a contrary position: and a trouble has these effects upon the strata in common with dikes, that it greatly debaucheth them from their original quality; the partings are separated; the backs and cutters disjoined, and their regularity disordered; the original cubic and prismatic figures, of which the strata were composed, are broken, and the dislocation filled with heterogeneous matter; and the whole strata are reduced to a softer and more friable state.

The strata are seldom or never found to lie in a true horizontal situation; but generally have an inclination or descent, called the dip, to some particular dip and part of the horizon. If this inclination be to the eastward, it is called an east dip, and a west rise; and according to the point of the compass to which the dip inclines, it is denominated, and the ascent or rise is to the contrary point. This inclination or dip of the strata is found to hold everywhere. In some places, it varies very little from the level; in others, very considerably; and in some so much, as to be nearly in a perpendicular direction: but whatever degree of inclination the strata have to the horizon, if not interrupted by dikes, hitches, or troubles, they are always found to lie in the first regular manner mentioned. They generally continue upon one uniform dip until they are broken or disordered by a dike, hitch, or trouble, by which the dip is often altered, sometimes to a different part of the horizon, and often to an opposite point; so that on one side of a dike, hitch, or trouble, if the strata have an east dip, on the other side they may have an east rise, which is a west dip; and in general, any considerable alteration in the dip is never met. To illustrate what has been said, see fig. 2, where \(a b c d\), &c., represents a course of strata lying upon each other, having a certain inclination to the horizon. A B is a downcast-dike, which depresseth the strata obliquely to \(e f g h\), &c., lying upon each other in the same order, but altered in their inclination to the horizon. C D represents a clay or free-stone dike, where the strata are neither elevated nor depressed, but only broken off and removed to a certain distance. E F, represents a hitch, which breaks off and depresseth the strata only a little, but alters their inclination to the horizon. G H, represents a trouble, where the strata on one side are not entirely broken off from those on the other, but only in a crushed and irregular situation.

As some particular strata are found at some times to increase, and at other times to diminish, in their thicknesses, whilst others remain the same, consequently they cannot be all parallel; yet this increase and diminution in their thicknesses comes on very gradually.

The strata are not found disposed in the earth according to their specific gravities: for we often find strata of very dense matter near the surface; and perhaps at 50 or even 100 fathoms beneath, we meet with strata of not half the specific gravity of the first. A stratum of iron ore is very often found above one of coal, though the former has twice the gravity of the latter; and, in short, there is such an absolute uncertainty in forming any judgment of the disposition of the strata from their specific gravities, that it cannot in the least be relied upon.

It has been imagined by many, that hills and valleys are occasioned by those breaches in the strata before mentioned called dikes; but this is contradicted by experience. If it was so, we should meet with dikes at the skirts of the hills, and by the sides of valleys, and the sea-shore; but instead of that, we generally find the strata lying as uniformly regular under hills and valleys, and beneath the bottoms of the sea (as far as has been yet tried), as in the most champaign countries. It may happen, indeed, that a dike is met with in some of these places; but that being only a casual circumstance, can never be admitted as a general cause. Whatever irregularities are occasioned in the solid strata by dikes, or other breaches, are commonly covered over and evened by those beds of gravel, clay, sand, or soil, which lie uppermost, and form the outward surface of the earth. Wherever these softer matters have been carried off, or removed by accident, as on the tops of hills and the sides of valleys, there the solid strata are exposed, and the dip and rise and other circumstances of them may be examined; but no certain conclusions can be drawn, merely from the unevenness and inequalities of the outward surface.

The preceding observations, upon the general disposition of the solid strata, are equally applicable to the strata of coal as to those of stone or other matter.

We shall next give an account of the several strata of coal, and of stone and other matters, which are usually connected with coal, and are found to have a particular affinity with it: and, for the sake of distinction, shall arrange them into six principal classes, which will include all the varieties of strata that have been found to occur in all those districts of country both in Scotland and England where coal abounds.

1. Of Whinstone.] The strata of what is denominated whinstone are the hardest of all others; the angular pieces of it will cut glass; it is of a very coarse texture, and when broke across the grain exhibits the appearance of large grains of sand half vitrified; it can scarcely be wrought, or broke in pieces, by common tools without the assistance of gun-powder; each stratum is commonly homogeneous in substance and colour, and cracked in the rock to a great depth. The most common colours of these strata are black or dark blue, yet there are others of it ash-coloured and light brown. Their thickness in all the coal countries is but inconsiderable, from five or six feet down to a few inches; and it is only in a few places they are met with of these thicknesses. In the air it decays a little, leaving a brown powder; and in the fire it cracks, and turns reddish brown. Limestone, and what is called flaggared limestone, is sometimes, though rarely, met with in coaleries. It is a well known stone; but from its resemblance in hardness and colour is often mistaken for a kind of whinstone. Sometimes, particularly in hilly countries, the solid matter next the surface is found to be a kind of soft or rotten whinstone;—but it may be noted, that this is only a mass of heterogeneous matter disposed upon the regular strata; and that beneath this, all the strata are generally found in as regular an order as where this heterogeneous matter does not occur.

2. Of Poit-stone.] This is a free stone of the hardest kind, and next to the limestone with respect to hardness and solidity. It is of a very fine texture; and when broken appears as if composed of the finest sand. It is commonly found in a homogeneous mass, though variegated in colour; and, from its hardness, is not liable to injury from being exposed to the weather. Of this kind of stone there are four varieties, which may be distinguished by their colour: the most common is white poit, which in appearance is like Portland stone, but considerably harder; it is sometimes variegated with streaks or spots of brown, red, or black.

Grey poit is also very common; it appears like a mixture of fine black and white sand; it is often variegated with brown and black streaks; the last mentioned appear like small clouds composed of particles of coal.

Brown or yellow poit is often met with of different degrees of colour; most commonly of the colour of light ochre or yellow sand; it is as hard as the rest, and sometimes variegated with white and black streaks.

Red poit is generally of a dull red colour: this is but rarely met with; it is often streaked with white or black.

All these lie in strata of different thicknesses; but commonly thicker than any other strata whatever: they are separated from each other, and from other kinds of strata, by partings of coal, sand, or soft matter of different colours which are very distinguishable.

3. Of Sandstone.] This is a free stone of a coarser texture than poit, and not so hard; is so lax as to be easily pervious to water; when broke, is apparently of a coarse sandy substance; is friable and moulders to sand when exposed to the wind and rain; has frequently white shining spangles in it, and pebbles or other small stones inclosed in its mass. Of this, there are two kinds commonly met with, distinguished by their colours, grey and brown, which are of different shades, lighter or darker in proportion to the mixture of white in them. It is most generally found in strata of considerable thicknesses, without many secondary partings; and sometimes, though rarely, it is subdivided into layers as thin as the common grey slate. It has generally sandy or soft partings.

4. Of Metal-stone.] This is a tolerable hard stratum, being in point of hardness next to sand-stone; generally solid, compact, of considerable weight, and of an argillaceous substance, containing many nodules or balls of iron ore, and yellow or white pyrites; its partings, or the surfaces of its strata, are hard, polished, and smooth as glass. When broke, it has a dull dusty appearance (though of a fine texture), like hard dried clay mixed with particles of coal. Though hard in the mine or quarry, when exposed to the fresh air it falls into very small pieces. The most usual colour of this stone is black; but, there are several other lighter colours, down to a light brown or grey. It is easily distinguished from free-stone by its texture and colour, as well as by its other characteristics. It lies in strata of various thicknesses, though seldom so thick as the two last mentioned kinds of stone.

5. Of Shiver.] This stratum is more frequently met with in coaleries than any other. There are many varieties of it, both in hardness and colour; but they all agree in one general characteristic. The black colour is most common; it is called by the miners black shiver, black mottle, or bleas. It is softer than metal-stone, and in the mine is rather a tough than a hard substance, is not of a solid or compact matter, being easily separable, by the multitude of its partings, &c., into very small parts, and readily absorbing water. The substance of this stratum is an indurated bole, commonly divided into thin laminae unequal thicknesses, which break into long small pieces when struck with force; and, on examination, they appear to be small irregular rhomboids; each of these small pieces has a polished glassy surface; and, when broken off the grain, appears of a dry, leafy, or laminated texture, like exceeding fine clay: it is very friable; feels to the touch like an unctuous substance; and dissolves in air or water to a fine pungent black clay. There are almost constantly found inclosed in its strata lumps or nodules of iron ore; often real beds of the same.

There are other colours of this stratum besides black. The brown or dun shiver is very frequently met with; it agrees with the above description in every thing but colour. Grey shiver is also very common: it seems to be only a mixture of the black and dun; and by the different degrees of mixture of these colours others are produced. It lies in strata sometimes of considerable thickness, at other times not exceeding a few feet: they are commonly parted from each other by laminae of spar, coal, or soft matter.

6. Of Coal.] Referring the reader, for the scientific division of coals, to Ampelites, Lithanthrax, and the preceding articles, we shall here consider them as distinguishable into three kinds, according to their degrees of inflammability.

1. The least inflammable kinds are those known by the name of Welsh coal, which is found in Wales; Kilkenny coal, which is found near Kilkenny in Ireland; and blind or deaf coal, which is found in many parts of Scotland and England. This coal takes a considerable degree of heat to kindle it, but when once thoroughly ignited will burn a long time; it remains in the fire in separate pieces without sticking together or caking; it produceth neither flame nor smoke, and makes no cinder, but burns to a white stony flagg; it makes a hot glowing fire like charcoal or cinders; and emits effluvia of a suffocating nature which renders it unfit for burning in dwelling-houses, its chief use being among maltsters, dyers, &c. for drying their commodities.

2. Open burning coal, soon kindles, making a hot pleasant fire, but is soon consumed; it produceth both smoke and flame in abundance; but lies open in the fire, and does not cake together so as to form cinders, its surface being burnt to ashes before it is thoroughly calcined in the midst; from this it has its name of an open burning coal; it burns to white or brown ashes very light. Of this kind is cannel-coal, jett, parrot, splint, and most of the coals in Scotland.

3. Clofe burning coal, kindles very quickly, makes a very hot fire, melts and runs together like bitumen, the very smallest culm making the finest cinders, which being thoroughly burnt are porous and light as a pumice stone, and when broke are of a thinning lead colour; it makes a more durable fire than any other coal, and finally burns to brown or reddish coloured heavy ashes. Of this kind are the Newcastle and several other of the English coals, and the smoky coals of Scotland. The open burning and the clofe burning coal mixed together, make a more profitable fire for domestic uses than either of them separate.

In all those districts of country where coal is found, there are generally several strata of it; perhaps all the different kinds above mentioned will be found in some, and only one of the kinds in others; yet this one kind may be divided into many different teams or strata, by beds of shiver or other kinds of matter interposing, so as to give it the appearance of so many separate strata.

All these strata above described, with their several varieties, do not lie or bear upon each other in the order in which they are described, nor in any certain order, or invariable order. Though there be found the same kinds of strata in one coalery or district as in another, yet they may be of very different thicknesses. In some places there are most of the hard kinds, in others most of the softer; and in any one district it rarely happens that all the various kinds are found; for some kinds, perhaps, occur only once or twice, whilst others occur 10 or 20 times before we reach the principal stratum of coal.

In order to explain this, suppose the strata in the pit at A (fig. 3.) lie in the order a, b, c, d, &c.; they may be so much altered in their thicknesses, by reason of some of them increasing and others diminishing, at the distance of B, that they may be found there of very different thicknesses; or if they are examined in a pit at D, by reason of its lower situation, and the If the solid strata are not exposed to view, neither in the hills nor valleys of the ground under examination, then search in the adjoining grounds; and if the same kind of strata are found there as in the adjacent coaly, and there is reason, from the dip and other circumstances, to believe that they stretch through the ground to be examined; it may then be concluded that the coal is there, as well as these other strata.

Suppose a coaly is on the side of a hill at A, fig. 3, and you would search for a coal at B, on the other side of the hill, but in a much lower situation; by observing the several strata lying above the coal at A, and the point to which they dip, which is directly towards B (if clear of dikes), you may expect to find the same kind of strata on the other side of the hill, but much lower down. Accordingly, if some of the strata are visible in the face of the precipice C, they may be compared with some of those in the pit at A. Or, if they are not to be seen there, by searching in the opposite hill, they may perhaps be discovered at the place F; where, if they be found in the manner before mentioned, and there be reason to believe they extend regularly from the first place to this, it is more than probable the coal, as well as these strata, will be found in the intermediate ground.

If the ground to be examined lie more to the rise of the coal, as at E, which being supposed to be on a flat, perhaps the solid strata there may be wholly covered by the gravel, clay, &c. of the outward surface lying upon them: In this case, by measuring the horizontal distance and the descent of ground from A to E, and computing the quantity of ascent or rise of the coal in that distance; by comparing these together, it may be judged at what depth the coal will be found there, allowing that it lies regular. Thus, suppose the coal at A 80 yards deep, the distance from A to E 500 yards, and that the coal rises 1 yard in 10 yards of horizontal distance:

Then, from the depth of the pit 80 Deduct the descent of ground from A to E, suppose 24

This remainder would be the depth, if the coal was level 56 But as the coal rises 1 in 10 feet, then deduct what it rises in 500 yards, which is 50

And the remainder is the depth of that coal at E 6 Yards.

Or suppose that the place at B is 500 yards the contrary way, or to the full dip of the coal at A; if a view of the solid strata cannot be obtained, then by proceeding in the same manner as before, the depth of the coal at that place may be computed. Thus,

To the depth of the coal at the pit A 80 Add the descent or inclination of the coal in 500 yards, which, as before, is 50

This sum would be the depth, if the ground was level 130 But as the ground descends towards B, deduct the quantity of that, which suppose 80

Remains the depth of the coal at B 50 Yards. If the place to be examined be neither to the full dip nor full rise, but in some proportion towards either, the same method may be pursued, computing how much the coal rises or dips in a certain distance in that direction.

If there is known to be a dike in the workings of the pit at A, which elevates or depresseth the strata towards the place under examination, then the quantity of the elevation or depression must be accordingly added to or deducted from the computed depth of the coal at that place. Suppose there is an upcast dike of 10 fathoms or 20 yards towards B, then deduct 20 from 50, the depth before computed, there will remain 30 yards or 15 fathoms for the depth of the coal at B.

But it often happens that coal is to be searched for, in a part of the country, at such a considerable distance from all other coalyards, that by reason of the intervention of hills, valleys, unknown dikes, &c., the connection or relation of the strata with those of any other coalyard cannot be traced by the methods last mentioned; in which case a more extensive view must be taken of all circumstances than was necessary in the former; and a few general rules founded on the foregoing observations, and on conclusions drawn from them, will greatly assist in determining sometimes with a great degree of probability, and sometimes with absolute certainty, whether coal be in any particular district of country or not.

The first proper step to be taken in such a case, is to take a general view of that district of country intended to be searched, in order to judge, from the outward appearance or face of the country, which particular part out of the whole is the most likely to contain those kind of strata favourable to the production of coal; and consequently such particular part being found, is the most advisable to be begun with in the examination.

Though the appearance of the outward surface gives no certain or infallible rule to judge of the kinds of strata lying beneath, yet it gives a probable one; for it is generally found, that a chain of mountains or hills rising to a great height, and very steep on the sides, are commonly composed of strata much harder and of different kinds from those before described wherein coal is found to lie, and therefore unfavourable to the production of coal; and these mountainous situations are also more subject to dikes and troubles than the lower grounds; so that if the solid strata composing them gave even favourable symptoms of coal, yet the last circumstance would render the quality bad, and the quantity precarious. And, on the whole, it may be observed, that mountainous situations are found more favourable to the production of metals than of coal. It is likewise generally found that those districts abounding with valleys, moderately rising hills, and interspersed with plains, sometimes of considerable extent, do more commonly contain coal, and those kinds of strata favourable to its production, than either the mountainous or champain countries; and a country so situated as this last described, especially if at some considerable distance from the mountains, ought to be the first part appointed for particular examination. Plains, or level grounds of great extent, generally situated by the sides of rivers, or betwixt

Rule 6th.

Mountains and valleys.

Plains.

N° 83. monly connected with some of them, it therefore descends into the coal, where it finds a ready passage through the open backs and cutters. Sometimes, indeed, it finds some other stratum than coal to collect and transmit it to the surface; but the difference is easily distinguishable; for the ochre matter in the water, when it comes from a stratum of coal, is of a darker ruddy colour than when it proceeds from any other, and often brings with it particles and small pieces of coal; therefore, wherever these two circumstances concur in a number of these kind of springs, situated in a direction from each other answerable to the stretch or to the inclination of the strata, it may be certain the water comes off coal, and that the coal lies in a somewhat higher situation than the apertures of the springs.

There are other springs also which come off coal, and are not distinguishable from common water, otherwise than by their astringency, and their having a blue scum of an oily or glutinous nature swimming upon the surface of the water. These, in common with the others, bring out particles of coal, more especially in rainy seasons when the springs flow with rapidity. When a number of these kinds are situated from each other in the direction of the strata, as above described; or if the water does not run forth as in springs, but only forms a swamp, or an extension of stagnant water beneath the turf; in either case, it may be depended upon that this water proceeds from a stratum of coal.

If the stratum of coal is not exposed to view, or cannot be discovered by the first method of searching for the crop, although the appearance of the other strata be very favourable, and afford a strong probability of coal being there; and if the last-mentioned method of judging of the particular place where the crop of the coal may lie, by the springs of water issuing from it, should, from the deficiency of those springs or other circumstances, be thought equivocal, and not give a satisfactory indication of the coal; then a further search may be made in all places where the outward surface, or the stratum of clay or earth, is turned up by ploughing, ditching, or digging, particularly in the lower grounds, in hollows, and by the sides of streams. These places should be strictly examined, to see if any pieces of coal be intermixed with the substance of the superior lax strata; if any such be found, and if they be pretty numerous and in detached pieces, of a firm substance, the angles perfect or not much worn, and the texture of the coal distinguishable; it may be concluded, that the stratum of coal to which they originally did belong is at no great distance, but in a situation higher with respect to the horizon; and if there be also found along with the pieces of coal other mineral matter, such as pieces of flint or freestone, this is a concurrent proof, that it has come only from a small distance. Though the two foregoing methods should only have produced a strong probability, yet if this last mentioned place, where the pieces of coal, &c. are found in the clay, be in a situation lower than the springs; when this circumstance is joined to the other two, it amounts to little less than a moral certainty of the stratum of coal being a very little above the level of the springs. But if, on the contrary, these pieces of coal are found more sparingly interspersed in the superior stratum, and if the angles are much fretted or worn off, and very little of other kinds of mineral matter connected with them; it may then be concluded, that they have come from a stratum of coal situated at a greater distance than in the former case; and by a strict search and an accurate comparison of other circumstances, that particular place may be discovered with as much certainty as the other.

After the place is thus discovered, where the stratum of coal is expected to lie concealed, the next proper step to be taken, is to begin digging a pit or hole there perpendicularly down to find the coal. If the coal has no solid strata above and beneath it, but be found only embodied in the clay or other lax matter, it will not be there of its full thickness, nor so hard and pure as in its perfect state when enclosed between two solid strata, the uppermost called the roof, and the undermost called the pavement, of the coal; in such situation therefore it becomes necessary, either to dig a new pit, or to work a mine forward until the stratum of coal be found included between a solid roof and pavement, after which it need not be expected to increase much in its thickness: yet as it goes deeper or farther to the dip, it most likely will improve in its quality; for that part of the stratum of coal which lies near the surface, or only at a small depth, is often debased by a mixture of earth and sundry other impurities, washed down from the surface, through the backs and cutters, by the rains; whilst the other part of the stratum which lies at a greater depth is preserved pure, by the other solid strata above it intercepting all the mud washed from the surface.

The above methods of investigation admit of many different cases, according to the greater or less number of favourable circumstances attending each of the modes of inquiry; and the result accordingly admits every degree of probability, from the most distant, even up to absolute certainty. In some situations, the coal will be discovered by one method alone; in others, by a comparison of certain circumstances attending each method; whilst in some others, all the circumstances that can be collected only lead to a certain degree of probability.

In the last case, where the evidence is only probable, it will be more advisable to proceed in the search by boring a hole through the solid strata (in the manner hereafter described), than by digging or sinking a pit, it being both cheaper and more expeditious; and in every case, which does not amount to an absolute certainty, this operation is necessary, to ascertain the real existence of the coal in that place.

We shall now suppose, that having examined a certain district, situated within a few miles of the sea or some navigable river, that all the circumstances which offer only amount to a probability of the coal being there, and that boring is necessary to ascertain it; we shall therefore describe the operation of boring to the coal; then the method of clearing it from water, commonly called winning it; and all the subsequent operations of working the coal and raising it to the surface, leading it to the river or harbour, and finally putting it on board the ships.

Suppose that the ground, A, B, C, D, fig. 4., has been examined, and from the appearance of the strata for the coal, where where they are visible (as at the precipice D, and several other places), they are found to be of those kinds usually connected with coal, and that the point to which they rise is directly well towards A, but the ground being flat and covered to a considerable depth with earth, &c., the strata cannot be viewed in the low grounds; therefore, in this and all similar situations, the first hole that is bored for a trial for coal should be on the west side of the ground, or to the full rise of the strata as at A, where, boring down through the strata 1, 2, 3, suppose 10 fathoms, and not finding coal, it will be better to bore a new hole than to proceed to a great depth in that; therefore, proceeding so far to the eastward as B, where the stratum 1, of the first hole, is computed to be 10 or 12 fathoms deep, a second hole may be bored, where boring down through the strata 4, 5, 6, 7, 8, the stratum 1 is met with, but no coal; it would be of no use to bore farther in this hole, as the same strata would be found which were in the hole A; therefore, proceeding again so far to the eastward, as it may be computed the stratum 4 of the second hole will be met with at the depth of 10 or 12 fathoms, a new hole may be bored at C; where, boring through the strata 9, 10, 11, 12, the coal is met with at 13, before the hole proceed so deep as the stratum 4 of the former. It is evident, that, by this method of procedure, neither the coal nor any other of the strata can be passed over, as the last hole is always bored down to that stratum which was nearest the surface in the former hole.

The purposes for which boring is used are numerous, and some of them of the utmost importance in coalyards. In coalyards of great extent, although the coal be known to extend through the whole grounds, yet accidental turns, and other alterations in the dip, to which the coal is liable, render the boring of three or more holes necessary, to determine exactly to what point of the horizon it dips or inclines, before any capital operation for the winning of it can be undertaken; because a very small error in this may occasion the loss of a great part of the coal, or at least incur a double expense in recovering it.

Suppose A, B, C, D, fig. 5, to be part of an extensive field of coal, intended to be won or laid dry by a fire-engine; according to the course of the dip in adjoining coalyards, the point C is the place at which the engine should be erected, because the coal dips in direction of the line AC; consequently the level line would be in the direction CD; but this ought not to be trusted to. Admit two holes, 1, 2, be bored to the coal in the direction of the supposed dip, at 200 yards distance from each other, and a third hole 3 at 200 yards distance from each of them; suppose the coal is found, at the hole 1, to be 20 fathoms deep; at the hole 2, 10 fathoms deeper; but at the hole 3, only 8 fathoms deeper than at 1. Then to find the true level line and dip of the coal, say, As 10 fathoms the dip from 1 to 2, is to 200 yards the distance; fo is 8 fathoms, the dip from 1 to 3, to 160 yards, the distance from one on the line 1, 2, to a, the point upon a level with the hole 3. Again say, As 8 fathoms, the dip from 1 to 3, is to 200 yards the distance; fo is 10 fathoms, the dip from 1 to 2, to 250 yards, the distance from 1, in direction of the line 1, 3, to b, the point upon a level with the hole 2. Then let fall the perpendicular r, e, which will be the true direction of the dip of the coal, instead of the supposed line AC; and by drawing E D, and D F, parallel to the other lines, the angle D, and no other place, is the deepest part of the coal, and the place where the engine should be erected. If it had been erected at the angle C, the level line would have gone in the direction c b, by which means about one third part of the field of coal would have been below the level of the engine, and perhaps lost, without another engine was erected at D.

Boring not only shows the depth at which the coal lies, but its exact thickness; its hardness; its quality, whether close burning or open burning, and whether any foul mixture in it or not; also the thickness, hardness, and other circumstances of all the strata bored through; and from the quantity of water met with in the boring, some judgment may be formed of the size of an engine capable of drawing it, where an engine is necessary. When holes are to be bored for these purposes, they may be fixed (as near as can be guessed) in such a situation from each other, as to suit the places where pits are afterwards to be sunk; by which means most of the expense may be saved, as these pits would otherwise require to be bored, when sinking, to discharge their water into the mine below. There are many other uses to which boring is applied, as will be explained hereafter.

For these reasons, boring is greatly practised in England, and is brought to great perfection; and as the operation is generally entrusted to a man of integrity, who makes it his profession, the accounts given by him of the thickness and other circumstances of the strata, are the most accurate imaginable, and are trusted to with the greatest confidence; for as very few gentlemen choose to take a lease of a new coalyard which has not been sufficiently explored by boring, it is necessary the accounts should be faithful, being the only rule to guide the landlord in letting his coal, and the tenant in taking it. In Scotland it is not so generally practised; nor are there any men of character who are professed borers, that operation being commonly left to any common workman; whence it happens that it never has been in any esteem, the accounts given by them being so imperfect and equivocal as not to merit any confidence.

The tools or instruments used in boring are very simple. The boring rods are made of iron from 3 to 4 feet long, and about one inch and a half square, with a foree at each end, by which they are screwed together, and other rods added as the hole increases in depth. The chisel is about 18 inches long, and two and a half broad at the end, which being screwed on at the lower end of the rods, and a piece timber put through an eye at the upper end, they are prepared for work. The operation is performed by lifting them up a little, and letting them fall again, at the same time turning them a little round; by a continuance of which motions, a round hole is fretted or worn through the hardest strata. When the chisel is blunt, it is taken out, and a scooped instrument called a twimble put on in its stead; by which the dust or pulverised matter which was worn off the stratum in the last operation is brought up. By this substance, the borers know exactly the nature of the stratum they they are boring in; and by any alteration in the working of the rods (which they are sensible of by handling them), they perceive the least variation of the strata. The principal part of the art depends upon keeping the hole clean, and observing every variation of the strata with care and attention.

The established price of boring in England is 5s. per fathom for the first five fathoms, 10s. per fathom for the next five fathoms, and 15s. per fathom for the next five fathoms; and so continually increasing 5s. per fathom at the end of every five fathoms; the borer finding all kinds of boring instruments, and taking his chance of the hardness of the strata, except above one foot in thickness of which occur, when the former price ceases, and he is paid per day.

It is exceedingly uncommon to meet with a stratum of coal which is naturally dry, or whose subterranean springs or feeders of water are so very small as to require no other means than the labour of men to draw off or conduct them away; for it most commonly happens, that the stratum of coal, and the other strata adjacent, abound so much in feeders of water, that before access can be had to the coal, some other methods must be pursued to drain or conduct away these feeders; therefore, after the deepest part of the coal is discovered, the next consideration is of the best method of draining it, or, in the miner's language, of winning the coal.

If the coal lies in such an elevated situation, that a part of it can be drained by a level brought up from the lower grounds, then that will be the most natural method; but whether it be the most proper or not, depends upon certain circumstances. If the situation of the ground be such, that the level would be of a great length, or have to come through very hard strata, and the quantity of coal it would drain, or the profits expected to be produced by that coal, should be inadequate to the expense of carrying it up; in such case some other method of winning might be more proper. Or suppose, in another case, it be found, that a level can be had to a coalyery, which will cost £1,000, and require five years to bring it up to the coal, and that it will drain 32 acres of coal when completed; yet if it be found that a fire engine, or some other machine, can be erected on that coalyery, for the same sum of money, in one year, which will drain 50 acres of the same coal, then this last would be a more proper method than the level; because four years profit would be received by this method before any could come in by the other; and after the 30 acres drained by the level is all wrought, a machine of some kind would nevertheless be necessary to drain the remaining 20 acres; so that erecting a machine at first would be on all accounts the most advisable.

Where a level can be drove, in a reasonable time, and at an adequate expense, to drain a sufficient tract of coal, it is then the most eligible method of winning; because the charge of upholding it is generally less than that of upholding fire-engines or other machines.

If a level is judged properest after consideration of every necessary circumstance, it may be begun at the place appointed in the manner of an open ditch, about three feet wide, and carried forward until it be about six or seven feet deep from the surface, taking care to secure the bottom and sides by timber-work or building; after which it may be continued in the manner of a mine about three feet wide, and three feet and a half high, through the solid strata, taking care all along to keep the bottom upon a level, and to secure the roof, sides, and bottom, by timber or building, in all places where the strata are not strong enough to support the incumbent weight, or where they are liable to decay by their exposure to the fresh air. If the mine has to go a very long way before it reach the coal, it may be necessary to sink a small pit, for the convenience of taking out the stones and rubbish produced in working the mine, as well as to supply fresh air to the workmen; and if the air should afterwards turn damp, then square wooden pipes made of dales closely jointed (commonly called air-boxes), may be fixed in the upper part of the mine, from the pit-bottom all the way to the end of the mine, which will cause a sufficient circulation of fresh air for the workmen; perhaps in a great length it will be found proper to sink another or more pits upon the mine, and by proceeding in this manner it may be carried forward until it arrive at the coal; and after driving a mine in the coal a few yards to one side, the first coal-pit may be sunk.

If a level is found impracticable, or for particular reasons unadvisable; then a fire-engine*, or some other machine, will be necessary, which should be fixed upon the deepest part of the coal, or at least far enough towards the dip as will drain a sufficient extent of coal, to continue for the time intended to work the coalyery; and whether a fire-engine, or any other machine, is used, it will be of great advantage to have a partial level brought up to the engine-pit, if the situation of the ground will admit it at a small charge, in order to receive and convey away the water without drawing it too high as to the surface; for if the pit was 70 fathoms deep to the coal, and if there was a partial level, which received the water five fathoms only below the surface, the engine by this means would be enabled to draw a sixth part more water than without it; and if there were any feeders of water in the pit above this level, they might be conveyed into it, where they would be discharged without being drawn by the engine.

The engine-pit may be from seven to nine feet wide; and whether it be circular, oval, or of any other form, is not very material, provided it be sufficiently strong, though a circular form is most generally approved. If any feeders of water are met with a few fathoms from the surface, it will be proper to make a circular or spiral cutting about one foot deep, and a little hollowed in the bottom, round the circumference of the pit, in order to receive and conduct the water down, without flying over the pit and incommoding the workmen. If the strata are of so tender or friable a nature as not to bear this operation, or if the water leaks through them, then it will be necessary to insert in the forementioned cutting a circular piece of timber called a crib, hollowed in the same manner to collect the water; and a second may be inserted two or three yards below the first, with a sloping notch down the wall or side of the pit, to convey the water from the former into it; proceeding by some of these methods until the pit is sunk 15 or 20 fathoms; at which place it would be proper to fix a cistern. C O A

Coalery cistern or reservoir, for the first or upper set of pumps to stand in; for if the pit be 30 fathoms as supposed, it would be too great a length for the pumps to be all in one set from bottom to top; therefore, if any extraordinary feeders are met with, between 15 and 20 fathoms deep, it would be best to fix the cistern where it may receive them, and prevent their descending to the bottom; observing that the upper set of pumps be so much larger than the lower one, as the additional feeders may require; or if there are no additional feeders, it ought then to be a little smaller.

After the upper cistern is fixed, the operation may be pursued by the other set of pumps in much the same manner as has been described, until the pit is sunk to the coal; which being done, it would be proper to sink it six or eight feet deeper, and to work some coal out from the dip side of the pit, to make room for a large quantity of water to collect, without incommodeing the coal-pits when the engine is not working.

It would exceed the proper bounds of this article, to enumerate all the accidents to which engine-pits are liable in sinking; we shall therefore only recite a few which seem important.

If a quicksand happen to lie above the solid strata, next the surface, it may be got through by digging the pit of such a width at the top (allowing for the natural slope or running of the sand) as to have the proper size of the pit on the uppermost solid stratum; where fixing a wooden frame or tube as the timberwork of the pit, and covering it round on the outside with wrought clay up to the top, the sand may again be thrown into the excavation round the tube, and levelled with the surface.

If the quicksand should happen to lie at a considerable depth between the clay and solid strata, then a strong tube of timber closely jointed and fitted with iron, of such a diameter as the pit will admit, may be let down into it; and by fixing a great weight upon the top, and by working out the sand, it may be made to sink gradually, until it come to the rock or other solid stratum below; and when all the sand is got out, if it be lightly calked and secured it will be sufficient.

It sometimes happens, that a stratum of soft matter, lying between two hard solid ones, produces so large a quantity of water as greatly to incommode the operations. In such a case, a frame-work of plank, strengthened with cribs and closely calked, will stop back the whole or the greatest part of it, provided the two strata which include it are of a close texture; or let an excavation of about two feet be made in the soft stratum, quite round the circumference of the pit; and let that be filled close up between the hard strata, with pieces of dry fir-timber about ten inches square inserted endwise, and afterwards as many wooden wedges driven into them as they can be made to receive; if this be well finished, little or no water will find a passage through it.

It rarely happens that any suffocating damp or foul air is met with in an engine-pit; the falling of water, and the working of the pumps, generally calling a sufficient circulation of fresh air. But that kind of combustible vapour, or inflammable air, which will catch fire at a candle is often met with. It proceeds from the partings, backs, and cutters, of the solid strata, exhaling from some in an insensible manner, whilst Coalery, from others it blows with as great impetuosity as a pair of bellows. When this inflammable air is permitted to accumulate, it becomes dangerous by taking fire, and burning or destroying the workmen, and sometimes by its explosion will blow the timber out of the pit, and do considerable damage. If a considerable supply of fresh air is forced down the pit by airboxes and a ventilator, or by dividing the pit into two by a close partition of deals from top to bottom, or by any other means, it will be driven out, or so weakened, that it will be of no dangerous consequence; or when the inflammable air is very strong, it may be safely carried off by making a close sheathing or lining of thin deals quite round the circumference of the pit, from the top of the solid strata to the bottom, and lengthening it as the pit is sunk, leaving a small vacancy behind the sheathing; when the combustible matter, which exhales from the strata, being confined behind these deals, may be vented by one or two small leaden pipes carried from the sheathing to the surface; so that very little of it can transpire into the area of the pit. If a candle be applied to the orifice of the pipe at the surface, the inflammable air will instantly take fire, and continue burning like an oil-lamp until it be extinguished by some external cause. Upon the whole, every method should be used to make the pit as strong in every part, and to keep it as dry as possible; and whenever any accident happens, it should be as expeditiously and thoroughly repaired as possible, before any other operation be proceeded in, lest an additional one follow, which would more than double the difficulty of repairing it.

The first operations, after sinking the engine-pit, are the working or driving a mine in the coal, and sinking the first coal-pit. The situation of the first coal-pit should be a little to the rise of the engine-pit, that the water which collects there may not obstruct the working of the coals every time the engine stops; and it should not exceed the distance of 20, 30, or 40 yards; because when the first mine has to be driven a long way, it becomes both difficult and expensive. If there be not a sufficient circulation of fresh air in the mine, it may be supplied by the before described airboxes and a ventilator, until it arrive below the intended coal pit, when the pit may be bored and sunk to the coal, in the manner before mentioned.

After the pit is thus got down to the coal, the next consideration should be of the best method of working it. The most general practice in Scotland is to excavate and take away a part only of the stratum of coal in the first working of the pit, leaving the other part as pillars for supporting the roof; and after the coal is wrought in this manner to such a distance from the pit as intended, then these pillars, or so many of them as can be got, are taken out by a second working, and the roof and other solid strata above permitted to fall down and fill up the excavation. The quantity of coal wrought away, and the size of the pillars left in the first working, is proportioned to the hardness and strength of the coal and other strata adjacent, compared with the incumbent weight of the superior strata.

The same mode of working is pursued in most parts of England, differing only as the circumstances of the coalery. coalery may require: for the English coal, particularly in the northern counties, being of a fine tender texture, and of the close-burning kind, and also the roof and pavement of the coal in general not so strong as in Scotland, they are obliged to leave a larger proportion of coal in the pillars for supporting the roof, during the first time of working; and, in the second working, as many of these pillars are wrought away as can be got with safety.

The Scots coal in general being very hard, and of the open-burning kind, it is necessary to work it in such a manner as to produce as many great coals as possible, which is best effected by taking away as high a proportion of the coal as circumstances will allow in the first working; on the contrary, the English coal being very tender cannot possibly be wrought large, nor is it of much importance how small they are, being of so rich a quality; so that a larger proportion may be left in pillars in this coal than could with propriety be done in the other; and, when all circumstances are considered, each method seems well adapted to the different purposes intended.

The ancient method of working was, to work away as much of the coal as could be got with safety at one working only: by which means the pillars were left so small as to be crushed by the weight of the superior strata, and entirely lost. As great quantities of coals were lost by this method, it is now generally exploded, and the former adopted in its place; by which a much larger quantity of coal is obtained from the same extent of ground, and at a much less expense in the end.

The exact proportion of coal proper to be wrought away, and to be left in pillars at the first working, may be judged of by a comparison of the circumstances before mentioned. If the roof and pavement are both strong, as well as the coal, and the pit about 30 fathoms deep, then two-thirds, or probably three-fourths, may be taken away at the first working, and one-third or one-fourth left in pillars. If both roof and pavement be soft or tender, then a larger proportion must be left in pillars, probably one-third or near one-half; and in all cases the hardness or strength of the coal must be considered. If tender, it will require a larger pillar than hard coal; because, by being exposed to the air after the first working, a part of it will moulder and fall off, by which it will lose much of its solidity and resistance.

The proportion to be wrought away and left in pillars being determined, the next proper step is to fix upon such dimensions of the pillars to be left, and of the excavations from which the coal is to be taken away, as may produce that proportion. In order to form a just idea of which, see a plan of part of a pit's workings (fig. 6.), supposed to be at the depth of 30 fathoms, and the coal having a moderate rise. A, represents the engine-pit; B, the coal-pit; A a B, the mine from the former to the latter; B C, the first working or excavation made from the coal-pit, commonly called the winning mine or winning headway, nine feet wide; b b b b, &c., the workings called rooms, turned off at right angles from the others, of the width of 12 feet; c c c c, &c., the workings called throughers or thrilings, 9 feet wide, wrought through at right angles from one room to another; d d d, &c., the pillars of coal left at the first working for supporting the roof, 18 feet long and 12 feet broad; DD, two large pillars of coal near the pit bottom, 15 or 20 yards long, and 10 or 15 broad, to support the pit, and prevent its being damaged by the roof falling in; ee, the level mine wrought in the coal from the engine pit bottom, 4 or five feet wide; ff, &c., large pillars of coal left next the level, to secure it from any damage by the roof falling in; gg, a dike which depresseth the coal, 1 fathom; bb, &c., large pillars and barriers of coal left unwrought, adjoining to the dike where the roof is tender, to prevent its falling down. The coal taken out by the first working in this pit is supposed to be one-third of the whole; and allowing the rooms 12 feet wide, and the thrilings 9 feet wide, then the pillars will require to be 12 feet wide and 18 feet long; for if one pillar be in a certain proportion to its adjoining room and thriling, the whole number of pillars will be in the same proportion to the whole number of rooms and thrilings in the pit. Suppose A B C D, (fig. 7.), to be a pillar of coal 18 feet long and 12 feet broad, its area will be 216 square feet; A C H E, the adjoining thriling, 12 feet by 9 feet, and its area 108 square feet; B A E F G, the adjoining room, 27 feet long and 12 feet broad, and its area 324 square feet; which added to 108 gives 432 square feet, or two-thirds wrought, and 216 square feet left, or one-third of the whole area F G H D.

It is proper to observe, that in the prosecution of the workings, the rooms to the right of the winning headway should be opposite to the pillars on the left; and the first, third, and fifth pillar, or the second, fourth, and sixth, adjoining to the said headway, should be of such a length as to overlay the adjoining thrilings; as, in the plan, the pillar 2 overlays the thrilings 1 and 3; and the pillar 4, overlays the thrilings 3 and 5; this will effectually support the roof of the main road B C, and will bring the other pillars into their regular order, by which means each pillar will be opposite to two thrilings. Also a larger proportion of coal than common should be left in all places which are intended to be kept open after the second working; such as the pit-bottoms, air-courses, roads, and water-courses, or where the roof is tender, as it generally is near dikes, hitches, and troubles; and if the roof should continue tender for a considerable space, it will perhaps be found proper to leave a few inches of coal adhering to the roof, which, together with a few props of timber fixed under it, may support it effectually for a long time. The level mine ee, and the winning headway B C, should be wrought forward a considerable length before the other rooms, in order to be drove through any dikes that might interpose; otherwise the progress of the workings might probably be stopped a considerable time, waiting until a course of new rooms were procured on the other side of the dike. Suppose the dike gg, fig. 6., to depress the coal six feet or one fathom, and that it rises in the same manner on the under side of the dike as it does on the upper side; in such a case, the only remedy would be to work or drive a level mine through the strata of stone from the engine-level at e over the dike, until it intersect the coal at i; and from thence to drive a new level mine in the coal at ii, and a new winning headway i k. In order to gain a new set of rooms, rooms, and to supply fresh air to this new operation, a small mine might be drove from the room b, and a hole sunk down upon the level room ii; therefore, if the level mine ee was not drove so far forward as to have all these operations completed before the rooms and other workings were intercepted by the dike, the working of the pit might cease until these new places were ready.

If there be two or three strata or seams of coal in the same pit (as there often are) having only a stratum of a few feet thick lying between them, it is then material to observe, that every pillar in the second seam be placed immediately below one in the first, and every pillar in the third seam below one in the second; and in such a situation the upper stratum of coal ought to be first wrought, or else all the three together: for it would be unsafe to work the lower one first, lest the roof should break, and damage those lying above.

It sometimes becomes necessary to work the coal lying to the dip of the engine or the level; which coal is consequently drowned with water, and must therefore be drained by some means before it can be wrought. If the quantity of water proceeding from it be inconsiderable, it may then be drained by small pumps laid upon the pavement of the coal, and wrought by men or horses, to raise the water up to the level of the engine-pit bottom: or if the feeders of water be more considerable, and the situation be suitable, the working rod of these pumps might be connected with those in the engine-pit; by which means the water would be raised up to the level: but if the quantity of water be very great; or if, from other circumstances, these methods may not be applicable; then the engine-pit may be sunk as deep below the coal as may be necessary, and a level stone mine drove from its bottom to the dip of the strata, until it intersect the stratum of coal, from whence a new level mine might be worked, which would effectually drain it. Suppose A B, fig. 8, to be a section of the engine-pit; BC, the coal drained by the engine; BD, the coal to the dip of the engine intended to be drained; then if the engine-pit be sunk deeper to E, a stone mine may be wrought in the direction ED, until it intersect the coal at D, by which the water will have a free passage to the engine, and the coal will be drained.

If there be another stratum of coal lying at such a depth below the first as the engine-pit is intended to be sunk to, the upper seam may in some situations be conveniently drained, by driving a mine in the lower seam of coal from E to F; and another in the upper one from B to D; and by boring a hole from D to F, the water will descend to F, and, filling the mine EF, rise up to the engine-pit bottom at E, which is upon a level with D.

Whenever it is judged necessary to work the pillars, regard must be had to the nature of the roof. If the roof is tender, a narrow room may be wrought through the pillar from one end to the other, leaving only a shell of coal on each side for supporting the roof the time of working. Suppose ABCD, fig. 7, to be a pillar of coal 18 feet long and 12 feet broad; if the roof is not strong, the room 1, 2, 3, 4, of eight feet wide, may be wrought up through that pillar, leaving a shell of two feet thick on each side; and if it can be safely done, a part of these shells may also be wrought away, by working two places through them as at 5 and 6. By this means very little of the coal will be lost; for two-thirds of the whole being obtained by the first working, and above two-thirds of the pillar by the second working, the loss upon the whole would not exceed one-tenth; but it may be observed, that some pillars will not produce to great a proportion, and perhaps others cannot be wrought at all; so that, upon the whole, there may be about one-eighth, one-seventh, or in some situations one-sixth part of the coal lost. If the root be hard and strong, then as much coal may be wrought off each side and each end of the pillar as can be done with safety, leaving only a small piece standing in the middle; and when the roof is very strong, sometimes several pillars may be taken entirely out, without any loss of coal: and in general this last method is attended with less loss, and produces larger coals, than the former. In all cases it is proper to begin working those pillars first which lie farthest from the pit bottom, and to proceed working them regularly away towards the pit; but if there be a great number of pillars to the dip of the pit, it is the safest method to work them out before those to the rise of the pit are begun with.

There is no great difference in the weight of different kinds of coals, the lightest being about 74 pounds avoirdupois, and the heaviest about 79 pounds the cubic foot; but the most usual weight is 75 pounds the foot, which is 18 hundred weight and 9 pounds the cubic yard. The statute chaldar is 53 hundred weight; or when measured is as follows: 268.8 cubic inches to the Winchester gallon; 4½ gallons to the coal peck, about 3 pounds weight; 8 coal pecks to the boll, about 247½ pounds; and 24 bolls to the chaldar, of 53 hundred weight. If one coal measuring exactly a cubic yard (nearly equal to 5 bolls) be broken into pieces of moderate size, it will measure seven coal bolls and a half. If broken very small, it will measure 9 bolls; which shows, that the proportion of the weight to the measure depends upon the size of the coals; therefore accounting by weight is the most rational method.

A Table of the weight and quantity of coal contained in one acre Scots measure, allowing one sixth part to be lost below ground, in seams of the following thicknesses.

| Thickness of coal | Weight in tuns | Quantity in chaldars | |-------------------|---------------|---------------------| | Feet Inches | | | | 2 | 3068 | 1158 | | 2 | 3835 | 1447 | | 3 | 4602 | 1736 | | 3 | 5369 | 2025 | | 4 | 6136 | 2314 | | 4 | 6903 | 2603 | | 5 | 7670 | 2892 | | 5 | 8437 | 3181 | | 6 | 9204 | 3470 |

We shall next mention some of the various methods of bringing the coals from the rooms and other workings to the pit bottom. Where the stratum of coal is of a sufficient thickness, and has a moderate rise and dip, the coals are most advantageously brought out by horses, who draw out the coals in a tub or basket placed... ced upon a sledges: a horse by this means will bring out from four to eight hundred weight of coals at once, according to the quantity of the ascent or descent. In some coaleries they have access to the workings by a mine made for them, sloping down from the surface of the earth to the coal; and where that convenience is wanting, they are bound into a net, and lowered down the pit. If the coal be not of such a height as to admit horses, and has a moderate rise like the last, then men are employed to bring out the coals: they usually draw a basket of four or five hundred weight of coals, fixed upon a small four-wheeled carriage. There are some situations in which neither horses nor men can be properly used; particularly where the coal has a great degree of declivity, or where many steps occur: in such a case the coals are sent brought out by women called bearers, who carry them in a kind of basket upon their backs, usually a hundred, or a hundred weight and a half, at once.

When the coals are brought to the pit bottom, the baskets are then hooked on to a chain, and drawn up the pit by a rope to the surface, which is best effected by a machine called a gin, wrought by horses. There are other kinds of gins for drawing coals, some wrought by water, others by the vibrating lever of a fire-engine; but either of these last is only convenient in some particular situations, those wrought by horses being in most general use. After the coals are got to the surface, they are drawn a small distance from the pit, and laid in separate heaps: the largest coals in one heap, the smaller pieces called chews in another, and the culm or pan-coal in a separate place.

There is an accident of a very dangerous nature to which all coaleries are liable, and which has been the ruin of several: it is called a crush, or a rift. When the pillars of coal are left so small as to fail, or yield under the weight of the superior strata; or when the pavement of the coal is so soft as to permit the pillars to sink into it, which sometimes happens by the great weight that lies upon them; in either case the solid stratum above the coal breaks and falls in, crushes the pillar to pieces, and clothe up a great extent of the workings, or probably the whole coaly. As such an accident seldom comes on suddenly, if it be perceived in the beginning, it may sometimes be stopped by building large pillars of stone amongst the coal pillars; but if it has already made some progress, then the best method is to work away as many of the coal pillars adjoining to the crush as may be sufficient to let the roof fall freely down; and if it makes a breach of the solid strata from the coal up to the surface, it will very probably prevent the crush from proceeding any farther in that part of the coaly. If the crush begins in the rise part of the coaly, it is more difficult to stop it from proceeding to the dip, than it is to stop it from going to the rise when it begins in a contrary part.

Another circumstance proper to be taken notice of is the foul or adulterated air so often troublesome in coaleries. Of this there are two kinds: the black damp or stony, which is of a suffocating nature; and the inflammable or combustible damp. Without staying to inquire, in this place, into the origin and effects of these damps, it may be sufficient to observe, that, in whatever part of any coaly a constant supply or a circulation of fresh air is wanting, there some of these damps exist, accumulate in a body, and become noxious or fatal: and whenever there is a good circulation of fresh air, they cannot accumulate, being mixed with and carried away by the stream of air as fast as they generate or exhale from the strata. Upon these principles are founded the several methods of ventilating a coaly. Suppose the workings of the pits A and B (fig. 6.) to be obnoxious to the inflammable damps; if the communication was open betwixt the two pits, the air which went down the pit A would proceed immediately along the mine a, and ascend out of the pit B; for it naturally takes the nearest direction: so that the air in all the workings would be stagnant; and they would be utterly inaccessible from the accumulation of the combustible damp. In order to expel this, the air must be made to circulate through all the different rooms by means of collateral aircourses made in this manner: The passage or mine a must be closed up or flopped by a partition of deals, or by a wall built with bricks or stones, to prevent the air passing that way. This building is called a flopping. There must also be floppings made in the thrilings 1 1 1, &c. betwixt the pillars f f, &c. which will direct the air up the mine e e, until it arrive at the innermost thriling z, which is to be left open for its passage. There must also be floppings made at the side of the mine a at m m, and on both sides of the main headway BC at b b, &c. then returning to the innermost thriling z, proceed to the third row of pillars, and build up the thrilings z z, &c. leaving open the thriling 3 for a passage for the air; and proceeding on to the fifth row of pillars, build up in the same manner the floppings 3 3, &c. leaving open 4 for an air course: and by proceeding in this manner to flop up the thrilings or passages in every other row of pillars, the current of fresh air will circulate through and ventilate the whole workings, in the direction pointed to by the small arrows in the plan, clearing away all the damps and noxious vapours that may generate. When it is arrived at C, it is conducted across the main headway, and carried through the other part of the pit's workings in the same manner, until it return through n n to the pit B, where it ascends; and as the rooms advance farther, other floppings are regularly made.

In some of these floppings, on the sides of the main headway, there must be doors to admit a passage for the bringing out of the coals from the rooms to the pit, as at 5 5: these doors must be constantly shut, except at the time of passing through them.

There are other methods of disposing the floppings so as to ventilate the pit; but none which will so effectually disperse the damps as that described above. If the damps are not very abundant, then the course of floppings 1 1, &c. in the level mine, and the others at b b, &c. in the main headway, without any others, may perhaps be sufficient to keep the pit clear. If at any time the circulation of the fresh air is not brisk enough, then a large lamp of fire may be placed at the bottom of the pit B, which, by rarefying the air there, will make a quicker circulation.

Most of the larger coaleries send their coals to the leading ships for the coaling trade or exportation; and, as the quantity is generally very large, it would take a greater number of carts than could conveniently be obtained at all times to carry them; besides the considerable expense of Coalery, of that manner of carriage: they therefore generally use waggons, for carrying them along waggon-ways, laid with timber; by which means one horse will draw from two to three tons at a time, when in a cart not above half a ton could be drawn.

The first thing to be done in making a waggon-way is to level the ground in such a manner as to take off all sudden ascents and descents: to effect which, it is sometimes necessary to cut through hills, and to raise an embankment to carry the road through hollows. The road should be formed about 12 feet wide; and no part should have a greater descent than of one yard perpendicular in 10 of a horizontal line, nor a greater ascent than one yard in 30. After the road is formed, pieces of timber, about five feet long and six inches diameter, called sleepers, are laid across it, being 18 or 24 inches distant from each other. Upon these sleepers other pieces of timber, called rails, of four or five inches square, are laid in a lateral direction, four feet distant from each other, for the waggon-wheels to run upon; which being firmly pinned to the sleepers, the road may then be filled with gravel and finished.

The waggons have four wheels, either made of solid wood or of cast iron. The body of the carriage is longer and wider at the top than at the bottom; and usually has a kind of trap-door at the bottom, which, being loosed, permits the coals to run out without any trouble. The size of a waggon to carry 50 hundred weight of coals is as follows:

| Feet | Inches | |------|--------| | Length of the top | 7 | 9 | | Breadth of the top | 5 | 0 | | Length of the bottom | 5 | 0 | | Breadth of the bottom | 2 | 6 | | Perpendicular height | 4 | 3 |

Where the pits are situated at some considerable distance from the harbour, it becomes necessary to have a store-house near the shipping place, where the coals may be lodged, until the lighters or ships are ready to take them in. The waggon-way should be made into the store-house, at such a height from the ground, as to permit the coals to run from the waggons down a spout into the vessels; or else to fall down into the store-house, as occasion may require.

This kind of store-house is well adapted to dispatch and saving expense: for a waggon-load of coals may be delivered either into the store-house or vessels instantly with very little trouble: and if the coals were exposed to the effects of the sun and rain, they would be greatly injured in their quality; but being lodged under cover of the store-house, they are preserved.