COLLIERY.

A colliery or coal-work is a place where coals are extracted or quarried out from the stratified masses below ground, and brought to the surface by means of machinery.

It is generally agreed that our cannel coal is the lapis ampelites of the Romans, though it seems to have been used by them only for making toys, bracelets, and the like. But of that common fuel which we denominate coals the native Romans were entirely ignorant. It is certain that coals are not, as some have imagined, the lapis obsidianus of Pliny, about which there have been great disputes; nor the gaģates or jet, which others, again, have taken for the lapis obsidianus, though the lightness and texture of the latter show plainly that it was neither stone nor coal. In fact, there are no beds of this mineral in the whole compass of Italy. The great line of it seems to sweep round the globe from north-east to south-west; ranging at no distance from the south-easterly parts of our island, as is generally imagined, and visiting Brabant and France, but yet avoiding Italy.

The primeval Britons, however, appear to have used coal; and in the precincts of Manchester particularly, which are furnished with an inexhaustible abundance of it, they could scarcely have remained ignorant of the combustible material around them. The currents there frequently bring down fragments of coal from the mountains; and in their long and winding course 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 in the sand 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 forty; and a quantity of slack was dug up along with them. These circumstances show that the coals had been lodged upon the spot before the road made by the Romans covered it. That ground being in the neighbourhood of Mancenion, ^[1. That is, “the place of tents an ancient British town, the site of which was the present Castlefield at Manchester. ] the Britons had there deposited 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 sand 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-gual, and among the Cornish in their holan, 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 probably first noticed by the skill, and opened by the labour, of the Britons, some time before the arrival of the Romans among 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, in preference to any others. The current of the Medlock, which washes the sides of them, bringing down specimens of the riches within, would 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 chief fuel of the nation. In the year 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, ten vessels of Welsh and two of common ale, sixty cart loads of wood and twelve of pit coal, where we see that the quantity of coal was only one cart load to five of wood. The latter naturally continued the principal [7:7:71]article of our fuel as long as the forests and thickets were ready at hand; and this they continued to be till a very late period. The first public notice of the former is stated 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 license to dig coals; and the first statute relating to this article was the 9th Henry V. cap. 10, ordaining all keels in the port of Newcastle to be measured by commissioners before carriage of coals, on pain of forfeiture. But they were not brought into common use till the reign of Charles I. and were then sold for about seventeen shillings a chaldron.^[2. Campbell’s Political Survey. ] In some years after the restoration, there were about 200,000 chaldrons burnt in London; in 1670 about 270,000 chaldrons; at the revolution the consumption was upwards of 300,000 chaldrons; and at present 1,600,000 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 a considerable quantity both from England and from Scotland.

The most remarkable colliery or coal-work that we have ever had in this island was that wrought at Borrowstounness, under the sea. The strata of coal were found to stretch under the bed of the sea at this place, and the colliers had the courage to work these 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 quay, 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 drawn out upon the shore by an engine moved by water, that raised it forty fathoms. This coal-pit continued to be wrought many years, to the great profit of the owners, and the wonder of all who saw it; but at last an unexpected high tide destroyed the whole at once, and the labourers, not having time to escape, perished in it. j There are several other countries in Europe which pos- sess considerable coal mines, as France, Liège, Germany, and Sweden; while, on the other side of the Atlantic Ocean, namely, in Newfoundland, Cape Breton, Canada, and some of the New England provinces, coal has been discovered and wrought. But in all these countries the coal is of a quality much inferior to the British, and entirely unfit to be used in many manufactures; so that they import coal from Britain for various manufactures.

The terrestrial matter which composes the solid parts of the earth is disposed in strata, beds, or layers, 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. And these strata consist of very different kinds of matter, such as freestone, limestone, metalstone or whinstone, coal, &c. as will be particularly specified in the sequel. Some of the strata are of 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 dusty matter betwixt them, called the parting, which renders them easily separable; or else only by the surfaces closely conjoined to each other, without any visible matter interposed betwixt them; yet the different substances of the strata are 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 do they make so effectual a parting, as the principal ones; and they are only met with in such strata as are not of a 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 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 a direction oblique or perpendicular 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. Sometimes they have a kind of thin partition of dusty or soft matter in them, and sometimes they have 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 men-’ tioned, 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, I, 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 perpendicularly.

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

Dikes arc 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 having 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 reached, 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 well 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[7:7:72] matter, different from that of the solid strata on each side of it. It is sometimes found charged 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 suppo⅞e 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 ten or twenty fathoms lower than on the other side, it is then said to be a dip-dike or doroncast-dike, or slip of ten or twenty fathoms to the eastward; or counting from the east side, it is then said to be a rise-dike or upeast of so many fathoms westward. If the strata on one side are not mueh 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, and so on.

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, cavities of which are filled with spar, the ores of iron, lead, vitriol, or other metallic or mineral matters; and it is pretty well known that all metallie veins are nothing else than what in the coal countries are called dikes, or slips, or faults.

The strata, as mentioned above, are generally found lying upon each other in the same order on one side of the dike as on the other, and nearly of the same thicknesses; appearing to have been originally a continuation of the same regular strata, and the dike only a breach made by some later accident, perpendicularly or obliquely through them, by which one part was 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 all the strata are, to a considerable distance on each side of the dike, in a kind of shattered condition, very tender, easily pervious to water, and debased greatly in their quality, while their inclination to the horizon is often altered.

Troubles may be denominated dikes of the smallest degree; for they are not a real breach, but only a tendency towards it, which has not taken full effect. The strata are generally altered by a trouble from their regular site to a different position. Where 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 increases or alters it to a contrary position: And a trouble has t*ιese effects upon the strata in common with dikes, that it greatly debases them from their original quality; that the partings are separated; that the backs and cutters are disjoined, and their regularity disordered; that the original cubic and prismatic figures of which the strata were composed are broken, and the dislocation filled with heterogeneous matter; and that 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 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 iii a perpendicular direction. But whatever degree of inclination the strata have to the horizon, they are generally found, if not interrupted by dikes, hitches, or troubles, to lie in the regular manner first 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, every considerable alteration in the dip is occasioned by the circumstances last mentioned.

To illustrate what has been said, see fig. 2, where a, b, c, d, &c. represent a course of strata lying upon each other, having a certain inclination to the horizon. AB is a downeast dike or slip, which depresses the strata obliquely to e,f, y, h, &c. lying upon each other in the same order, but altered in their inclination to the horizon. CD represents a clay or freestone dike or fault, where the strata are neither elevated nor depressed, but only broken off and removed to a certain distance. L’F represents a hitch, which breaks off and depresses the strata only a little, but alters their inclination to the horizon. GH 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 thickness, whilst others remain the same, consequently' they cannot be all parallel; yet this increase and diminution in thickness come 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 fifty, or even a hundred fathoms underneath, 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 contradieted by experience. If it was so, we should meet with dikes at the skirts of the hills, and by the sides of the valleys, and the sea-shore; but instead of this, we generally find the strata lying as uniformly regular under hills and valleys, and be-neath the bottom 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 irregùlarities are occasioned in the solid strata by dikes, or other slips and 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 the valley's, there the solid strata are exposed, and the dip, 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[7:7:73] of the solid strata, are equally applicable to the strata of coal as to those of stone or other matter.

All the strata of the coal formation do not lie or bear upon each other in any certain or invariable order. Though there be found the same kinds of strata in one colliery or district as in another, yet they may be of very different thickness. 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 ten or twenty times before we reach the principal stratum of coal.

In order to explain this, suppose the strata in the pit at A, fig· 3, to lie in the order a, b, c, &c. they may be so much altered in thickness, by reason of some of them increasing and others diminishing, at the distance of B, that they may be found there of very different thickness; or if they are examined in a pit at D, by reason of its lower situation, and the strata there not being a continuation of those in the other places, they may be very different both in their order and thickness, and yet of the same kinds.

Though they be thus found very different in one colliery or district from what they are found to be in another, with respect to thickness and the order in which they lie upon each other, yet we never meet with a stratum of any kind of matter that does not belong to some of those above described.

To illustrate how the various strata lie in some places, and how often the same stratum may occur betwixt the surface and the coal, we shall give the following example. The numbers in the left-hand column refer to the classes of strata before described, to which each belongs; the second column contains the names of the strata; and the four numeral columns to the right hand express the thickness of each stratum, in fathoms, yards, feet, and inches.

Example.
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In this instance the species of sandstone only occurs twice, post five times, whilst the shiver occurs no less than nine times.

To apply the foregoing observations to practice, suppose it were required to examine whether there was coal in a piece of ground adjoining to or in the neighbourhood of other collieries:

In the first place, it is proper to be informed, at some of the adjacent collieries, of the number and kinds of strata; the order in which they lie upon each other; to what point of the horizon, and in what quantity, they dip; and whether there be any dikes, hitches, or troubles, and in what course they stretch. Having learnt these circumstances, search in the ground under examination where the strata are exposed to view, and compare these strata with the other. If they be of the same kinds, and nearly correspond in order and thickness, and be lying in a regular manner, and agree by computation with the dip and rise, it may safely be concluded that the coal is there; and the depth of it may be judged of from the depth of the coal in the other colliery, below any particular stratum which is visible in this.

If the solid strata are not exposed to view, either in the hills or 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 colliery, and there is reason, from the dip and other circumstances, to believe that the ground to be examined has been stretched through, it may then be concluded that the coal is there, as well as these other strata.

Suppose a colliery is on the side of a hill at A, fig. 3, and you would search for 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 that they extend regularly from the first place to this, it is more than probable that 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 Ľ, 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, computing the quantity of ascent or rise of the coal in that distance, and comparing these together, it may be judged at what depth the coal will be found there, supposing that it lies regularly. Thus, suppose the coal at A eighty yards deep, the distance from A to E 500 yards, and that the coal rises one yard in ten of horizontal distance:
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Or suppose that the place at B is 500 yards the con-trary[7:7:74] 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,
[table]

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 depresses 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 upeast dike of ten fathoms or twenty yards towards B, then deduct twenty from fifty, the depth before computed, and there will remain thirty yards or fifteen 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 so considerable a distance from all other collieries that, by reason of the intervention of hills, valleys, unknown dikes, &c. the connection or relation of the strata with those of any other colliery 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 one; and a few general rules, founded on the foregoing observations, arid on conclusions drawn from them, will 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 is the most likely to contain those kinds of strata favourable to the production of coal; and consequently such part being found, it is the most advisable to begin with the examination of it.

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, is commonly composed of strata much harder than, 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 mountainous or champaign countries; and a country so situated, 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 such moderate rising grounds as those last described, are also very favourable to the production of coal, if the solid strata, and other circumstances in the higher grounds adjoining, be conformable; for it will scarcely be found, in such a situation, that the strata are favourable in the rising grounds on both sides of the plain, and not so in the space betwixt them. But though plains be in certain circumstances so favourable to the production of coal, yet it is often more difficult to be discovered in such a situation than in that before described; because the clay, soil, and other lax matter, brought off the higher grounds by rains and other accidents, have generally covered the surfaces of such plains to a considerable depth, which prevents the exploration of the solid strata there, unless they be exposed to view by digging, quarrying, or some such operation.

That part of the district which abounds with moderate hills and valleys being fixed upon as most proper to begin the examination at, the first step to be taken is to examine all places where the solid strata are exposed to view, which are called the crops of the strata, as in precipices, hollows, &c. tracing them as accurately and gradually as the circumstances will allow, from the uppermost stratum or highest part of the ground to the very undermost; and if they appear to be of the kinds before described, it will be proper to note in a memorandum book their different thicknesses, the order in which they lie upon each other, the point of the horizon to which they dip or incline, the quantity of that inclination, and whether they lie in a regular state or order. This should be done in every part of the ground where they can be seen, observing at the same time, that if a stratum can be found in one place which has a connection with some other in a second place, and if this other has a connection with another in a third place, &c. then, from these separate connections, the joint correspondence of the whole may be traced, and the strata which in some places are covered may be known by their correspondence with those which are exposed to view.

If by this means the crops of all the strata cannot be seen, which is often the case, and if no coal be discovered by its crop appearing at the surface, yet if the strata which have been viewed consist of those kinds before described, and are found lying in a regular order, it is sufficiently probable that coal may be in that part of the district, although it be concealed from the sight by the surface of the earth or by other matter. Therefore, at the same time that the crops of the strata are under examination, it will be proper to take notice of all such springs of water as seem to be of a mineral nature, particularly those known by the name of iron water, which precipitate a mud or sediment of the colour of rust or iron, having a strong astringent taste. Springs of this kind proceed originally from those strata which contain beds or balls of iron-ore; but by reason of the tenacity of the matter of those strata, the water only disengages itself slowly from them, descending into some more porous or open stratum below, where, gathering in a body, it runs out to the surface in small streamlets or rills. The stratum of coal is the most general reservoir of this water; for the ironstone being lodged in different kinds of shiver, and the coal commonly 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 ochery matter in the water, when it comes from a stratum of coal, is of a darker rusty colour than when it proceeds from any [7:7:75]other, and often brings with it particles and small pieces of coal; therefore, wherever these two circumstances concur in a number of these kinds 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, but 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. If a number of these kinds are situated 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, with 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 belonged 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 shiver or freestone, this is a concurrent proof that it has come only from a small distance. Though the two methods before mentioned 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, such a circumstance, when joined to the other two, amounts to little less than a moral certainty that a stratum of coal exists 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 is 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 perpendicularly down, in order to reach 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 inclosed betwixt two solid strata, the uppermost called the roof, and the undermost called the pavement, of the coal. In such situations therefore it becomes necessary, either to dig a new pit, or to work a mine forward until the stratum of coal be found included betwixt 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 others again, 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, this 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 a certain district, situated within a few miles of the sea or some navigable river, being examined, 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 reach the coal; next the method of clearing it from water, commonly called winning it; and then 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 that, from the appearance of the strata, 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 west towards A; but the ground being flat, and covered to a considerable depth with earth, Ac. 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 ten fathoms, and not finding coal, it will be better to bore a new hole than to proceed to a great depth in that place. Proceeding, therefore, as far to the eastward as B, where the stratum 1 of the first hole is computed to be ten or twelve 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 as far to the eastward as it may be computed that the stratum 4 of the second hole will be met with at the depth of ten or twelve fathoms, a new hole may be bored 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 [7:7:76]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 collieries. In collieries 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 a part of an extensive field of coal, intended to be won or laid dry by a steam-engine; according to the course of the dip in adjoining collieries, the point C is the place at which the engine should be erected, because the coal dips in the direction of the line AC, consequently the level line would be in the direction CD; but this ought not to be trusted to. Admit that two holes, 1, 2, are bored to the coal in the direction of the supposed dip, at two hundred yards distance from each other, and a third hole, 3, at two hundred yards distance from each of them: suppose the coal is found at the hole 1 to be twenty fathoms deep, and at the hole 2, ten fathoms deeper, but at the hole 3, only eight fathoms deeper than at 1: then, to find the true level line and dip of the coal, say, as ten fathoms, the dip from 1 to 2, are to two hundred yards, the distance, so are eight fathoms, the dip from 1 to 3, to one hundred and sixty yards, the distance from 1 on the line 1, 2, to a, the point upon a level with the hole 3; and again say, as eight fathoms, the dip from 1 to 3, are to two hundred yards, the distance, so are ten fathoms, the dip from 1 to 2, to two hundred and fifty 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 1, c, which will be the true direction of the dip of the coal, instead of the supposed line AC; and by drawing ED and DF 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, unless another engine was erected at D.

Boring not only shows the depth at which the coal lies, but its exact thickness, its hardness, and its quality, whether close burning or open burning, and whether any foul mixture is 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 nearly as can be guessed, in such situations 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 mire below. There are many other uses to which boring is applied, as will be explained hereafter.

For these reasons boring is much practised in England, and is brought to great perfection; and as the operation is generally intrusted 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 colliery which has not been sufficiently explored by boring, it is necessary that the account 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, that operation being commonly left to any common workman; whence it happens, that it never has been in any esteem, the accounts given by the mere operators 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 three to four feet long, and about one inch and a half square, with a screw at each end, by which they are screwed together, and other rods added, as the hole increases in depth. The chisel is about eighteen 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 of 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 wimble, put on in its stead, by which the dust or pulverized 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 are boring in; and by any alteration in the working of the rods, which they become sensible of by the handling, 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 was some time ago five shillings per fathom for the first five fathoms, ten shillings per fathom for the next five fathoms, and fifteen shillings per fathom for the next five fathoms; and so continually increasing five shillings per fathom at the end of every five fathoms, the borer finding all kinds of boring instruments; but if more than one foot in thickness of whin occur, 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 as to 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 great length, or have to run through very hard strata, and if 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 should be found that a level can be had to a colliery, which will cost L.2000, and require five years to bring it up to the coal, and that it will drain thirty acres of coal when completed; yet if it be found that a steam-engine, or some other machine, can be erected on that colliery for the same sum of money, in one year, which will drain fifty acres of the same coal, then this last would be a more proper method [7:7:77]than the level; because four years profit would be received by this method before any could come in by the other; and after the thirty acres drained by the level were all wrought, a machine of some kind would nevertheless be necessary to drain the remaining twenty acres; so that erecting a machine at first would be on all accounts the most advisable. . . .

Where a level can be driven in ä 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 steam-engines or other machines.

If, after consideration of every necessary circumstance, a level is judged the most proper, 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 be pushed 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 become damp, then square wooden pipes made of deals 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 other pits upon the mine, and by proceeding in this manner it may be carried forward until it arrive at the coal; and after driving the mine into 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 steam-engine, or some other machine, will be necessary, which should be fixed upon the deepest part of the coal, or at least so far towards the dip as will drain a sufficient extent of coal to continue for the time intended to work the colliery; but whether a steamengine 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 admit of it at a small charge, in order to receive and convey away the water, without drawing it so high as to the surface; for if the pit were thirty fathoms deep, and if there were a partial level which received the water five fathoms only below the surface, the engine by this means would be enabled to draw one sixth 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.

she 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 me 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 ater leaks through them, then it will be necessary to in sert in the cutting before mentioned 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 niche 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 fifteen or twenty fathoms, at which place it will be proper to fix a cistern or reservoir for the first or upper set of pumps to stand in: for if the pit be thirty 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 betwixt fifteen and twenty fathoms deep, it will 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 as much larger than the lower one as the additional feeders may require, or if there be no additional feeders, that it 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 incommoding 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 happens to lie above the solid strata next the surface, it may be got through by digging the pit of such a wideness 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 tub as the timber-work 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 tub, and levelled with the surface. If the quicksand should happen to lie at a considerable depth betwixt the clay and solid strata, then a strong tub of timber, closely jointed and shod 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 reaches 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 betwixt two hard and solid ones produces so large a quantity of water as greatly to incommode the operations. In such a case, a framework of plank, strengthened with cribs and closely calked, will keep back the whole or the greater part of it, provided the true 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 betwixt 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 fal ’ ing of water, and the working of the pumps, generally causing 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 from others it blows with as great [7:7:78] 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 it 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 air-boxes 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 twenty, thirty, or forty 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 air-boxes before described, and a ventilator, until it arrives below the intended, coal-pit, when the pit may be bored and sunk to the coal in the manner previously mentioned.

After the pit is thus sunk down to the coal, the next consideration should be 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 root; 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, are 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 colliery 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 being 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 done with safety.

The Scotch 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 large a proportion of the coal as circumstances will admit 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 thirty 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 and tender, then a larger portion must be left in pillars, probably one third or nearly 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 this, see a plan of part of a pit’s workings (fig. 6), supposed to be at the depth of thirty fathoms, and the coal having a moderate rise. A represents the engine-pit; B the coalpit; AαB the mine from the former to the latter; BC the first working or excavation made from the coal-pit, commonly called the winning mine or winning headway, nine feet wide; bbbb, &c. the workings called rooms, turned off at right angles from the others, of the width of twelve feet; cccc, &c. the workings called t’hroughers or thirlings, nine feet wide, wrought through at right angles from one room to another; ddd, &c. the pillars of coal left at the first working for supporting the roof, eighteen feet long and twelve feet broad; DD two large pillars of coal near the pit bottom, fifteen or twenty yards long, and ten or fifteen 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, four 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 depresses the coal, one fathom; ĩih, &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 to be twelve feet wide, and the thirlings nine feet wide, then the pillars will require to be twelve feet wide and eighteen feet long; for if one pillar be in a certain proportion to its adjoining room and thirling, the whole number of pillars will be in the same proportion to the. whole number of rooms and thirlings in the pit. Suppose ABCD (fig. 7) to be a pillar[7:7:79] of coal eighteen feet long and twelve feet broad, its area will be 216 square feet; ACHE the adjoining thirling, twelve feet by nine feet, and its area 108 square feet; BAEFG the adjoining room, twenty-seven feet long and twelve 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 FGHD.

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 thirlings, as in the plan the pillar 2 overlays the thirlings 1 and 3, and the pillar 4 overlays the thirlings 3 and 5. This will effectually support the roof of the main road BC, and will bring the other pillars into their regular order, by which means each pillar will be opposite to two thirlings. A larger proportion of coal than common should also 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 BC, should be wrought forward a considerable length before the other rooms, in order to be driven 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 ik. In order to gain a new set of rooms, and to supply fresh air to this new operation, a small mine might be driven from the room ħ, and a hole sunk down upon the level room it ; therefore, if the level mine ee was not driven 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 interposed betwixt them, it is then material to observe that every pillar in the second seam be placed immediately before 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 driven from its bottom to the dip of the strata, until it intersect the stratum of coal, from whence a new level mine might be wrought, which would effectually drain it. Suppose AB, 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 FD, 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 during the time of working. Suppose ABCD, fig. 7, to be a pillar of coal eighteen feet long and twelve 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 so great a proportion, and others perhaps cannot be wrought at all; so that, upon the whole, there may be about one sixth, one seventh, or, in some situations, but one eighth part of the coal lost. If the roof 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 bottom of the pit, 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 these out before those to the rise of the pit are commenced withal.

There is no great difference in the weight of different kinds of coals, the lightest being about seventy-four pounds avoirdupois, and the heaviest about seventy-nine pounds, the cubic foot; but the most usual weight is seventy-five pounds the foot, which is eighteen hundredweight and nine pounds the cubic yard. The statute chaldron is fifty-three hundredweight; or, when measured, is as follows: 268*8 cubic inches to the Winchester gallon; four and a half gallons to the coal peck, about three pounds weight; eight coal pecks to the boll, about 247^- pounds; and twenty-four bolls to the chaldron of fifty-three hundredweight. If one coal measuring exactly a cubic yard, and nearly equal to five bolls, be broken ùito pieces of a moderate[7:7:80] size, it will measure seven coal bolls and a half If broken very small it will measure nine 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 Scotch measure, allowing one sixth part to be lost below ground, in scams of the following thickness.
[table]

We shall next mention some of the various methods of bringing the coals from the rooms and other workings to the bottom of the pit. 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 upon a sledge. A horse by this means will bring out from four to eight hundredweight of coals at once, according to the quantity of ascent or descent. In some collieries 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 hundredweight 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 descent, or where many dikes occur. In such a case the coals are best brought out by women called bearers, who carry them in a kind of basket upon their backs, usually a hundredweight or a hundredweight and a half at once.

When the coals are brought to the bottom of the pit, the baskets are then hooked on to a chain, and drawn up the pit by a rope to the surface, which is commonly 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 steam-engine. After the coals are got to the surface, they are drawn a small distance from the pit, and laid in separate heaps; the larger 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 collieries are liable, and which has been the ruin of several; it is called a crush or a sit. 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 closes up a great extent of the workings, or probably the whole colliery. 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 colliery. If the crush begins in the rising part of the colliery, 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 collieries. Of this there are two kinds; the black damp or styth, 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 colliery a constant supply or circulation of fresh air is wanting, there some of these damps exist, accumulate in a volume, and become noxious or fatal; but 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 colliery. 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 air-courses made in this manner. The passage or mine a must be closed up or stopped 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 stopping. There must also be stoppings made in the thirlings 111, &c. between the pillars ι ∕y> &c. which will direct the air up the mine e, e, until it arrives at the innermost thirling 2, which is to be left open for its passage. There must also be stoppings made at the side of the mine a at m m, and on both sides of the main headway BC at bb, &c. ; then returning to the innermost thirling 2, proceed to the third row of pillars, and build up the thirlings 2 2, &c. leaving open the thirling 3 for a passage for the air; and proceeding on to the fifth rowof pillars, build up in the same manner the stoppings 3 3, &c. leaving open 4 for an air-course. And by proceeding in this manner to stop up the thirlings 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 returns through n n, to the pit B, where it ascends; and as the rooms advance farther, other stoppings are regularly made. In some of those stoppings 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 stoppings so as to ventilate the pit, but none which will so effectually disperse the damps as that above described. If the damps are not very abundant, then the course of stopping 111, &c. in the level mine, and the others at bbb, &c. in the main headway, without any others, may perhaps be sufficient[7:7:81] 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 occasion a quicker circulation.

Most of the larger collieries send their coals to the ships for the coasting 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 that manner of carriage; they therefore generally use waggons for carrying them along railways, laid with timber or iron, by which means one horse will draw from two to ten tons at a time, when, in a cart, not above one ton could be drawn.

The first thing to be done in making a railway of timber, 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 twelve feet wide, and no part should have a greater descent than one yard perpendicular in ten of a horizontal line, nor a greater ascent than one yard in thirty. After the road is formed, pieces of timber about six feet long and six inches diameter, called sleepers, are laid across it, being eighteen or twenty-four 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, permit^ the coals to run out without any trouble. The size of a waggon to carry fifty hundredweight of coals is as follows :—
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Railways were at first made with timber, as above described, but are now generally made with cast or bar iron rails, laid upon blocks of stone; for a particular account of which see Wood on Railways.

What is above described was the common method of winning and working coal forty years ago, and is yet in general use. We shall now describe improvements which have been made and adopted with success in many of the English and Scotch coal-mines.

What is generally called the winning of a colliery, is the draining of a field of coal, so as to render the several seams accessible, by pits to be sunk from the surface.

In order to determine the most eligible situation for a winning, it is requisite that the field of coal to be obtained by it should have been previously explored by the methods above stated.

Supposing the field of coal (see profile A, B, Plate CLXXIV. fig. 1) to have been explored, by the borings a,b,c, d, and the crop of the seams e, and that it is determined to win the tract of coal in the seams C, D, extending from the ravine at a, to the crop of the seams at e.

In this case an adit or day-level drift or mine, rf, is set in from the ravine near to a, and is carried forward in a direct line until it cuts the seam C at f This day-level drift also cuts the bore-hole b at∙f, by which the stratification from b to f is drained, and a coal-pit is then sunk upon the bore-hole bf, from the surface to the seam C, with great facility.

In prosecuting the working of the coal from the pit f, towards the bore-hole C, a downthrow slip-dike gg is met with, which depresses the seam C to E. The extent of this depression is ascertained by driving an horizontal stone-drift from where the seam C terminates at the dike g g to lι, and by putting down the bore-hole i.

The day-level drift is then continued from f till it cuts the seam at E; and by carrying it forward to the bore-hole C, another coal-pit, cj, is obtained, in the same manner as at b.

From j the working of the seam is carried on progressively until the upthrow slip-dike hk is met with. An horizontal drift is then extended from I to m, from which one boring is made upwards to the seam C, and another downwards to the seam D, by which the position of both seams is proved. The day-level drift may then be extended from the pit cj through the dike kk into the seam D to n, to open out the bore-hole d, on which another coal-pit may be sunk through the seam C to the seam D, which may also be wrought by the pit d n, as well as the scam C.

The workings in both scams may now be carried on from the pit d n till they encounter the whin dike o o, which must be set through by carrying a drift through it on the same line of ascent as the seam leading to it, as dikes of this description seldom alter the level of the strata which they intersect. From the whin dike the working of both seams may be carried on without further difficulty to the crop of the coal at e.

This tract of coal, or colliery, may now be supposed to be wrought to the utmost extent that is available, by the day-level winning, and that it is determined to win the coal lying below this level by a steam-engine.

An engine-pit, F G, is, therefore, sunk upon the day-level drift f and through the seam C to D, below which the pump-well or lodge H is dug. After the sinking of the engine-pit is completed, a drift is carried forward towards the rise of the seam to L, where it will cut the bore-hole bf, and allow the coal-pit to be sunk from y to L; and the dike g g having been already explored, the water-course, or engine-level drift, is carried forward from the lodge at H, till it cuts the lower seam D at K, and thence forward in the seam D till it cuts also the bore-hole cj and the upthrow dike lilι successively, by which the whole extent of the seam D from G, by K to k, is drained and wrought by the pits b andc, which have been sunk by the bore-holes discharging the water from them into the engine-level.

It will be readily seen by referring to the profile, that the engine lifts the water no higher than the day-level drift f, by which it is discharged from the pump at r into the day-lcvel drift, and thence into the ravine at a. The dip part of the upper seam C may also be won as far as S, by extending the engine level drift from the lodge II to S, as shown by the dotted lines.

This mode of winning collieries can, however, only be pursued where the localities of the situation render it eligible; but as it frequently happens that collieries arc to be won where the surface of the ground is so nearly horizontal as not to admit of any benefit being derived from a day-level drift, it is necessary in such cases to draw the water to the surface by one or more steam-engines, as the case may require.

It frequently happens in situations of this kind, as in the neighbourhood of Newcastle-upon-Tyne, that great difficulties are encountered in the sinking through quicksands and very large feeders of water, some of which have been ascertained to communicate with the river Tyne.

The quicksands lie at various depths from the surface, as low as thirty fathoms and upwards; but the largest [7:7:82]feeders of water are seldom met with at a greater depth than fifty fathoms. The quicksands vary much in thickness, as the feeders of water do in quantity; but a feeder which discharged nearly 4000 gallons per minute has been met with in one shaft. As it would be impracticable to draw such a quantity of water from the bottom of those deep mines, except at an expense which could not be afforded, they are always stopped back by what is called tubbing and wedging, which is done by fixing water-tight cylinders of wood or cast iron within the circumference of the shaft, so as completely to dam back the water, and prevent its falling to the bottom of the pit. In some eases water has been dammed back in this manner to the height of seventy fathoms, and at an expense of L.120 per fathom, or upwards. Quicksands are also passed through and dammed back by tubs or cylinders of wood or cast iron, which are generally lowered down by ropes from the top of the pit, until they pass through the sand, and rest on the solid strata below.

As the sinking of the pits under the above circumstances is attended with great expense and difficulty, no more are sunk than what may be barely necessary to work the destined part of coal below, and in some cases a whole colliery is wrought by one pit.

In situations of this kind, where the whole of the operations of the mine, as the drawing of coals and water, as well as the ventilation of the workings, are to be carried on by one pit, it follows that such pits must be made of large diameter, and divided into separate shafts.

They have, therefore, been sunk from nine to sixteen feet in diameter, and divided into two, three, and four separate shafts by brattice, or partitions of deal boards, according to the circumstances and extent of the mine.

Plate CLXXIV. fig. 2, represents a pit of nine feet diameter, which is divided by the brattice or partition α, b, into a coal shaft A, and an engine shaft B.

Fig. 3 represents a pit of sixteen feet diameter, divided by the partitions a, b, 'c, into two coal shafts AA, and an engine shaft B.

Fig. 4 represents a pit of sixteen feet diameter, divided into three coal shafts AAA, and an engine shaft B, by the partitions α, b, c, d.

In practice it has been found that the mode of dividing the shaft, as shown by fig. 2, is the most eligible.

Collieries have been wrought to a great extent by pits of this description; the workings have been sometimes carried to the distance of two miles from the bottom, and the height of the air-course has exceeded thirty miles. Several of the pits constructed in this manner in the Newcastle district exceed 100 fathoms in depth, and some are nearly 150 fathoms deep.

Most of these large double pits have powerful steam-engines upon them for pumping water; they are generally of Mr Watt’s construction, double power, and usually exceed 100 horses’ power, besides one or two more of the same construction for drawing coals, of from twenty to thirty horses’ power.

As the principal feeders of water lie near the surface, the pumping engine is generally erected when the sinking commences. The pumps, which are now invariably made of cast iron, are suspended by ropes, and lowered down by capstans as the sinking proceeds.

Bods of fir timber six or seven inches square, called ground-spears, are placed, according to the size of the pumps they have to bear, one on each side of the coluιnn or set of cast-iron pipes, to which they are firmly tied at every nine feet by cords called lashings. A five-fold block is fixed to the top of each ģround-spear, the tail-ropes or falls of which pass round capstans placed near the top of the pit, by which the column of cast-iron pipes in the pit can be raised or lowered at pleasure. A column of pipes, generally called a “set of pumps,” suspended in this way, is as steady as if it was firmly fixed in a frame of timber. Pumps of sixteen to eighteen inches diameter may be carried to the depth of fifty fathoms in this way, if necessary; but, in this ease, it is expedient to add a third pair of blocks.

It is, however, only in cases of necessity that columns of pipes of this length are suspended on ground-spears and ropes, as, if circumstances will permit, the column of pipes ought to be firmly fixed in a cistern at the depth of twenty-five or thirty fathoms; but in many cases no dry situation can be met with in which to place the cistern, till the pit is sunk below the level of the large top-feeders, and consequently below the tubbing, in which it has not yet been found practicable to fix a cistern.

While the pipes are suspended in the manner above described, they are called sinking sets; after they are fixed on cisterns they are called standing sets.

Fig. 5 represents the method of suspending cast-iron pipes for sinking, aa, The iron blocks and ground ropes, with their falls, óó, leading to the capstans placed in any convenient situation near the top of the pit.

dd, The iron UU’s which connect the blocks with the tops of the ground-spears ee. c, The hoggar-pump, generally made of fir staves, and fixed by an iron flange and bolts to the uppermost cast-iron pipe. Always when the increased depth of the pit requires an additional pipe, the hoggar∙pump is taken off, and put on the top of the new pipe again.

f, The hoggar or leathern case, which delivers the water into the laundry box.

y, The flexibility of the hoggar enables it to accommodate itself to the gradual lowering of the pipes as the depth of the pit increases.

∕z7z, The bottom rods which connect the ground-spears with the wind-bore of the pumps. The wings ii are east upon the wind bore, for the purpose of attaching the bottom rods to it by slots or bolts.

kkk, The lashings by which the pipes are fixed to the ground-spears.

m, The pump-rod, wrought by the engine.

n, The snore-holes of the pump, which are plugged up, or kept open, as may be required by the sinkers.

Fig. 6. shows the method of fixing a standing set of pumps.

a, The bunton, made of the root end of a large oak, ten feet long and three feet square; hut the larger the better. The inner end, which is the thickest, is placed in a recess cut in the stone, and the outer end is supported by an abutment of solid stone b, left in the pit.

The inner end of the bunton is firmly held down by wooden props cc. f The cistern in which the pumps are placed, and into which the water from another set, either of sinking or standing pumps, may be delivered. The cistern is firmly fixed upon the bunton, and a recess is made in the side of the pit to receive it, and props d may be placed to fasten it down. The larger the cistern the better; there is no rule for regulating its size; but it ought, if possible, to be large enough to contain as much water as will supply its own pump, until the pump below delivers into it when the engine begins to work.

g, The set of standing pumps placed in the cistern. hhnh, The buntons, with their cross collarings, ml.

The buntons have one end fixed in the shaft wa l, and the other is fastened to a cleat k, which is nailed to the shaft brattice ll.

Fig. 7 shows a plan of the manner of fixing a bunton and cistern for supporting a stand-set of pumps.
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aaaa Shows the recess cut in the side of the pit, with the bunton laid in its place. The inner end of the recess is cut dove-tailed, and the bunton wedged into it. so that it is prevented from moving forward by the shock of the pumps when the engine is at work. The dotted lines show the situation of the cistern when placed on the bunton. . .

b, The pumps in the cistern.

cc, The situation in which the succeeding sets of pumps may be placed.

d, The main or shaft brattice.

e, The bunton to which the cross collarings∕∕are nailed, for securing the pumps in their proper position.

As all the operations of the engineers should be performed in the engine-shaft, without interrupting the drawing of coals in the other shafts of a double pit, as much room as possible should be preserved in the engine-shaft, by occupying as small a space in collaring the pumps as circumstances will permit.

For this purpose, iron stirrups have for some time been introduced in the place of cross collarings of wood, with great advantage. .

If the cross collaring, g, fig. 7, was extended to the brattice, as shown by the dotted lines, and fixed to it by a cleat, in the same manner as the bunton e ; by putting an iron stirrup round the pump, with its ends passed through the collaring g, and fastened behind by the screwnuts n, the bunton e and cross collarings ff may be dispensed with, which will give much more room in the engine-shaft.

.. Thus far we have described the most improved methods of winning a colliery of considerable extent and depth. There are two distinct methods of working the coal, the narrow, and the long or broad way. The narrow way is commenced by cutting passages through the coal, both lengthwise and across, leaving rectangular pillars between the passages. By the first operation one third of the coal is generally taken out; but where the strength of the coals and the firmness of the roof will permit, a greater or less proportion of the pillars which remain are afterwards removed, commencing with the most distant, and ending with those nearest the pit. By the broad way, the coal is wrought out at once, frequently for a length of 150 yards in one face, without leaving any pillars of coal to support the r'oof. The former method is adapted to beds of coal which occur at a considerable depth beneath the surface, from 50 to 150 fathoms; the latter to beds which lie nearer the surface, especially if they have a tolerably strong roof.

An improved system having, within the last twentyyears, been brought to a state of high perfection, by the ingenious Mr Buddle of Wall’s End, we are happy in being enabled to avail ourselves of the description of it, as given, under his correction, by Mr Griffith, in his excellent Report on the Leinster Coal District. By means of Mr Buddle’s plan, from seven eighths to nine tenths of the coal is at present raised; whilst, previous to the adoption of his system, but one half, and frequently less, was all that could be obtained; and, therefore, through his exertions, the coal owners of the north of England may be said to have increased their property at least one third, as more coal than is equal to that proportion is now raised out of the same area than could be effected according to the old system.

Mr Buddle’ ’s ingenuity has not been confined to the improvement of the method of working coal; he has also introduced a more perfect system of ventilation, and has put in practice many simple but excellent contrivances, not only to prevent the accumulation of inflammable air in any part, but also by using hanging doors, which yield to the blast of inflammable air, and are not carried away, to prevent a general explosion throughout the mine when any cavity containing inflammable air is broken into accidentally as the works extend. By this means, when the first blast is over, the lives of the colliers and horses in the distant parts are preserved. We shall at present confine ourselves to the different methods of working and supplying fresh air to the most distant parts of an extensive colliery, by one or more pits.

Plate CLXXV. fig. 1, represents the plan of the improved system of working and ventilating collieries in Newcastle-upon-Tyne. A represents the pit; B, the furnace; C, under level drift; D, the staple or air-pit; E, water level line; F, district commencing first working; G, district beginning to take off the pillars; H, district finished the first working; L, double doors.

The circle below the letter A is intended to represent a pit or shaft, divided from top to bottom by a boarded partition nicely joined, so as to prevent the communication of air from one side of the pit to the other. Through the right-hand division of this pit, which is called the downcast, the air descends. Having passed through all the excavations that have been made through the mine, which are represented by the white or uncoloured divisions, it passes up the left-hand division of the pit. To aid the draught of air, a great fire is made in the furnace at B, which rarefies the air, and causes it to ascend more quickly through the upeast pit or division. The arrows point out the direction of the course of the air throughout the mine, and the red marks are walls or stoppings built to force the passage of the air in particular directions. The dark-coloured parts in the plate represent the unwrought part of the coal.

The principal advantage of the new mode of working is, that it divides the mine into any convenient number of districts, each of which is to be wrought out in its turn, and the roof suffered to close in. But to prevent the crush created by the falling in of the roof in one part, from communicating with and injuring the coal in another, a great protecting pillar or wall of coal is left between each division. By examining the figure, the several divisions or districts may be easily traced, by observing the line of large pillars.

The first operation of working the coal is represented clearly in the district E. From the bottom of the pit two parallel passages are cut, three yards broad and twelve yards asunder, at convenient distances; cross-cut passages, or headings, are driven to connect the parallel passages, and thereby create a complete circulation or current of air.

The parallel passages are then continued until air again becomes deficient; a second heading is then cut, and the first is carefully closed up, so as to force the air round a lengthened circuit. This process is continued uninterruptedly round the district, as represented in fig. 1. The district being thus surrounded, broad passages, called boards or rooms, are then commenced at the lower end of the district, and are cut at regular distances upward, towards the parallel passages first described. The breadth of the boards, and that of the pillars of coal left between them, is continually varied, according to the nature of the strata which form the roof and floor of the mine. In the district F, the boards are represented in progress; this is also the case in the district K; when the boards and headings have been made throughout a whole district, this is represented by those of G and H. The next operation is to remove all the pillars; those at the farthest extremity of the district are first cut out. This operation is performed either by commencing at one end, and proceeding regularly to the other, or by cutting the pillar in the middle, '
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and setting a number of men to work at it. But this must depend on the strength of the roof. A few of the pillars of the district BG are represented as being removed, and the whole of the coal that could be carried away is represented as being wrought out of district I, nothing except the trifling quantity represented by the black lines being left behind. When the pillars of the district G have been wrought out nearly to the boundary pillar between the districts I and G, the boundaries should be - divided by boards and headways, and a considerable portion of them may thus be removed.

Owing to the frequent mistakes of sinking pits,in improper situations, the pit A is placed in a position with respect to the colliery, that is frequently seen in practice, namely, a great part of the coal field lying to the dip, or under the natural water level of the pit. By observing the direction of the dip and rise, as represented on the plan by the great arrow, it is evident that, without some contrivance, no coal could be level or water-free below a line drawn across the pit A, at right angles to the arrow; and consequently, half the coal of the districts F and G, and the whole of the district K, must have been left behind. To overcome this evil, the pit A is supposed to be sunk below the coal to a depth more than equal to the level of the coal at M; and a drift or passage is supposed to be horizontally cut through the strata beneath the bed of coal, till it meets the coal at Μ. By this means the district K may be freed from water. Had the pit been originally sunk nearer to M, all the expense and trouble of driving the stone drift would have been avoided.^[3. There are, however, many reasons which may render it expedient, in particular cases, to avoid fixing the engine-pit on the lowest level of the coal-field; as when a slip or dike divides a small portion of the lower part of the field from the rest, &c. In this case the coal wrought to the dip of the pit may easily be brought up to the drawing-pit by a high pressure engine, fixed in some convenient station at the head of an inclined plane. ]

It frequently happens, that the stoppages or walls built to direct the ventilation interrupt the communication from the various parts where the coal is working to the pit bottom. When this happens, a door is placed at a convenient distance on either side of the wall, which may then be removed; and the leader of the coal waggons, as he passes along, opens the first door, and having led his waggons past, shuts it, and then opens the second door, by which means the regular ventilation of the mine is constantly preserved.

According to the plan just described, very extensive collieries are worked from one pit; and passages or boards, amounting in the aggregate to thirty miles in length, are perfectly ventilated by a single pit.

The mode of passing the air through the different passages or boards varies according to circumstances. When a very quick current is required, the air is passed up one board and down the next, or as represented in the plate, or up two boards and down two, or up three boards and down three. But in small collieries, or where no inflammable air is met with, the passages of air round the boundaries of a district, as that of F, leaving all the ends of the passages or boards open for the air to circulate, is found sufficient. At the great collieries at Newcastle, the ventilation consists of a current of air of thirty-six square feet, moving with a velocity of three feet in a second.

The different modes of removing the pillars according to circumstances, are represented in fig. 2, Plate CLXXV. aa, cc, d, and e, are the different modes of working pillars, where it is necessary to preserve the air-courses. The pillars are wrought in the manner represented at bb, where the outer parts are much damaged and cracked by the pressure of the roof and door; and ∕∕ ’ when the roof is not sufficiently strong to remain up while the whole pilar is removing. In this case the centre part is left, and t>oth ends are carried away.

The consequence of working the boards too wide is represented in the elevation, fig. 3. The pillars on either side of the board g, arc represented as much broken both at top and bottom by the pressure of the roof and floor, and the coal is rendered useless. Besides, the passage through the board is nearly closed by the approach of the roof and floor towards each other. The board h represents the appearance in elevation of one that is driven of a proper width. In this case the coal on both sides is solid, and the roof and floor remain in their original positions. In working all collieries, it is better to drive the boards too narrow than too broad. In the first case, when the pillars are to be removed, the roof and the coal are both sound, and the whole of it may with safety be removed; but, in the latter, the centre of the pillars only, as represented by bb in the plate, can be removed.

We shall now lay before our readers Mr Griffith’s account of the broad method of working. A good account may also be found in Mr Farcy’s Survey of Derbyshire.

Many of the shallow and thin beds of coal in Yorkshire are worked in the broad way; but the breadth of the banks vary in almost every colliery, from certain local circumstances. We shall describe one, the principles of which may be applied to any shallow colliery; and the proper breadth of the banks, which depends on the nature of the roof, will be determined better by practice than precept.

Fig. 4 represents a very simple and excellent method of working in the broad way. A shaft is divided into two parts, in the manner already described; BBB are double drifts, with proper headings for air; CC and DD are banks, each thirty yards broad; the dotted marks represent three rows of wooden pillars which support the roof. The light shade represents the parts already worked out where the roof has fallen.

The first operation in the work is to drive the several double drifts. Those on each side of the pit must be completed to the full extent before any other workings can go on. The three double drifts at right angles to the first may then be commenced; and, having advanced twenty or thirty yards, the great working or bank may be commenced by breaking down the coal along the lines EE upwards. The coals are drawn from the face of the banks on both sides, through the openings or headings by which the air is introduced, as represented by the arrows. I and F are double doors to prevent the air from the left bank returning directly to the pit; by this means it is forced along the face of the workings in the right bank. The first banks being proceeded on to a certain distance, a third and fourth may be commenced to the right and left, and others may be wrought to the rise by connecting the rise drifts by cross ones at right angles to them, and working upwards from the cross drifts in the manner that has been described.

According to this plan, a very extensive colliery may be worked from one pit; but horses should be used to draw the coal under ground; and if the coal be thin, part of either the floor or roof must be removed to give sufficient headway. The most approved method of conveying the coals from the face of the work to the pit bottom is the following: First, a light cast-iron railway must be laid from the pit bottom through all the main passages of the colliery, and, branching from these, small movable [7:7:85]railways should be laid, from the nearest point of the main passage, or mother-gate as it is usually called, to the face of the workings. When the collier has broken down the coals, another man, known by the name of putter, hurrier, &c. is employed to fill the coal into a wicker basket or wooden box, placed on a wooden carriage with iron wheels; this is pushed to the mother-gate, along the railway, and the putter returns with an empty box, which has been placed in the mother-gate; a waggon-boy arrives from the pit, leading a horse, which draws six carriages chained together, each having an empty box on it. These boxes are lifted off; and, by means of a small crane, the full boxes are successively raised and placed on the carriages, which, when thus laden, are drawn by the horse along the railway to the pit bottom, whence the boxes are drawn up to the surface, and the empty ones returned.

The reader will find much useful information on the ventilation of mines in Mr Buddle’s valuable tract, entitled The First Report of the Sunderland Society for preventing Accideìits in Coal Mines.