in the other places, they may be very different both in their order and thicknesses, and yet of the same kinds. Though they be thus found very different in one coalery, or district, from what they are found to be in another, with respect to their thicknesses, and the order in which they lie upon each other, yet we never meet with a stratum of any kind of matter but what belongs to some of those above described. To illustrate how the various strata lie in some places, and how often the same stratum may oc The cur betwixt the surface and the coal, we shal give the following example. The numbers in the left-hand column refer to the classes of strata before described, to which each belongs. second column contains the names of the strata ; and the four numerical columns to the right hand, express the thickness of each stratum in fathoms, yards, feet, and inches. In the following instance the species of sand-stone only occurs twice, and that of post five times, whilst the shiver occurs no less than nine times. To apply the foregoing observations to practice: suppose it be required to examine whether there be coal in a piece of ground adjoining to, or in the neighbourhood of, other coaleries. It is proper to be informed, at some of the adjacent coaleries, 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; if any dikes, ditches, or troubles, and the course they stretch Having learned these circumstances, search in the ground under examination, where the strata are exposed to examination, and compare these with the other. If they be of the same kinds, and nearly correspond in order and thickness, and by lying in a regular manner, and agree by computation with the dip and rise, it may be safely concluded that coal is there; and the depth of it may be judged from the depth of the coal in the other coalery, below any particular stratum which is visible in this. II. 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 kinds of strata are found there as in the adjacent coalery, and there is reason from the dip and other circumstances, to believe that the stretch through the ground to be exa 25 mined, it may be concluded that the coal is there, as well as these other strata. Suppose a coalery 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 towards 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 in the place F; where, if they be found in the manner before mentioned, and there be reason to believe they extend regularly from the first place to this, it is more than probable the coal, as well as these strata, will be found in the intermediate ground. III. If the ground to be examined lie more to the rise of the coal, as at E, which being supposed to be on a flat, perhaps the solid strata there may be wholly covered by the gravel, clay, &c. of the outward surface lying upon them: in this case, by measuring the horizontal distance and the descent of ground from A to F and computing the quantity of ascent or rise of the coal in that distance by comparing these together, it may be judged at what depth the coal will be found there, allowing that it lie regular. 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 yards of horizontal distance : Yds. 80 24 56 50 6 IV. Suppose that the place at B is 500 yards the contrary way, or to the full dip of the coal at A; if a view of the solid strata canno be obtained, then, by proceeding in the same manner as before, the depth of the coal at that place may be computed. Thus, Yds. 80 130 V. The proper step to be taken in such a case, is to take a general view of that district of country intended to be searched, in order to judge from the outward appearance or face of the country, which particular part, out of the whole, is the most likely to contain those kinds of strata favorable to the production of coal; and consequently the particular part thus found, is the most advisable to be begun with, in the examination. Though the appearance of the outer surface give no infallible rule to judge of the kinds of strata lying beneath, yet it gives a probable one; for it is generally found, that a chain of mountains or hills rising to a great height, and very steep on the sides, are commonly composed of strata much harder and of different kinds from those before described wherein coal is found to lie, and therefore unfavorable 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 favorable 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 the mountainous situations are found more favorable 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, 50 sometimes of considerable extent, do more commonly contain coal, and those kinds of strata favorable to its production, than either the mountainous or champaign countries; and a country so situated as this last described, especially if at some considerable distance from the mountains, ought to be the first part appointed for particular examination. Plains and level grounds of great extent, generally situated by the sides of rivers, or betwixt such moderately rising grounds as last described, are also very favorable 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 favorable in the rising grounds, on both sides of the plain, and not so in the space betwixt them. Though plains be so favorable, in such circumstances, 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 being fixed upon which abounds with moderate hills and valleys as most suitable for the proposed examination, 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 80 50 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 upcast dike of ten fathoms or twenty yards towards B, then deduct twenty from fifty, the depth before computed, 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 such a distance from all other coaleries, that by reason of the intervention of hills, valleys, unknown dikes, &c., the connexion or relation of the strata with those of any other coalery cannot be traced by the methods last mentioned; in which case a more extensive view must be taken of all circumstances than was necessary in the former; and a few general rules founded on the foregoing observations, and on conclusions drawn from them, will greatly assist in determining sometimes with a great degree of probability, and sometimes with absolute certainty, whether coal be in any particular district of country or not. upon each other, the point of the horizon to which they dip or incline, and the quantity of that inclination, and whether they lie in a regular state. 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 connexion with some other in a second place, and if this other has a connexion with another in a third place; &c., then, from these separate connexions, 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 these 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 that 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 sight by the surface of earth or other matter. VI. 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 bear a mud or sediment of the color of rust of 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 streams or rills. The stratum of coal is the most general reservoir of this water; for the iron-stone 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 ochrey matter in the water, when it comes from a stratum of coal, is of a darker rusty color than when it proceeds from any other, and often brings with it particles and small pieces of coal; therefore, wherever these two circumstances concur in a number of these 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, and are not distinguishable from common water, otherwise than by their astringency, and their having a blue scum of an oily or glutinous nature swimming upon the surface of the water. These, in common with the others, bring out particles of coal, more especially in the rainy seasons, when the springs flow with rapidity. When a number of these kinds are situated from each other in the direction of the strata, as above described; or if the water does not run forth as in springs, but only forms a swamp, or an extension of stagnant water be neath the turf; in either case, it may be depended upon that this water proceeds from a stratum of coal. VII. 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 appear ance of the other strata be very favorable, and afford a strong probability of coal being there; and if the last mentioned method of judging of the particular place where the crop of the coal may lie, by the springs of water issuing from it, should, from the deficiency of those springs or other circumstances, be thought equivocal, and not give a satisfactory indication of the coal; then a further search may be made in all places where the outward surface, or the stratum of clay or earth, is turned up by ploughing, ditching, or digging, particularly in the lower grounds, in hollows, and by the sides of streams. These places should be strictly examined, to see if any pieces of coal be intermixed with the substance of the superior lax strata; if any such be found, and if they be pretty numerous and in detached pieces, of a firm substance, the angles perfect or not much worn, and the texture of the coal distinguishable, it may be concluded, that the stratum of coal to which they originally did belong is at no great distance, but in a situation higher with respect to the horizon; and if there be also found along with the pieces of coal other mineral matter, such as pieces of shiver or freestone, this is a concurrent proof, that it has come only from a small distance. Though the two fore-mentioned methods should only have produced a strong probability, yet if this last mentioned place, where the pieces of coal, &c. are found in the clay, be in a situation lower than the springs; when this circumstance is joined to the other two, it amounts to little less than a moral certainty of the stratum of coal being a very little above the level of the springs. But if, on the contrary, these pieces of coal are found more sparingly interspersed in the superior stratum, and if the angles are much fretted or worn off, and very little of other kinds of mineral matter connected with them; it may then be concluded that they have come from a stratum of coal situated at a greater distance than in the former case; and by a strict search, and an accurate comparison of other circumstances, that particular place may be discovered with as much certainty as the other. After the place is discovered, where the stratum of coal is expected to lie concealed, the next proper step to be taken, is to begin digging a pit or hole there perpendicularly down to find the coal. If the coal has no solid strata above and beneath it, but be found only embodied in the clay or other lax matter, it will not be there of its full thickness, nor so hard and pure as in its perfect state when enclosed betwixt two solid strata, the uppermost called the roof, and the undermost the pavement, of the coal: in such situation therefore it becomes necessary, either to dig a new pit, or to work a mine forward until the stratum of coal be found included 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 favorable circumstances attending each of the modes of enquiry; and the result accordingly admits every degree of probability, from the most distant, even up to absolute certainty. In some situations, the coal will be discovered by one method alone; in others, by a comparison of certain circumstances attending each method; whilst, in some others, all the circumstances that can be collected only lead to a certain degree of probability. In the last case, where the evidence is only probable, it will be more advisable to proceed in the search by boring a hole through the solid strata, than by digging or sinking a pit, it being both cheaper and more expeditious; and in every case which does not amount to an absolute certainty, this operation is necessary, to ascertain the real existence of the coal in that place. We shall now suppose, that having examined a certain district, situated within a few miles of the sea or some navigable river, that all the circumstances which offer only amount to a probability of the coal being there, and that boring is necessary to ascertain it; we shall therefore describe the operation of boring to the coal. Suppose that the ground A, B, C, D, fig. 4, has been examined, and 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, &c. the strata cannot be viewed in the low grounds; therefore, in this, and all similar situations, the first hole that is bored for a trial for coal should be on the west side of the ground, or to the full rise of the strata as at A, where, boring down through the strata 1, 2, 3, suppose ten fathoms, and not finding coal, it will be better to bore a new hole than to proceed to a great depth in that: therefore, proceeding so far to the eastward as B, where the stratum 1, of the first hole, is computed to be 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 so far to the eastward, as it may be computed the stratum 4 of the second hole will be met with at the depth of ten or twelve fathoms, a new hole may be bored at C; where, boring through the strata 9, 10, 11, 12, the coal is met with at 13, before the hole proceed so deep as the stratum 4, of the former. It is evident, that, by this method of procedure, neither the coal nor any other of the strata can be passed over, as the last hole is bored 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 coaleries. In coaleries of great extent, although the coal be known to extend through the whole grounds, yet accidental turns, and other alterations in the dip, to which the coal is liable, render the boring of three or more holes necessary, to determine exactly to what point of the horizon it dips or inclines, before any capital operation for the winning of it can be undertaken; because a very small error in this may occasion the loss of a great part of the coal, or at least incur a double expense in recovering it. Suppose A, B, C, D, fig. 5, to be part of an extensive field of coal intended to be won or laid dry by a fire engine; according to the course of the dip in adjoining coaleries, the point C is the place at which the engine should be erected, because the coal dips in direction of the line AC, consequently the level line would be in the direction CD; but this ought not to be trusted to. Admit two holes, 1, 2, be bored to the coal in the direction of the supposed dip, at 200 yards distance from each other, and a third hole, 3, at 200 yards distance from each of them: suppose the coal is found, at the hole 1, to be twenty fathoms deep; 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, is to 200 yards the distance, so is eight fathoms, the dip from 1 to 3, to 160 yards, the difference from one, on the line 1 2, to a, the point upon a level with the hole 3. Again say, As eight fathoms the dip from 1 to 3, is to 200 yards the distance, so is ten fathoms, the dip from 1 to 2, to 250 yards, the distance from 1, in direction of the line 1, 3, to b, the point upon a level with the hole 2. Then let fall the perpendicular 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 ch, by which means about onethird part of the field of coal would have been below the level of the engine, and perhaps lost, without another engine was erected at D. Boring not only shows the depth at which the coal lies, but its exact thickness; its hardness; its quality, whether close burning or open burning, and whether any foul mixture is in it or not; also the thickness, hardness, and other circuinstances, 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 poses, they may be fixed (as near as can be guessed) in such a situation from each other, as to suit the places where pits are afterwards to be sunk; by which means most of the expense may be saved, as these pits would otherwise require to be bored, when sinking, to discharge their water into the mine below. There are many other uses to which boring is applied. It is generally practised in England, and is brought pur to great perfection; and as the operation is generally entrusted to a man of integrity, who makes it his profession, the accounts given by him of the thickness and other circumstances of the strata, are the most accurate imaginable, and are trusted to with the greatest confidence; for as very few gentlemen choose to take a lease of a new coalery which has not been sufficiently explored by boring, it is necessary the accounts should be faithful, being the only guide to rule the landlord in letting his coal, and the tenant in taking it. The 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 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 let ting 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 pulverised matter, which was worn off the stratum in the last operation, is brought up. By this substance, the borers know exactly the nature of the stratum they are boring in; and by any alteration in the working of the rods (which they are sensible of by handling them) they perceive the least variation of the strata. The principal part of the art depends upon keeping the hole clean, and observing every variation of the strata with care and attention. Having, by one or other of the methods above described, ascertained the existence of the coal mine, the next object of consideration is the method of working it. The most remarkable coal work that we have ever had in this island, was that wrought at Borrowstownness, under the sea. The veins of coal were found to continue under the bed of the sea in this place, and the colliers had the courage to work the vein nearly half way over: there being a mote half a mile from the shore, where there was an entry that went down into the coal-pit, under the sea. This was made into a kind of round key or mote as they call it, built so as to keep out the sea, which flowed there twelve feet. Here the coals were laid, and a ship of that draught of water could lay her side to the mote, and take in the coal. This famcus coalery belonged to the earl of Kincardine's family. The fresh water, which sprung from the bottom and sides of the coal-pit, was always drawn out upon the shore by an engine moved by water, that drew it forty fathoms. The coal-pit continued to be wrought many years to the great profit of the owners, and the wonder of all that saw it; but, at last, an unexpected high tide drowned the whole at once; the laborers not having time to escape perished in it. 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 labor of men to draw off or conduct them away; for it most commonly happens that the stratum of coal, and the other strata adjacent, abound so much in feeders of water, that, before access can be had to the coal, some other methods must be pursued to drain or conduct away these feeders: therefore, after the deepest part of the coal is discovered, the next consideration is of the best method of draining it, or, in the miner's language, of winning the coal. If the coal lie in such an elevated situation, that a part of it can be drained by a level brought up from the lower grounds, then that will be the most natural method; but whether it be the most proper or not, depends upon certain circumstances. If the situation of the ground be such that the level would be of a great length, or have to come through very hard strata, and the quantity of coal it would drain, or the profits expected to be produced by that coal, should be inadequate to the expense of carrying it up; in such case some other method of winning might be more proper. Or suppose, in another case, it be found, that a level can be had to a coalery, which will cost £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 fire engine, or some other machine, can be erected on that coalery 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 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 is 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 a reasonable time, and at an adequate expense, to drain a sufficient tract of coal, it is then the most eligible method of winning; because the charge of upholding it is generally less than that of upholding fire-engines or other machines. If a level is judged most proper, after every consideration of every necessary circumstance, it may be begun at the place appointed in the manner of an open ditch, about three feet wide, and carried forward until it be about six or seven feet deep from the surface, taking care to secure the bottom and sides by timber-work or building; after which it may be continued in the manner of a mine about three feet wide, and three feet and a half high, through the solid strata, taking care all along to keep the bottom upon a level, and to secure the roof, sides, and bottom, by timber or building, in all places where the strata are not strong enough to support the incumbent weight, or where they are liable to decay by their exposure to the fresh air. If the mine have to go a long way before it reach the coal, it may be necessary to sink a small pit, for the convenience of taking out the stones and rubbish produced in working the mine, as well as to supply fresh air to the workmen; and if the air should afterwards turn damp, then square wooden pipes made of deals closely join |