some hard, some soft, some tough, some tender-but such are the alternating beds of the coal-formation, whether one thousand or ten thousand feet in thickness. None of these rocks are difficult of excavation; but some of the softer sandstones are falsebedded or obliquely laminated, and apt to slip in, and many of the shales are short and tender (breezy, shivery, or brashy), and must be walled or planked to insure stability. Even in blasting through solid sandstone, care should be taken not to break or shake them unnecessarily, by placing the charge too near to the sides; and it will be found better in the long-run to pay a little more for extra hewing than to endanger the safety of the shaft by broken and tender walls. Occasionally in our coalfields, and especially in those of Scotland, interstratified masses of basalt or whinstone are met with, and these, though making strong and durable walls when sunk through, are often troublesome and expensive, generally costing more per foot than the ordinary stratified rocks cost per fathom. When such masses are unexpectedly met with in sinking, the engineer should make every effort to discover whether they are interstratified or intrusive, or whether they may not be old necks of eruption -because, in the latter case, all further effort would be hopelessly useless.

When the Carboniferous strata are overlaid by any of the newer formations, as the Magnesian limestone in Durham, the Trias and Oolite in the midland counties, or the Chalk and Tertiary in Belgium, these softer and more varied beds require greater care, and entail a heavier outlay. Some of the Magnesian limestone beds in the neighbourhood of Sunderland are absolutely waterlogged, and require most expensive tubbing. The "waterstones" of the Trias are also troublesome, while some of the marls have little or no coherence. Indeed there are few sinkings in which tender or water-bearing beds do not occur, requiring either buildings of brick or stone, plankings of wood, or tubbings of cast-iron.

Winning the Stratum or Seam.

In winning any stratum, whether coal, shale, fire-clay, ironstone, limestone, or rock-salt, a great deal depends upon its hardness or softness, the nature of the roof and floor, the presence of water, and the occurrence of dangerous gases. Hard coals, like splint and cannel, require a different treatment from soft and tender ones; tough shales and fire-clays cannot be dealt with like jointed crystalline limestones; and a roof of short shivery shale cannot be trusted like one of a solid, stony nature. Wet winnings require different arrange

ments from dry ones; and "fiery seams," precautions that are altogether unneeded in the working of those that are free from explosive gases. Of course, some of these contingencies cannot be known till some progress has been made with the winning; but the moment they make their appearance, plans should be adopted to meet them-and these plans of a substantial and permanent kind, as being always safer and cheaper in the long-run than any tinkering and temporary expedients. Once a roof has shown symptoms of tenderness by occasional falls, or a seam of coal fieriness by occasional blowers, there should be no relaxation of carefulness on the part of the miner or mining engineer. There may have been no accident for months; but the very next stroke of the pick may bring about the catastrophe for which this temporary security, by lulling their watchfulness, has left them wholly unprepared. Much of this is, no doubt, technological, and belongs to the art of mining rather than to geology; but a knowledge of the structure and texture of the rocks with which he has to deal is ever of paramount importance to the mining engineer.

The same may be said of the modes of underground working the laying out of main-ways, water-levels, air-courses or circuits of ventilation. And these, again, depend on the nature of the seams, whether they can be worked by the panel

method-post-and-stall, bord-and-pillar, stoop-and-room, of the miner-or by the long-work or long-wall method. In the former method the seam is hewn out in many drifts, galleries, or bords, separated from each other by wide ribs of coal. These

again are crossed at right angles by similar bords, so as to leave square pillars of support, which vary in size according to the tenderness of the roof and coal, or the softness of the floor. When these galleries have reached the boundaries of the field, or as far as it is expedient to carry them, the next step is to remove the pillars, or as much of them as can be safely accomplished, by working back to the shaft and allowing the roof to subside the excavated and deserted portion, now filled with debris constituting the waste, goaf or gob of the miner (G). In the latter method, the main-ways are carried out to the boundary, and then the whole of the coal is removed by working the face backwards to the shaft, care being taken to maintain a free and accessible face by packing or propping, and then ultimately to allow the roof to subside. In some cases, the working face is carried back from the shaft, and the ways maintained by build

ing, packing, and planking; but generally speaking, the former plan is preferred. In some coal-fields a combination of longwall and bord-and-pillar is adopted-much depending, of course, upon the nature of the seam, roof, and floor. Again, where the seam lies at a high inclination, the main-ways are carried obliquely to the rise, in order to reduce the difficulty of ascent and descent-a matter of main importance when the angle of inclination exceeds 10 or 12 degrees.

Speaking of the comparative merits of the two methods, Mr Warrington Smyth, in his "Treatise on Coal and Coal-Mining,' appropriately observes: "The great advantages of the long

work method are, simplicity of plan (and consequently of ventilation), and the entire removal of all the coal,—added to which, under most circumstances, are greater safety to the men, and a larger proportion of round coal in comparison to small or slack-a matter which, considering the prices, is of vital importance in the selection of the mode of working. It has been mostly practised where the seams are thin, or where they contain a band of refuse; but neither condition is indispensable for, on the one hand, coals of 6, 8, or 9 feet thick are at the present moment worked advantageously in this manner; and on the other, we have seen bind or stone-debris carried from one seam to another, or even taken down from the surface to assist in the packing where it was needful. Nor is it necessary that the roof be good, although the expense will be very different according to its fragility; but if the operations be carried on with sufficient smartness to push the working-place daily under a fresh or "green" roof, it may be managed upon this system, even when composed of mere fire-clay with slippery joints. Only a few years have passed since the long-wall was much decried, except in a few localities; but its manifest economy is gradually introducing it elsewhere; and even in some of the deepest Durham collieries it is successfully applied to the working off of their gigantic pillars; whilst in a few of the pits near Dudley it has been employed for removing bodily first the upper and afterwards the lower half of the 10yard coal, with greatly increased yield of coal and security to life." To these remarks we may add the applicability of coalcutting machines to the long-wall system, as one of its chief recommendations-these machines coming more and more into use alike on the score of economy and of freeing the miner from the most laborious and dangerous part of his duties.

And here it may be further observed, that with the yearly increasing consumption of mineral produce, the gradual increase of prices (coal in particular), and the certainty that the supply is limited, and must sooner or later come to an end, it should be the effort of every mining engineer to raise the largest possible amount from any one seam, or, what is the same thing, to leave the smallest possible portion of it beneath ground. Where the long-wall system can be practised with safety, nothing is left, and nothing more can be desired; but in the bord-and-pillar method, a large portion, even with the most daring and dexterous harrying or removing the pillars, is always left beyond reclaim; and it is certainly worth while to adopt the other method wherever it possibly can, with due regard to the safety of the miner.

But whatever system may be adopted to remove the seambe it coal, fire-clay, shale, or ironstone-care should always be taken to study not only its own structure and texture, but the nature of the roof and floor by which it is bounded, so as at once to insure safety to the workman and prevent undue waste of the material. Some floors are soft, and rise or "creep" under the adjacent pressure, and may thus interfere with the ventilation. Some roofs of shale are slippery, or full of "slicks ;" and others of sandstone are jointed and shivery, and thus require frequent proppings and packings to prevent falls. The whole secret of successful mining lies in raising the largest amount of material in the best condition from any given space, and that at the cheapest rate, and with the greatest safety to the miner. We say the largest amount of material in the best condition; for it must be admitted that in many of our coal-fields the structure of the seams is too little studied, and the result is a large amount of small coal and slack, which might be avoided by the adoption of more skilful methods.

To secure these conditions of economy and safety, the mining engineer should make himself thoroughly acquainted with the structure of his field, noting every fault and dislocation, its amount of throw and direction-every dyke, its direction and effects on the adjacent strata, whether faulting or altering them-every thinning and thickening of strata-the nature of the beds at points where "blowers" of gas occur— and, in fine, every irregularity and unusual appearance that presents itself. These, carefully and distinctly noted on his working plans, will be guides and directions in all his future winnings; and it is simply for want of such plans that so many accidents occur, by breaking into old workings full of gas or water, and so much money is spent in trial-drifts, cautionborings, and the like, where nothing of the kind would have been needed had former experiences been properly plotted and registered as they ought to have been. No doubt things are now in a better condition in this respect than they were thirty or forty years ago; but much yet remains to be done and enforced as a national necessity.

Our coal-fields are limited, and, with an annual output of between 120,000,000 and 130,000,000 tons, are gradually becoming poorer, and seams now neglected, and boundaries between estates now left unworked, must sooner or later be fallen back upon. Under such circumstances, it would be no undue interference with private rights on the part of the Legislature not only to enforce minute plans and records of every working, but to regulate the extent or removal of boundaries, as well as