The Subterranean World

by G. Hartwig

Boring through hard stone is necessarily a very tedious work, but as it proceeds it awakens not only in those who are directly interested in its success, but in every intelligent witness, all the stirring emotions of a game of chance. ‘Of all branches of business,’ says Williams, a thoroughly devoted miner—‘of all the experiments that a man of sensibility can be engaged in, or attend to, there is, perhaps, none so amusing, so engaging, and delightful as a successful trial upon the vestigia, or appearances, of a seam of coal, or other mineral discoveries. When you are attending the people who are digging down or forward upon the vestige of the coal, and the indications are increasing and still growing better under your eye, the spirit of curiosity and attention is awakened, and all the powers of expectation are elevated in pleasing hopes of success. And when your wishes are at length actually fulfilled—when you have discovered a good coal of sufficient thickness, and all circumstances are favourable, the heart then triumphs with solid and satisfactory joy.'

In a mining country like England, where the spirit of enterprise is continually on the look-out for new sources of profit, it may naturally be supposed that searches for coal or metallic ore must be frequently undertaken. Thus in all our mining districts there are professional master-borers, who engage for a fixed price to drill the hardest rock to any depth that may be required.[^[35]] Their chief implements are boring-rods, made of the best and most tenacious Swedish iron; chisels fitted with screws, tipped with good steel, with a face of two and a half to three and a quarter inches, and generally eighteen inches in length; and a wimble, which is a hollow iron instrument like an auger, whose cavity is from six to ten inches in length, with an opening up at one side, with partial overlap, the better to receive and hold the chopped strata.

When the bore is intended to penetrate to a considerable depth, a lofty triangle of wood is set above the bore-hole. In boring, the lowermost rod is the chisel, which continually operates on the rock or stratum. The uppermost rod terminates in a stout ring, through which passes a cross-piece held by two men in working, and which is also suspended to a springing pole by a chain. One or more rods being pushed into the ground, two men on a wooden stage take hold of a cross stave at the end of the springing pole and work it steadily up and down, while two men below, by means of the cross-piece, at the same time heave the suspended rods a few inches, and then allow them to fall by their own weight, walking slowly round the hole. By these combined operations of chopping and scooping the workmen make slow but sure way through whatever substance may be in contact with the chisel. When the hole is too deep, and the added rods become too heavy to be conveniently lifted by manual labour, a brake or lever, or a horse-gin or steam-engine, is employed. As the boring proceeds, it is also frequently necessary to lower pipes into the hole made, to prevent the falling of fragments from the sides of the cylinder.

PROCESS OF BORING.

When the position of a mineral vein is ascertained, its direction known, and some reasonable conjecture made concerning its extent, thickness, and value, measures must be taken to obtain, by subterraneous excavation, the buried mineral, and for this purpose vertical pits or shafts must be sunk, and horizontal galleries, or, as they are sometimes called, levels, must be driven, to prepare the way for its convenient extraction, and at the same time to carry off, so far as may be, the water which either rises into the mine from springs, or drains into it from the surrounding strata. Some idea may be formed of the extent of these works in many of the more considerable mines, when we learn that the total amount of sinking in the Consolidated Mines in Cornwall is stated to amount to more than twelve miles of perpendicular depth (including, of course, the winzes or underground shafts), and that the horizontal galleries extend to as much as forty miles in length. A mine like this is, in fact, a large subterranean town, with numerous lanes and avenues, passages and thoroughfares.

SECTION OF A LEAD MINE IN CARDIGANSHIRE.
a. Shafts. b. Levels.

In sinking a shaft, danger is to be apprehended both from the falling in of loose and incoherent strata, and from the lateral springs, which sometimes empty themselves into the workings to an extent which it would at first appear hopeless to contend against. In such cases there is no safety to be obtained without walling the shaft with brick or stone, or securing it by timber or metal tubbing. For this purpose many of our coal pits were formerly lined throughout with three-inch boards, nailed to a circular wooden framework called a crib, which was firmly attached to the sides of the pit at convenient distances. But this method, although it has been known to keep out a pressure of water equal to 100 pounds on the square inch, is not considered so safe as the metal tubbing now adopted in all difficult works. In comparatively solid ground the cast-iron tubs are forced down the shaft, but in soft ground they sink by their own weight. As they descend, fresh tubs are added, until the work is finished. When we consider that, in the coal-pits in the north of England, many shafts have a diameter of as much as fifteen feet, that in some cases they are sunk to a depth of nearly 300 fathoms, and that, under the most favourable circumstances, even where tubbing is not required to guard against the influx of springs, it is necessary to line almost the whole of the interior with bricks, to prevent the loose strata from falling or being washed in, we cannot wonder that as much as 100,000l. and ten years of labour have, in some cases, been expended before the seam of coal has been reached that was to repay all this vast outlay of capital and time. Unsightly and filthy as such a shaft may be, it is in reality a great triumph of architectural skill.

In most of our collieries one shaft serves for winding up the coal, for the passage of the men up and down, for ventilation, and for drainage by means of the engine-pumps. To answer these various purposes it is subdivided or bratticed by brick or wooden partitions into two, three, or four compartments; but this arrangement is very defective, for the safety of the workmen requires that in every large coal-pit, and indeed in every mine, there should be at least two separate shafts. When the partitions of the single shaft become injured or burnt, which has not unfrequently been the case, the ventilation of the pit may suddenly be deranged, and many lives have thus been endangered. The obstruction of a shaft by the breakage of an engine has caused some of the most appalling tragedies in mining history. On January 10, 1862, the beam of the pumping engine broke at the Hartley Colliery in the Newcastle coalfield, and striking, like a huge catapult, with its enormous weight of forty tons, against the sides of the shaft as it descended, accumulated an enormous mass of rubbish and broken timbers at the depth of 138 yards from the surface. Two hundred and four colliers were thus shut out from all hope of rescue, for no exertion could possibly remove, in time enough to save them, the vast pile of ruins that obstructed their escape to the upper world.