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. [Illustration: 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. [Illustration: SECTION OF A LEAD MINE IN CARDIGANSHIRE. _a._ Shafts. _b._ Levels. ]