QUARRYING is the operation of extracting from the ground, or detaching from the sides of rocks, marble, stone, or other minerals in considerable masses. When the material to be excavated lies vertically below the surface of the ground, the work commences by remov ing the earth to a depth sufficient to lay that material bare, in order that it may be separa ted into blocks, and removed ; but when the stone, &c., is in the interior, and near the side of a mountain or hill, the workmen proceed as in the operation of mining, running galle ries into the ground, and leaving pillars of the material for the support of the mass above 'them.
A quarry of small extent is opened by sink ing vertically in the ground a shaft, into which the men descend by ladders; and the blocks of stone, being separated from the mass, are drawn up by means of cranes, which are worked by a windlass or other machine. In working the larger quarries, the vegetable mould form ing the upper surface is removed by the spade ; and the beds immediately underneath, gene rally consisting of rag, or stone of an inferior quality, are broken up by gunpowder or other wise, and conveyed to a distance. The stones intended for sale, and which are generally in beds much below the surface, are sometimes also detached from the mass by blasting; but as by this process the blocks are broken irre gularly and the stone wasted, a different me thod is generally employed. The large mass of stone, as it exists in the quarry, consists of strata contiguous to one another, and the surfaces in contact form planes of cleavage ; in lines parallel to which the stones being more easily divided than in any other direc tion, these lines constitute what is called the cleaving grain of the material. In order there fore to separate a large block from the mass, a series of iron wedges, placed in line a few inches asunder, on the natural face of the rock and in the direction of the cleaving grain, are driven into the stone till a part is loosened : a channel is then cut in the direction of the length of the intended block, and at a distance from the natural edge of the stone equal to its required breadth; and wedges being planted in the channel, they are driven by repeated strokes till the stone is split in that direction also. In the hardest stones, the wedges are
placed not in the channels, but in what are called pool holes sunk in the direction in which the block is to be severed from the mass, A similar operation is then performed in the direction of the breadth of the block ; and thus a large portion is detached from the ori ginal mass.
The natural strata of the stone in different quarries are in different positions ; frequently they are horizontal, but generally they are inclined to that plane, and sometimes they are vertical : occasionally also both the first and last of these positions are assumed by the stone in the same quarry. It is evident that the separation of the blocks from a mass must be most easily effected when the natural strata are in vertical positions ; cutting the stone in directions perpendicular to the line of the grain is always a work of difficulty, and the operations are attended with some danger to the quarry-men when the latter are obliged to work in galleries under ground.
After the blocks have been severed from the mass, they are reduced as nearly as pos sible to a rectangular form ; and this is done by means of a tool called a kevel, pointed at one end and flat at the other, with which the irregular parts are knocked off. The blocks are then usually, by means of cranes which are capable of being moved from place to place, raised upon trucks or low carriages ; and these are drawn, generally on iron rail ways, to the quays or wharfs where the stone is put on ship-board. At the slate quarries in Caernarvonshire the slabs are placed on sledges, which,-by an engine, are drawn up an inclined plane ; and, from the summit of this plane, the stone is drawn by horses to the Menai.