Limestone is found in Scotland, where it is occasionally employed for architectural purposes. It is also plentiful in many tarts of Ireland ; and quarries of this material, of a rich kind, have been opened in Queen's county, and in the counties of Dublin, Meath, and Cork. The limestone district of Kilkenny is famous for its quarries of black marble so much used for ornamental purposes; and good flagstones for paving are obtained at Shawhill in the same county.
The quanies in the Cotswold Hills in Gloucestershire afford in abundance a iblue claystone for building; and the best stones for pavements are obtained from those at Ealand, or Eland, near lialifax in Yorkshire. The quarries near Maidstone, on the south bank of the Medway, produce much of what is called ragstone, a material which is occasionally used in Kent for building, but chiefly in the construction of sea-walls and for paving the roads. Lastly, about Reigate and Godstono in Surrey is found a soft steno which has the property of withstanding the action of fire, and which on that account is much used for chimneys, ovens, and furnaces; but it is scarcely lit for arty other purpose. " A valuable table of the principal quarries of sandstone and limestone in England accompanies the Report concerning the Qualities of Stone with reference to the New Houses of Parlia ment' (1839).
Having thus explained the nature of quarries, we proceed to notice quarrying, which is the operation of extracting from the ground, or detaching from tho aides of rocks, marble, stone, or other minerals, in considerable masses ; generally also this operation is accompanied by a reduction of the masses to rectangular forms.
When the material to be excavated lies vertically below the surface of the ground, the work commences by removing the earth to a depth sufficient to lay that material bare, in order that it may be separated 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 galleries 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 sinking 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 forming the sipper surface is removed by the spade; and the beds immediately under smith, generally consisting of rag, or stone of an inferior quality, are broken up by gunpowder or otherwise, and conveyed to a distauce.
The stones intended for sale, and which are generally in beds much below the surface, are sometimes also detached from the mass by blast ing (Misre:u]; but as by this process the blocks are broken irregularly and the stone wasted, a different method is generally employed. The large mass of stone, as it exists hi the quarry, consists of strata con tiguous one to 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 direction, these lines constitute what is called the dearing grain of the material. In order, therefore, to sepa rate a largo 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 bo 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 original 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 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.