STONE WORKING. There are three aspects under which the working in stone presents itself to our notice—quarrying, shap ing and preparing the stones, and masonry properly so called.
All statuary marble and all building stone are extracted from the rocks by quarrying. Egypt, Greece, and Italy possessed the quar ries from which the great works of the ancients in sculpture and architecture were produced; and nearly every country possesses quarries more or less extensive. The British isles abound with stone of nearly every different kind that can be employed with advantage in architecture and engineering. The granites of Aberdeenshire, of Devon and Cornwall, and of Ireland ; the sandstones of Yorkshire, Lan cashire, Derbyshire, and other counties ; the millstone grit of Yorkshire ; the slate-stones of Wales, Cumberland, Cornwall, and Ireland ; the limestones of Portland, Purbeck, Bath, and other counties ; the claystones of Gloucester shire and Yorkshire ; the capstone of Kent— all are plentiful.
In quarrying stone the works are chiefly horizontal or vertical, according as the stone is far below or near the surface. Stone of inferior kind has generally to be removed before the good stone can be reached. The huge masses are often loosened by blasting with gunpowder ; but as this shatters the blocks, a slower but less wasteful plan is usually adopted. Most stones present natural layers or places of cleavage, which enable it to separate into parallel strata; and the quarry men employ their nicks and jumper-chisels in such a way as to take advantage of this cleavage. After the blocks have been severed from the mass, they are reduced as nearly as possible to a rectangular form ; 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 raised upon low carriages, and drawn on iron railways to the quays or wharfs where the stone is put on shipboard.
The working of stone is similar in principle to that of marble, but does not necessitate so much care. In the common mode of sawing
a stone, a man works to and fro a framed saw or cutter, which gradually cuts its way through the stone ; the instrument is not really a saw, for it has no teeth ; but by the use of sand and water an abrading action is produced which wears a cut in the stone. In the large marble and stone works, of which a fine example has been established at Pimlico, several stone saws are framed together in parallel array, and worked by a steam-engine ; a block of marble or stone is thus quickly cut up into slabs. Slabs are cut up into smaller pieces by hand saws, or more expeditiously by circular saws fixed upon a revolving axis—the saws, as in the former case, being in fact blunt knives. By bending these blunt knives into a circular or cylindrical form, and fixing them at the bottom of a vertical revolving shaft, circular pieces of stone aro cut. Pillars and hollow cylinders or pipes of stone are shaped by similar means. If, instead of a saw, the hori zontal axis be furnished with iron wheels shaped with mouldings on their edges, the forms of architectural mouldings may ho wrought on long slabs of stone.
The smoothing and polishing of stone and marble are effected by the friction either of a smooth iron surface, or of another piece of stone, plentifully wetted during the process.
Masonry is a most important branch of art, as connected both with architecture and with common building, but especially the former. Owing to its expense, masonry is comparatively rarely employed in England, except for public or other buildings of the highest class : the mason's work being in other cases re stricted to such parts as door-steps, string courses, facies, plain cornices, pavements, and stairs. Walls which are not of solid masonry throughout, but are built either of brick or inferior stone and rubble,with only an external facing of squared stone laid in courses, arc termed ashler or ashlering.