A cavity or opening made by miners in rocky ground, from which are procured marble, freestone, slate, limestone, or other materials; one of which, in the island of Jersey, is represented in the subjoined cut; from whence is obtained large quantities of stone for the London pavements. It is of essential importance that such works should be situated close to the sea, or a river, or canal, for the convenient and cheap transport of the heavy product, as it is the cost of carriage which constitutes its chief cost. The mode of separating the stone from the rock differs according to its natural formation; but in granitic and other hard rocks of continued solidity, the process, though apparently difficult, is extremely simple, as it consists chiefly in boring holes with various instruments, (which have been described, as well as the process, under the word Blasting;) then ramming into the hole a charge of gunpowder, laying a train to it, firing the train, and retreating to a distance or under an overhanging cliff to avoid the stones which are thrown up by the explosion.
The holes are made from one to three feet in depth, and generally about 1 1/4 inch diameter; hut these, as well as the position and direction of the perforation, and also the charge of the powder, are subject to the skill and discretion of the miner. The rules by which he is guided are, to direct the effort of the explosion to a part of the rock which is most easily displaced, and to proportion the charge to the effect required, so as to shake and loosen a larger portion rather.than to blow out a less quantity. The danger of beating the tamping bar with iron tools in hard rock, and the many dreadful accidents that frequently happen in this operation, have led to the introduction of contrivances to diminish the risk; but though some of these have been well adapted for the purpose, yet, as they occasion a little more trouble, they have not been generally adopted by the miner. The simplest and best precaution against danger, is to have the nail of copper, instead of iron; but as the former is not so easily made or repaired by the smiths on a mine as the latter, they are not so well liked by the workmen.
Another mode of preventing danger in tamping, is by employing substances to confine the gunpowder which require little or no force in beating them into the hole; and as dry sand will often serve the purpose if the rock is not very hard, it may be sometimes used; but there are many cases in mines where it will not succeed, and therefore it is seldom attempted. A better substance to confine gunpowder in holes, it good tough clay, and this will answer in many cases where sand will fail, particularly in wet ground, or in holes that are inclined upwards; it will produce the proper effect in all but very hard rocks, and, if the men could be induced to use it, would undoubtedly tend to the saving of many lives.
An instrument, denominated by the inventor, the "Miner's Safety Fuse," was patented in 1831 by Mr. Bickford, of Tucking Mill, Cornwall; which may be briefly described as consisting of a minute cylinder of gunpowder, or other suitable explosive mixture, enclosed within a hempen cord, which is first twisted in a peculiar kind of machine, then countered or overlaid to strengthen it, afterwards varnished with a mixture of tar and resin, to preserve the combustible matter from the effects of moisture, and finally coated with whitening, or other light pulverulent matter, to prevent the varnish from sticking to the fingers, or the fuses to one another. These fuses appear, from the specification, to be very judiciously and accurately prepared, and will, we doubt not, be found of great utility in mining operations.
For facilitating the operation of boring rocks, a patent has lately been taken out in the United States of America, which is thus described in the Journal of the Franklin Institute. "A frame is made, in the centre of which an iron shaft or rod is caused to rise and fall vertically between friction rollers, so placed as to keep it in its position. In the lower end of this shaft, a socket is formed, to receive drills of different sizes. Provision is made for placing the machine vertically, by sliding pieces upon each of its four legs, which serve to lengthen them as may be necessary. The apparatus for working the shaft up and down, is formed as follows: a circular plate of iron, about a foot in diameter, has a hole in its centre, provided with a socket adapted to the iron rod or shaft, and capable of being secured at any part of it, so that the plate will stand horizontally. At a little distance from the periphery of this plate, an iron spindle crosses the frame; upon this spindle are lifters, which, as it is turned by a crank, come in contact with the lower side of the plate, and raise the shaft; friction rollers are contained within the lifters, to cause them to slide easily upon, the plate, and their action is so managed as to produce a small revolution of the plate, and consequently of the drill, at every lift."
The term quarry is likewise given to a variety of neatly formed bricks, tiles, and stones, with very level surfaces, and of diversified colours; which are employed in many parts of England, as well as other countries, for making plain and ornamental flooring. The perforated tiles employed in malt-kilns, some kinds of drying stoves, and for various other uses, receive this denomination. An improvement in the construction of quarries, applicable to kilns for drying malt, wheat, and other grain, was lately patented by Mr. Henry Pratt, (a gentleman of great skill and knowledge in such subjects,) of Bilston, in Staffordshire; the peculiarities of which may be thus briefly explained. Instead of the usual conical openings, terminating in small circular apertures in the flooring of grain kilns, Mr. Pratt forms his quarries for such purposes of cast-iron, in preference to baked clay, having oblong slots or openings at the tops of rectangular tapering holes, which are designed for the escape of the heated air.
He casts his quarries with strengthening bars projecting from their lower sides, and these bars form the sides of the tapering channels, as well as give sufficient strength with a less quantity of material than is required when the quarries are made of an uniform thickness.