Quarrying

In thinly bedded sandstone, where vertical joints are frequent, it is often possible to separate the desired slabs and flagstones with crowbars and wedges, without drilling or the use of ex plosives. When blasting is necessary, some form of gunpowder is generally used, rather than a violent explosive like dynamite, in order to avoid shattering the rock. This, however, applies only to dimension stone. When the production of broken stone for road-making, concrete or similar purposes is the sole end in view, violent explosives are preferred.

Channeling Machines.

In limestones and marbles and in the softer sandstones, the channeling process is almost invariably employed. Channeling machines, driven by steam, compressed air, electricity, or a combination of these are used, by which ver tical or oblique grooves or channels can be cut with great rapidity to a depth of from 8 to 12 feet. A level bed of rock is cleared, and on this are laid rails, along which the machine moves opposite to the bottom of the channel cut. After the channels are cut and a row of holes drilled perpendicular to the channel—opposite the bottom of the channel cut—wedges are driven and the required blocks or cuts of stone are separated from the ledge. These cuts, frequently of great size, running 6o to 8o ft. in length, by i o to 12 ft. in depth and 4 to 5 ft. in

width in some limestone quarries, are then with the aid of the derrick power turned over on the side, after which they are drilled and split up into blocks of convenient sizes for transportation and handling. These are called mill blocks, and are usually from 3 to 4 ft. by 3 to 5 ft. in cross-section and 6 to 12 ft. in length When the beds of stone to be quarried are comparatively thin, with heavy overburden, or when to remove the whole of the overlying mass of earth or rock would be too expensive, it has been found convenient to treat the quarry as if it were a mine. and to rely upon methods similar to those practised in mining.

Since great advances have been made in both the quarrying and working of building stone during recent years, few articles will be found that are really up to date. As a supplement to the following references the reader is referred to the more recent articles on the subject of quarrying that have appeared in trade press and technical publications of this industry as the most reliable source of additional information.

See

Institution of Quarry Managers, Quarrying (Conway, 1924) ; G. C. Mance, Power Economy and the Utilization of Waste in the Quarry Industry of Southern Indiana (Indiana Univ. Studies, 1917), also the Quarry Managers' Journal (Conway). (F. J. H. M.)