A relatively small amount of coal is quarried near the surface of the ground from open pits. The overlying soil is removed by steam-shovels, and the coal is then blasted out and shoveled into cars.
Most coal is mined underground. Access to the coal-beds is obtained either by sinking a vertical “shaft” or by driving a tunnel, according to the location of the beds. A tunnel driven at a steep angle is called a “slope.” A horizontal tunnel leading into a coal-seam is called a “drift.” In this country few coal mines are more than 300 or 400 feet below the surface, and the deepest is about 1,600 feet. Much deeper mines are found in Europe, especially in Belgium.
[Illustration: Press Illustrating Service
Showing a coal car half turned over in order to dump contents]
which, by rotating motion, separate the coal from slate]
[Illustration: Courtesy of U. S. Bureau of Mines
Of fireproof construction. Anthracite coal mine]
American mine shafts are generally rectangular and are divided into two or more compartments. Where a shaft passes through water-bearing strata it must be provided with a tight lining, or “tubbing,” to prevent the mine from being flooded. All water that enters the mine collects in an excavation, or “sump,” at the bottom of the shaft, and must be pumped to the surface.
The method of working coal-seams most commonly practiced in this country is known as the “room-and-pillar” system. One or more tunnels, or “entries,” are first driven from the bottom of the shaft or the mouth of the drift. These are the main thoroughfares of the mine, and are usually provided with tracks, over which the mine cars are hauled by mules or by some other method of traction--locomotives, endless chains, etc. Secondary entries (“headings,” “butt entries,” etc.) branch off from the main entries. Finally, the work of extracting the coal consists of excavating open spaces, or “rooms,” adjoining the entries.
Note the neat and careful “upkeep” of the place]
The actual mining is done in the rooms, and different methods are in use. Anthracite is generally “shot from the solid”; that is, blasted out from the face of the coal without any preliminary cutting. This method is objectionable, especially in bituminous mines (where it is, however, much practiced), because the large charges of powder it requires produce a great deal of coal-dust and weaken the roof and pillars, often leading to falls of coal and fatal accidents. A better plan consists of “undercutting” the coal before it is blasted out. A long groove is made at the level of the floor, either with a pick or with a coal-cutting machine. Holes are then drilled some distance above the groove for the insertion of the blasting charges, and the coal is blasted down. A single shot will sometimes dislodge a ton or two of coal.