Coal is broken from the face of the seam by the miner under-cutting it with his pick and then putting in a blast strong enough to bring down the coal. Black powder is generally used in this country. Abroad explosives making less flame are required by law in many districts, and in some of the very fiery German mines wedges operated by hydraulic power are used. Blasting, or °shooting off the solid,° is prac tised extensively, entirely in some sections, 15 per cent of the total production being so mined in 1915, but it is considered a wasteful and a dangerous method, as it not only causes cave ins, but shatters the coal. Fine coal is less valuable than lump, and dust greatly increases the danger of an explosion.
To under-cut the coal, machines are some times used. Those in general use in this coun try are of two types: the Harrison, or puncher type, with a reciprocating piston impelled by compressed air, carrying a cutting bit; and the chain machine, having an electrically driven chain carrying cutting teeth. The latter type, though not favored for fiery mines, is probably more used in newly opened mines, than the former. No machines are used in the Pennsyl vania anthracite mines. Of the total bitumi nous coal (442,624,436 tons) mined in the United States in 1915, 243,237,551 tons were under-cut by machines.
There has been a steady tendency toward the increasing use of machinery. In 1903 only 27.6 per cent of the total production of bitumi nous coal in the United States was machine mined. In 1910 it had increased to 41.7 per cent and in 1915 it was over half —55 per cent. In that year 15,692 machines were in operation in the coal mines of the country, dis tributed (in part) as follows: Pennsylvania, 5,935; West Virginia, 2,479; Illinois, 1,787; Ohio, 1,459; Kentucky, 1,399; Indiana, 660; Ala bama, 373; Colorado, 299.
Recently steam shovels have been employed in mining bituminous coal in Kansas, Oklahoma, Missouri, Indiana and Illinois, where there are areas of flat-lying coal veins near the surface. Some of these shovels have a dipper capacity of eight cubic yards.
The coal when broken down, is roughly sorted by th'e miner or his helper and loaded into mine cars which are hauled to the main haulage roads by mules. Here the cars from the various gangways are usually made up into trains (or utrips°) and hauled to the shaft bot tom or the entrance of the mine by a wire rope (tail-rope haulage), by a compressed air loco motive, or by an electric locomotive. Some times the cars are attached singly to an endless wire rope like cars on an ordinary surface cable road (endless-rope haulage). Mines. of the shaft type are to be found in largest numbers in the hard-coal districts. The hard-coal mines are likewise the deepest. Occasionally an ex treme depth of 1,500 feet is attained. Two other styles of mines are found in both anthracite and bituminous fields,—udrifts° and °slopes.° The
drift mine is dug straight into the mountain from one side. The passageway or heading may have an upward trend. The slope mine slants downward to the extent of perhaps 35 or 40 degrees, the main heading often measur ing a mile or more in length.
An interesting process also is °pocket min ing,° but this is practised comparatively little to-day. An outcrop of coal at various points on the side of the mountain suggests the pos sibility of a rich mineral vein. Digging is be gun directly into the bed of coal projecting at the surface. This form of mining is seldom highly profitable, for when the digging has progressed at considerable expense to a point where the mine should be expected to pay, all operations are suddenly cut short by the en countering of solid rock, which, owing to some upheaval of the past, has °faulted" the vein of coal from its natural course. These pockets at intervals in the mountains where pocket mining is done present an interesting sight. About Shickshmny, Pa., they are numerous.
In shaft mines, and especially those of an thracite, mules are used very extensively. Where mechanical power is employed to haul trains in the main haulage-ways, these beasts bring the cars only from the side headings or the rooms. The mules do not see daylight for months at a time. In bituminous drift mines evolution has included the introduction of min iature trolley trains of 40 or 50 cars, each train being in charge of a motorman and brakeman. In anthracite drifts steam locomotives of a small and peculiar type, known as °hogs," haul the trains. In a slope mine cable trains trans port the coal. One end of the cable is attached to the train, and the other winds upon a drum at the power-house. When the cable turns a corner it passes around what is known as a °bull wheel.° Twenty-five one-ton cars may comprise a cable train of soft coal. Anthracite cars often hold four and a half tons. In soft coal mines the man in charge of the cable train is called a °rope rider.° In bringing his cars out of the mine he sits upon the nng which connects the cable with the train. In the an thracite slopes a man stands upon the side of a car ready to usprag° the wheels when a stop is made. Spragging consists in throwing short but stout lengths of wood into the openings between the four spokes of the car wheel. The height of the bituminous vein is often not more than four or five feet, thus making the quarters of the miners rather cramped. In the mining ot anthracite only two-thirds loosened from the vein is of value. The miner must use good judgment in loading only the paying coal. To handle and transport chtmlcs in which slate pre dominates is unprofitable. Even the better coal has more or less slate in it, while in bituminous coal the slate is pnncipally at the top and bot tom of the vein and not mixed with the prod uct as mined.