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Process of Obtaining Coal

Where coal is within easy reach from the soil, it is often " stripped " and quarried. Usually, however, its depth obliges us to excavate or burrow after it, to mine it. Mining coal in some countries is being done at over half a mile deep, but in this country coal at present is so abundant that we can obtain all we require without going deeper than a few hundred feet. To reach it, tunnels are driven into the hillsides, " slopes " or inclined places are sunk, or vertical shafts dug down to it through the rocks.

There are two methods in general use for taking out coal, but modifications of both, to suit special conditions and locations, are sometimes adopted. One plan is to mine it in narrow places called "rooms," leaving thick walls or pillars of solid coal to support the tunnels and other passageways, as well as the overlying strata, until the limits of the mine are reached, and then to remove most of the pillars and let the top cave in. This is called the "room and pillar" system. The tunnels are driven in pairs, about six hundred feet apart, and about three hundred feet of coal in width is removed from each side so long as the coal-bed lies nearly flat ; but when it slopes considerably the coal is only taken out on the upper sides of the tunnels or "gangways," and these are then driven much closer together. As they serve for drains as well as transportation and travel, they are usually driven nearly level. The "rooms" are made about thirty feet wide and the pillars left about fifteen feet wide. In level regions the directions in which the coal is opened up and mined away are very largely governed by the direction of the principal natural joints or "cleavages" by which many coal-seams are very persistently and remarkably evenly divided or split up. The miner uses these joints to save himself labor, as well as to produce the coal in its best condition and greatest quantity. If the coal is strong and tenacious it is detached from its bed by blasting, after being partially set free by undermining it. This process is done by picks or by machinery. When by the latter nearly half the miner's labor is saved. In steep mine-workings the miner takes down the coal in rooms, standing upon timbers or upon the broken coal below him; which is drawn off through gates on the levels and carried away as fast as fresh coal is mined. The removal of the pillars and emptying of the coalfilled rooms go on together.

The other plan of coal-mining is to take out all of the coal in advance, or, as you work away towards the boundaries of the property, tearing down so much of the overlying strata as you advance, and with it building rough walls on each side of every gangway or road in order to maintain them through the broken and squeezed-down roof, following the removal of the coal. This plan is known as the "long wall " method. When the " top " is a yielding one, the "floor" soft, and the seam thin, this method is preferable to the pillar plan. To detach the coal from the seam, it is first secured by wooden props, then undermined with pick or machine; and when the timbers are knocked away, the weight of the exposed coal and the tendency of the roof to squeeze it down, usually breaks it off in large, long masses, easily broken up, cleaned and loaded into cars. The roadways are made about fifty feet apart in low coal, and about one hundred and sixty feet in higher seams, where the mine cars travel along the "working-faces." A miner produces from two to eight tons for a day's work.