point lateral openings are driven into it and extraction begins. Coal mining once required much human labor. Holes were drilled into the face of the coal seam and loaded with black powder or dynamite, and the explosions spewed up broken coal which was then loaded by hand-shovel into a small car. When full, this was pushed by men or pulled by a mule along a track to a loading pocket adjacent to the shaft. The coal was then loaded into other cars or buckets and hoisted to the surface. New technology has changed this picture. The continuous mining machines are powered by electricity, and they cut out the coal instead of blasting, break it, and convey it continuously into waiting cars for transport to the hoisting shaft. Such mines are rarely three thousand feet deep; they range from a few tons of daily production to ten thousand tons; and they employ one to two thousand men in individual mines.
Another form of mine is the strip mine, created by stripping the overlaying material, called overburden, from a minable coal seam. Draglines or large electric shovels are used for this purpose; in either case, the overburden is stacked behind the current operations on the recently mined-out area of the pit so that it can be leveled or landscaped again. The coal bed is blasted to break it for shoveling. Drill holes are now made a foot in diameter and the explosive material, ammonium nitrate, is chemically and physically more like fertilizer than dynamite. A shovel or front-loader is used to place the broken coal on trucks. Most such mines are less than two hundred feet deep, and they may produce as much as fifteen thousand tons of coal a day, employing as many as seven hundred men in a single mine. More than half the coal produced in the United States is produced from strip mines.
The third method produces very little coal in the United States -- auger mining, which is carried out by means of large horizontal augers that bore i...