Mining

the business of obtaining useful minerals from the earth's crust. Most minerals are found in a more or less horizontal layer called a stratum, bed, or seam. Sometimes several strata, separated by intervening layers of earth or rock, occur together. When for any reason the mineral stratum is at the surface of the earth, mining is a simple operation. Sometimes river valleys have cut through many strata exposing those in which minerals are found. In such a case, galleries are excavated through the mineral vein, enough of the mineral being left in places to support the overlying weight of earth or stone. Ordinarily, however, it is necessary, first of all, to send down a central shaft from which passages are constructed in various directions. The mineral is brought to the shaft on underground tramways and is hoisted to the surface. In the case of vertical mineral veins, a sloping shaft is not infrequently constructed.

A tin mine in Cornwall, England, extends far out under the sea. One of the deepest mines in the world is the North Tamarack copper mine in upper Michigan. It lacks eighty feet of being a mile in depth. The Red Jacket shaft of the Calumet and Hecla is down (1905) 4,900 feet. The most extensive as well as the most curious mines in the world are the famous salt mines near Cracow, in Austrian Poland. For ease of working the surface iron mines of northeastern Minnesota are unexcelled.

Mining is one of the most ancient occupations. Mining engineering is a distinct profession in itself. The engineer requires to have a knowledge of mathematics, mechanics, physics, and mineralogy. Special schools of mining engineering have been established. One of the most famous is maintained at Freiberg, Saxony. The earliest school of mining in the United States was established at Columbia University. Similar departments are now maintained in leading colleges and universities.

Half a million men are employed in the mines of the United States and about 50,000 in Canada. The total mineral output of the United States for 1901 was valued at $518,000,000. In 1907 the value had increased to $2,069,289,196--nearly four times as much. Pennsylvania alone is credited with a greater mineral output than that of the entire Union in the former year. The mineral output of Canada for 1902 was valued at $65,000,000; for 1907, $86,000,000.

See Copper; Coal; Iron; Gold; Silver; Lead; Nickel; Salt; Safety Lamp; Mineral Products