MINING. is a basic industry, the magnitude of which is indicated by the 6,000,000 men employed in the various mines in the world. Of this number about 3,800,000 men are en gaged in coal mining and 2,200,000 in other mining. In addition millions are employed in the allied industries, such as the manufacture of iron and steel, copper wares, coke and chem icals, all of which are directly based upon the industry. The mines and quarries of the United States in 1917 employed over 1,127, 000 men segregated as follows: Coal mines, 757,000; metal mines and metallurgical works, 280,000; quarries 90,000.
Geographic bistribution, The mining in dustry of the United States is roughly geo graphically distributed as follows: The an thracite coal mines are in northeastern Pennsyl vania the bituminous coal mines occupy the western slope of the Appalachian Mountain system from northern Pennsylvania to north ern Tennessee, with a large coal field in the vicinity of Birmingham, Ala. The central coal field occupies central and southern Illinois, southwestern Indiana and western Kentucky. The coal fields west of the Mississippi River include southern Iowa, northern and western Missouri, southeastern Kansas and northeast ern Oklahoma, with large bituminous and lig nite fields in Texas. The coal fields of the Rocky Mountain States are scattered with the principal fields in southern Wyoming, northern Wyoming, western Montana and northeastern Nro• Mexico and southeastern Colorado. The Pacific Coast States coal fields occupy the north western part of Washington with a small area m western Oregon and a small field in Cali fornia. Alaska has coal fields in the southern portion which are of considerable importance, although not well developed. The United States is the greatest producer of coal, and in normal times the yield is 38 per cent, Great Britain 22 per cent and Germany 20 per cent of the world's output of coal. The metal-mining in dustry of the United States is distributed ap proximately as follows: The principal iron mines are in Minnesota, Michigan, northern Wisconsin, northeastern New York and central Alabama. The principal copper mines occur in northern Michigan, western Montana, Utah, Nevada, Arizona and southern Alaska. The lead mines are in southeastern Missouri, the Coeur d'Alene district, Idaho, and in Colorado. The principal zinc mines occur in southwestern Missouri and eastern Oklahoma; Leadville, Colo., and Butte, Mont., are becoming large
producers. The gold and silver mines occur in Alaska, California, Colorado and Nevada, while every Rocky Mountain and Coast Range State produces more or less of the precious metals. Phosphate rock occurs in large quanti ties in Tennessee, Florida and South Carolina; bauxite in Arkansas and Georgia; salt in New York, Michigan and Kansas; petroleum and natural gas in Oklahoma, Texas, California, Pennsylvania, Ohio, West Virginia and In diana.
The United States is the world's largest pro ducer of copper, iron, lead, zinc and petroleum. About 20 per cent of the world's gold supply comes from the United States; 40 per cent from South Africa and 15 per cent from Australasia. (See article on GOLD MINING). The Central Powers of Europe produce only 0.6 per cent, while the United States and her allies produce 91.3 per cent, and neutrals (1918) produce 8.1 per cent.
Preliminary work in mining operations is known as prospecting, and is often conducted by individuals who work on their own account, spending weeks or months in out lying districts in search of mineral outcrops or rock indicating that valuable minerals may be present. The prospector of the early days is fast disappearing and prospecting is now carried on in a scientific way by large develop ment or exploration companies, whereby a promising mineral field is thoroughly tested by churn drills or core drills as economy may suggest. The core or diamond drill is most im portant in this particular work in that it obtains a core so that it is possible to know accurately the formation through which the drill has passed together with its thickness, depth and mineral content. The ground is marked out in squares of 100 to 500 feet on a side and at the corners or in the centre of each square a drill hole is sunk, and the core or cutting thor oughly tested. This work is carried on in conjunction with geological studies, in which the character of the various country rock is studied, as, for example, its position and com position, lithological character and other data which may be of interest to the prospector and geologist, and help to point out the places where ore deposits are most likely to occur. Trenches are often cut across mineral zones, and small shafts sunk to test the character and quality of the mineral.