The bituminous coals of the Appalachian field include gas, coking and steam coals of the highest grade. The largest and best seams or those most easily opened have been exploited so far, and the resources of the Appalachian field are still enormous. The State of West Virginia alone is estimated to contain more workable coal than the whole of Great Britain. The best-known of the various areas now opened are the Clear field, in Pennsylvania, producing coking, gas and steam coals, shipped largely to seaboard points ; the Broad Top, in Pennsylvania, pro ducing coal of rather better grade, shipped to the same markets ; the Cumberland, in Mary land, producing a famous steam and smithy coal, shipped to the seaboard and to interior cities from Canada to the Rocky Mountains; the Pittsburgh, in Pennsylvania, whence come gas and steam coals largely used locally, but also shipped to points on the Great Lakes and on the Ohio River and lower Mississippi; the Connellsville, in Pennsylvania, yielding coal used chiefly for making a standard grade of coke; the Hocking Valley, in Ohio, whence are shipped steam coals to near-by cities and to distant ports on the Great Lakes; the Kanawha, in West Virginia, shipping gas and steam coal to various points on the Great Lakes or on the Ohio River and lower Mis sissippi; and the New River, Flat Top and Pocahontas fields in West Virginia, produc ing steam, gas and coking coals of varying excellence, the best grades having no superior, which are shipped mostly to seaboard points, though an increasing tonnage is made into coke to supply blast furnaces at Pittsburgh, Chicago and various Ohio cities. In eastern Kentucky is the Jellico field, whence gas and steam coal is shipped to a wide territory, in cluding seaboard cities, and in eastern Ten nessee are several basins yielding gas, steam and cooking coals, used locally and shipped to compete with the Jellico coal. The import ant district in Alabama is about Birmingham: the coal is shipped to Atlantic and Gulf ports for steam- and gas-making, and a large propor tion of the output is made into coke for use in local furnaces and foundries.
The eastern interior field covers western Indiana, nearly the whole State of Illinois and part of Kentucky. The coal is of Carbon iferous (Pennsylvania) Age, but in general lies in thinner veins and is of poorer quality than that of the Appalachian field. Most of the output is used as a steam fuel by rail roads and in the many manufacturing cities that lie in or near the field. Certain grades are much used as a household fuel. The field contains no first-class coking coal.
The northern interior field covers a large area in the southern peninsula of Michigan and has been opened chiefly by the mines near Bay City and Saginaw. The seams are comparatively thin, and the coal is generally of poorer quality than that of Indiana and Illinois. The output is used locally. The beds are of Upper Carboniferous Age.
The west central field extends from west ern Iowa across western Missouri and into northwestern Arkansas and eastern Nebraska and Kansas, through Oklahoma into Texas. The coal beds vary widely. In parts of the field the coal is barely more than lignite, while in northwestern Arkansas it approaches semi-anthracite. The markets supplied cover a great area. Fully half of the output is used by railroads, and of the other half at least 40 per cent is used for household purposes. The measures are Carboniferous.
The Rocky Mountain field includes the numerous disconnected areas lying in narrow belts along either flank of the range from the Canadian frontier southward for 1,000 miles; Montana, Utah, Wyoming, Colorado and New Mexico having mines. Along the
flanks of the mountains and in the parks or plateaus in the main range the coal is largely bituminous ; but eastward from the range the coal measures, which are of Upper Creta ceous (Laramie) Age, are lignitic, and vast beds of lignite underlie the plains of Montana, Wyoming and North and South Dakota. The mines now opened supply the great trans continental railroads, the chief users. In places the coals make good coke, used by local smelting plants. The resources of the field are vast and but little developed.
The Pacific Coast coal field is of Tertiary Age and most of the output is lignite. It in cludes some unimportant basins in California, several fields in Oregon, of which the Coos Bay has been most developed, and the Roslyn and Puget Sound fields in Washing ton, the former producing. a good bituminous colcing coal. The California and Oregon fields are of little more than local importance, but the Washington mines supply railroads and steamships and are an important factor in the coal trade of San Francisco.
The rank of the principal coal-producing States is shown by the following table compiled from figures published in the 1915 report on the °Production of CoaP prepared by the United States Geological Survey: The coal reserves of the United States lying not deeper than 3,000 feet are estimated at 3,350,000,000 tons; 1,000,000,000 being in the Appalachian fields and 2,350,000,000 in the Roclcy Mountain and Great Plains fields. Up to the close of the year 1916 the output of all the mines was in round numbers, 11,500,000,000 tons, and as half a ton of coal is wasted for every ton produced and sold, it is estimated that the total exhaustion of the country's coal fields to the date cited amounted to 17,250,000,000 tons. As compared with the amount of coal existing in all the United States fields, this exhaustion amounts to one-half of one per cent of the supply; and, at the present rate of use there is coal enough underground to supply the country for about 4,000 years to come.
The coal being consumed at present in the United States comes: from the anthracite fields of Pennsylvania, 70 per cent; from the bitu minous coal area of the Appalachian area, 20 per cent; and from the great Western fields, 10 per cent. Although the anthracite area in the northeastern part of Pennsylvania is less than 500 square miles, it has yielded in the aggregate 2,626,500,000 tons, and it is estimated that four times that quantity remains un touched. Fully 70 per cent of the country's coal lies west of the Mississippi, but it is mostly of semi-bituminous and liiznite grade. The high grade bituminous coal of the Appa lachian area is being exhausted more rapidly in proportion to the supply than even the very limited anthracite deposits, and geologists assert that its complete exhaustion is not far off. See FUELS.
Arber, E. A. N., 'The Natural History of Coal' (Cambridge 1911) ; Campbell, M. R., (Map of the Coalfields of the United States: with Notes) (U. S. Geological Survey Office, Washington 1908) ; Gibson, W., 'The Geology of Coal and Coal Mining' (Lon don 1908) ; International Geological Congress XII, (The Coal Resources of the World) (3 vols. and atlas); Kent, W., (Steam Boiler Economy) (London 1915); Somertneier, E. E., (Coal: Its Composition, Analysis, Utilization and Valuation) (New York 1911) ; U. S. Geo logical Survey, 'Mineral Resources of the United States) (Washington—annually); Wagner, F. H., (Coal and Coke) (New York 1916).