UNITED STATES. The coal-fields of the United States are especially extensive; indeed, in sonic instances the deposits of a single State exceed those of Germany or France in area. They are separable into several regions, the divisions being geographical and not geological. The geological ages of the coals in 1, 2, 3, 4, and 6 (table on next page) are all Carboniferous, except small Triassic areas in Virginia and North Carolina. Those of 5 are Cretaceous and Tertiary.
By far the most important of these regions is the Appalachian, which takes in portions of Penn sylvania, Ohio, \Vest Virginia, Virginia, Maryland, Eastern Kentucky, Eastern Tennessee, Georgia, North Carolina, and Alabama. It is about 750 miles long, and 70 to 80 miles wide. The coals are all bituminous or semi-bitmninons with the exception of those at the northeastern end, in Pennsylvania, where close folding of the rocks has changed the bituminous into anthracite coal. In general, the rocks at the upper or northern end of the Appalachian belt are folded, while those of the lower end, as in Alabama, are often faulted in addition, so that the coal-miner fre quently finds the coal-seam suddenly broken off. The Carboniferous section of this region has among three districts—the Warrior, Cahawba, and Coosa, named after the rivers that drain them. The anthracite district of Pennsylvania, occupies an area of about 470 square miles on the lest bank of the Susquehanna. The strata between Potts ville and Wyoming, which belong to the lowest portion of the coal-measures, are probably about 3000 feet thick; but it is difficult to make an exact estimate, because of the numerous folds and con tortions. There are from 10 to 12 scams, each over three feet in thickness. The principal one, known as the Mammoth or Baltimore vein, is 29 feet thick at Wilkesbarre, and in some places exceeds even 60 feet. Many of the Appalachian coals, notably those of western Pennsylvania, West Virginia, and Alabama, produce excellent coke. The Ohio coals do not yield good coke. In most of the other coal-fields of the country the coal-beds lie comparatively flat, and the basins are quite shallow.
The Michigan area is a small one in the lower peninsula of Michigan. It forms a circular basin with a diameter of about 50 miles. The coals are bituminous, non-coking, and are mined chiefly for local use. The seams range from a few inches to three feet in thickness.
The Central area includes parts of western Kentucky, Indiana, and Illinois, and lies chiefly within the latter State. These coals are all bituminous, of Carboniferous age, and are used chiefly for steaming. The thickness of the Car
boniferous System varies from 1200 to 1400 feet in southern Illinois, to about 600 feet in Indiana, and the workable coal-seams vary in number from 7 to 12 in Illinois, and their thickness from three to eight feet. The 'block coal' of In diana has quite a reputation. The Western Central area includes Iowa. Missouri, Arkansas, Indian Territory, Kansas, and part of Texas. Pere again there is an abundance of bituminous coal, which has been developed chiefly in Iowa and Missouri. while Kansas is now coining into prominence. The coals of this area are chiefly adapted to smithing and steaming purposes, and, so far as tried, Kansas yields the only coking varieties.
been described in the article CARBONIFEROUS SYSTEM, from which it may be seen that the coal beds occupy more or less well-marked strati graphic positions. The maximum thickness of strata is from 2500 to 3000 feet ; the seams meas uring 120 feet near Pottsville, 62 feet at Wilkes barre, and 25 feet at Pittsburg, showing a gradual diminution in a westward direction. The most persistent coal deposit is the Pittsburg seam, which is known over an area measuring 225 by 100 miles, and has a thickness varying from 2 to 14 feet. In Alabama the deposits are distributed The Cordilleran area comprises the coal regions of Colorado. New Mexico, Utah, Wyo ming, South Dakota. North Dakota, Montana, California, Oregon. and Washington. In this field are found many varieties grading between lig nite and anthracite. They are all of either Tertiary or Cretaceous age. and their discovery showed the incorrectness of the old classification, which included all post-Carboniferous coals under lignite. Colorado is perhaps the most important producer, having a number of good bituminous seams. Those in the vicinity of Crested Butte have been changed locally to anthracite by the metamorphic action of igneous intrusions. Excellent coking coals are found near Trinidad. The New Mexican coals are in part an extension of the Colorado veins, and hear a good reputation, as do also many of the Wyoming coals. California has little fuel of good quality, and has for many years drawn on Australia for its coal-supply. but in recent years the coals of Oregon, Washington, and British Columbia have become a source of supply.
The rocks of the small Rhode 'Island area have been so highly metamorphosed that the coal has been altered to graphitic anthracite. It is sold on the market as amorphous graphite, and has little value as a fuel.