The strata thus elevated, and forming the A., belong entirely to the oldest or palteozoic division of the fossiliferous rocks. Metamorphic rocks, consisting of felspathic, horn bleudic, and micaceous gneiss, and mica-slate, exist on the eastern base of these moun tains, but have not been noticed as forming part of the plicate(' strata of the A. Exten sive formations of talcose and micaceous slates, indurated clay-slates, and chloride and steatitic slates, exist in the more disturbed districts. These are highly metamorphosed members of the older fossiliferous, and must not be confounded with, though they so much resemble, the azoie metamorphic rocks.
The paheozoic rocks constitute a vast succession of fossiliferous strata, commencing with the lowest deposits resting on the metamorphic rocks, and terminating with the highest of the coal strata. Their aggregate thickness, as measured in Pennsylvania, amounts to 35,000 ft. While exhibiting a remarkable variety of mineral character, they may be classed under the three great divisions of sedimentary rocks—viz., sandstones, slates, and limestones. Intercalated with them, as subordinate layers, there occur deposits of coal, chert, and iron ore. They are all more or less fossiliferous.
Coal character of the rocks of the Appalachian district of North America indicates that during time carboniferous epoch an immense continent existed on the present site of the Atlantic, which supplied materials for the sandstone and slate. It seems to have had an extensive shallow marshy shore, of such a character as to be able to support the vegetation, which has become, in the course of ages, converted into coal. The coal-fields to the far w. of the A., in Michigan, Indiana, Illinois, and Mis souri, have been connected with the Appalachian coal formation, which includes all the detached basins, both enthraciti• and semi-bituminous, of the mountain chain of Penn sylvania, Maryland, and Virginia, and also the vast bituminous trough lying to the n.w. in Pennsylvania, Ohio, Virginia, Kentucky, Tennessee, and Alabama.
On the eastern slope of the A., the coal, from its proximity to the region of greatest disturbance, has lost nearly all its volatile constituents, and is converted into hard shining anthracite (q.v.). In the troughs to the westward of the great Appalachian valley, where
the forces that disturbed the crust were not so intense, the coal has not parted with such a large proportion of volatile Matter, but still is so much altered as to be characterized as setni-anthracite. Both the anthracite and semi-anthracite are extensively mined for economical purposes, but their extent as well as their value is of little importance com pared with the enormous Appalachian bituminous coal-field. From northern Pennsyl vania to middle Alabama, its length is about 875 m., and its greatest breadth between southern Pennsylvania and northern Ohio is about 180 m.; it covers an area of about 56.000 sq.m., and is almost the largest expanse of coal measures in the world. A single coal-seam iu this field has been traced over an extent of country 225 m long, by 100 broad, showing a superficial area of 14,000 sq.miles. The actual depth of workable seams in the deepest part of this basin is estimated at 40 ft.; but when the amount of denudation of the upper measures over large districts is taken into account, the average depth of the entire field cannot be more than 25 ft. Taking this as the thickness, the amount of coal in this great coal-field would be 1,387,500,000,000 tons. When this is compared with the estimated quantity of coal in the British coal-fields, viz., 100,000,000,000 tons, some con edition may be formed of the enormous extent of coal existing in this district of North America.
Metals. —Extensive beds of magnetic, hematitic, and fossiliferous iron ores occur in many of the formations of the A., from the lowest metamorphic gneiss to the highest coal-measures. Iron ore is extensively wrought in Pennsylvania and Ohio, large quanti ties of the anthracite being used in time smelting furnaces. Veins of lead occur in the metamorphic rocks, rarely stretching up into the red slate. In the pakeozoic beds, veins of copper and nickel occur in sufficient quantity to be wrought.