Page:The American Cyclopædia (1879) Volume IV.djvu/755

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739
COAL

of its constituents; it merely quickens the slow burning or metamorphosis of the matter, the ultimate result of which is the entire reduction of the oxygen- and hydrogen-producing volatile gas into compact or condensed mineral combustible, a mere compound of the original elements of wood modified under peculiar influences.—The great Alleghany coal field extends from the middle of Alabama to northern Pennsylvania, and occupies portions of Alabama, Georgia, Tennessee, Kentucky, West Virginia, Virginia, Ohio, and Pennsylvania. It contains from 50,000 to 55,000 sq. in. of coal area, and all the coal beds and groups of beds described under the title Anthracite, the nomenclature of which will be adopted herein. In some portions of the anthracite fields the millstone grit or conglomerate is interstratified from the bottom to the top of the coal measures, though much more massive near the bottom than in any other portion. It is also much thicker in the eastern part of these fields than in the western portion, and likewise more massive than in the bituminous fields, or westward generally, as the foregoing table indicates. A group of coal beds, O, not shown in the anthracite column, though existing there as “nests” of imperfect coal below A, are found AmCyc Coal - Alpha group.jpg
A, or Alpha
at irregular intervals throughout the Alleghany coal field; but these beds are thin, impure, often absent, and rarely of workable size or merchantable quality. They exist both below and in the millstone grit when found, and are more persistent and regular in the western than in the eastern coal fields. The first group of regular beds is A; these also exist in the conglomerate in the Pennsylvania anthracite fields, and in some of the outlying basins of the Alleghany field; but generally they consist of two small, unworkable streaks of impure coal, or a single bed of earthy coal 1 to 4 ft. in thickness, resting on or near the millstone grit. It produces the block or AmCyc Coal - Buck Mountain group.jpg
B, or Buck Mountain.
furnace coal of Pennsylvania. The next group, B, consists of two regular and excellent beds, which are generally united as a single bed, though always divided by a streak of slate or fire clay, which often expands to 20 ft. or more. This bed, or group of beds, is the most regular of all the American coal beds; and, being the first large, workable, and productive bed, its horizon is the most extensive, and nearly equal to the area of the entire field, while it can readily be identified in the central if not the western coal field. These beds, when united, are from 4 to 7 ft. thick, and singly from 2 to 4 ft. each. Immediately above this group, sometimes resting on the coal, but generally separated by slates and shales, is the micaceous sandstone, or “buckwheat rock” of the Pennsylvania mines, which is a coarse, massive sandstone, filled with mica scales. This rock is very persistent, and can be identified in all the great American coal fields of the carboniferous age. This great bed of sandstone, which is often 20 to 60 ft. in thickness, is followed by shales and the fossiliferous or ferriferous limestone, and the AmCyc Coal - Gamma group.jpg
C, or Gamma.
buhrstone iron ore, which are generally present in the Alleghany coal measures. The ore ranges from 10 to 20 in., and the limestone from 10 to 20 ft. in thickness. This is succeeded by shales and the group of coal beds.C. In the anthracite regions, and generally in the bituminous fields, this group consists of two thin, slaty, and AmCyc Coal - Skidmore group.jpg
D, or Skidmore.
unworkable beds; but one of them frequently expands to 3 and even 5 ft. of excellent splint or cannel coal. It is the celebrated Peytona cannel bed of Coal river, West Virginia, and the Grayson cannel of Kentucky. This group is succeeded by shales and sandstones of variable thickness, from 50 to 150 ft., on which rests the bed D, which is always single, and generally pure and workable, from 30 in. to 4 ft. in thickness. Above this bed, separated by AmCyc Coal - Mammoth group.jpg
E, or Mammoth.
sandstones and shales, is the Curlew or Freeport limestone, 8 ft. thick; and on or near this rests the group E, which embraces two or three beds of coal, each generally from 2 to 4 ft. thick, which often unite as a single bed of 6 to 12 ft., divided by slates. This group forms the celebrated mammoth bed in the Pennsylvania anthracite fields, and the Freeport beds in the western part of Pennsylvania. Above this group (which is very confusing to the miner and the geologist, on account of its irregularity and uncertainty in uniting and dividing) from 20 to 50 ft. of soft black shales or slate are generally found, and on these rests the Mahoning or mammoth sandstone, which is the largest regular sand rock in the Alleghany coal measures, ranging from 50 to 75 ft. in thickness, divided by one and sometimes two thin coal seams, and several feet of slates or shales. Streaks of quartz crystals are often found between the upper and lower strata of