DESCRIPTION OF THE MAP.
accompanying miniature map represents the general extent and form of this great coal-field, with the prominent places and points. It extends through portions of nine States, viz. :—Pennsylvania, Ohio, Mary land, Virginia, West Virginia, Kentucky, Tennessee, Georgia, and Ala bama. Its immediate boundary in Pennsylvania, not including the outlying patches, extends from Lock Haven, on the west branch of the Susquehanna, along the Alleghany range, southwest, through the counties of Clearfield and Cambria, to the Maryland line, and northwest, through the counties of Clinton, Elk, McKean, Warren, Crawford, and Mercer, to the Ohio State line at Greenville,—embracing a productive area in Penn sylvania of about 12,000 square miles, independent of the smaller outlying deposits before noticed. The prominent places near which the coal-margin passes in its northwestern border are Lock Haven, Farrandsville, De fiance, Emporium, Smethport, Ridgeway, Johnsonsburg, Warren, Tideoute, Franklin, and Greenville. The boundaries of this great coal-field con tinue from Greenville, in Mercer county, Pennsylvania, west through Trumbull, Portage, and Summit counties, Ohio, to Akron. The bound ary-line thence runs nearly south through Ohio to the Ohio River, near Portsmouth; crossing the Ohio into Kentucky, it changes its course rather more to the west, but continues in an irregular line through that State into Tennessee ; pursuing the same southwest course, it crosses the State of Tennessee half-way into Alabama. In that State, near the Mississippi line, it forms the southern boundary, and returns by the eastern margin, in a general northeast course, through Alabama, North Georgia; Tennessee, and Virginia, to the Great Kanawha, near the mouth of the Greenbrier. Soon after crossing at this point it attains its maximum breadth, and changes its course nearly north to the Mary land line.
The length of this coal-field within its productive area is 800 miles, or to its extremity at Blossburg 875 miles. Its maximum breadth from Cumberland, Maryland, to Newark, Ohio, is 180 miles. Its minimum breadth is on a line with Chattanooga across the field, where it is not, perhaps, more than 30 miles wide. The entire area is about 55,000 square
miles, which is divided among the States in which it lies in about the following ratio :— Square Miles.
Pennsylvania 12,656 Ohio . 7,100 Maryland 550 West Virginia 15,900 Kentucky 10,700 Tennessee 3,700 Alabama 4,300Georgia 170 Total 55,076 The general form of this great coal-field is that of a rude club, the handle ranging through Kentucky, Tennessee, and Alabama, and the head resting on Virginia, Ohio, and Pennsylvania.
The northern extremity terminates in five prongs, or Titanic fingers : this we have not represented on the map, since the scale is too limited to admit of this feature being portrayed; nor have we marked the prominent anticlinals of Negro Mountain, Laurel Hill, or Chestnut Ridge, which range longitudinally along its eastern margin through the southern portion of Pennsylvania, Maryland, and part of West Virginia.
The field undulates from east to west, forming six principal basins and 'five prominent anticlinals, independent of the Maryland basin. The eastern axes are more abrupt and narrow than the western, as shown in figure 4, which conveys an approximate idea of the general form of the field. The coal measures are divided by Rogers and other geologists into three or four series or groups. We do not propose to make more than two divisions, into which the coal measures are naturally divided. That is, the lower beds, under the Mahoning sandstone, corresponding with our white ash coals in the anthracite regions and the upper beds, or those above this sandstone. The lower group naturally occupies much the larger area, on the principle represented in figure 92, where it may be noticed that the lower beds occupy a much larger area than the upper ones, though the strata pitch much more abruptly in the anthracite than the bituminous • In figure 92, A, B, C, D, and E constitute the lower group of white-ash seams, as they constitute the lower group in the bituminous fields. But here they spread out in a nearly horizontal manner, and, of course, cover a correspondingly greater amount of area.