THE ALLEGHANY COAL-FIELD IN OHIO.
The coal-area of Ohio has been variously stated at from 5000 to 12,000 square miles. We have taken it at 7100 square miles productive coal-area, which will be its maximum, though the coal measures, including the Carbo niferous limestone, extend over one-third of the State. But Ohio is, perhaps, as much diversified and cut by streams as West Virginia, though they are less in volume and length. Those within the coal-field generally rise towards or even beyond the outcrop of the coal, and flow towards the Ohio, down the dip of the measures.
All the streams feeding the Ohio, except the Great Kanawha and the Tennessee, rise within the margins of the Alleghany and the Central coal fields. Most of them, however, rise within the Alleghany. The Ohio River flows nearly through the synclinal axis of the Alleghany basin from the great bend below, and yet north of Pittsburg, to the mouth of the Guyandotte; while the upper waters of the Ohio—the Alleghany, Monon gahela, &c.—rise within the vast area that fills Western and Northwestern Pennsylvania, and descend towards the centre of the basin from the high plateaus of the Alleghany Mountains, the eastern escarpment of which forms the Atlantic margin of the great basin as it now exists.
The western margin of the Alleghany field is much lower than the eastern, and consequently the length of the eastern-dipping strata is correspondingly less than the western dip. The coal east of the Ohio has a general and gradual dip towards the Ohio; but the coal on the west of this river has a corresponding but reversed dip towards it as a common centre: the streams follow, as a general rule, the inclinations of the strata over which they flow.
The highest portion of Ohio is lower than the outcrops, or eastern margin of the Alleghany field on the plateaus of that range; while the valley of the Ohio is much lower, of course, than the elevations of that State. Yet a large portion of Ohio, having its horizon on a common level with the most productive portions of the Alleghany and Central coal-fields, is destitute of coal or coal-bearing rocks. We can only account for such a deficiency by the theory of depression, or that of denudation. The last will not stand a critical examination, since it is not possible that an entire formation could have been swept away by water without leaving some relics of its former existence. But we have seen that a gradual depression of the interior of this great basin must have taken place during or after the formation of coal: we must, therefore, presume the area in Ohio, which is now destitute of coal, to have been above water during its formation.
It is evident that the interior of the great basin lying within the Alle ghany and Rocky Mountains must have been at one time a vast lake or inland sea, having no connection with the great waters of the globe as they now exist. All the rivers of the Great Mississippi Valley take their
rise within this basin as it now exists; though the Tennessee and the Kanawha, on the east, extend beyond the rim of the Alleghanies, which form the natural boundary of the present basin to the east.
This exception, however, is accounted for by the fact that the ancient granite boundary of this vast inland water was not so much depressed in the quarter where the Kanawha and Tennessee Rivers take their rise, as this granite rim was depressed both farther north and south.
The final depression of not only the granite rim or boundary of the ancient sea, but the entire Palozoic structure formed in that sea to the south, effected its drainage into the Atlantic Ocean; but the depression of the interior or central portion was beneath the level of the Atlantic, form ing the waters of the Gulf. Before this drainage was effected, certain portions of the great basin must have been above water-level; and that portion of Ohio which does not contain the coal measures must have been one of these dry spots or islands. That portion drained into the Lakes is outside the borders of the coal-field, and geologically below the level of our coal formations, and beyond the influence of those conditions, formerly described, which must exist in order to produce coal.
In the case of the denuded portions of Indiana and Illinois, along the Wabash, we have evidence of the former existence of coal; but over the space which adjoins the non-carboniferous portions of Ohio the former arguments hold good. The great coal-fields, however, which lie to the west of the Alleghany field, formerly existed, in all probability, in an unbroken body. That portion of the Great Central field which lies in Indiana and Kentucky is only divided from Illinois by the valleys of the Wabash and Ohio Rivers, and we cannot doubt its former existence as a whole. We have, therefore, given it as a neat coal-field, under the name of the " Central;" and this title may apply with equal propriety to the coal-field in Missouri and Iowa, which is only divided from the Central by the Mississippi, and the denuded area which has been swept away by its vast waters. We believe these great coal-fields once formed one unbroken coal-area, and may therefore be appropriately named, as a whole, the "Great Central coal-field," though we have named them respectively the "Central" and the "Western." But the time may come when the develop ments of the West will render the term " Western," as applied to the coal of Missouri and Iowa, a misnomer.