It will scarcely be necessary to state that the limits of the ancient sea were at this period largely contracted. The enormous mass of material which filled up the eastern edge of the basin, being vastly in excess of that carried by the waters towards the interior, naturally elevated the eastern shores and drove the waters back, thus forming a long line of new shore, parallel with the old granite range, and of great width,—extending, for instance, in Southwestern Virginia, over a distance of 150 miles, or from the granite hills of North Carolina to the eastern escarpment of the Alle ghany in Western Virginia. This was general along the eastern edge of the basin, though much narrower at some points than others; the anthra cite fields of Pennsylvania being the most eastern, and, of course, nearest to the original granite boundary of the ancient sea. But even here the new line of shore could not have been less than 50 miles from the Sharp Mountain to an indefinite point south of the Blue Ridge or Reading Hills.
The sea was driven back by the constantly encroaching land, the pro duction of volcanic action. But in order to explain its elevation as dry land along the newly erected coasts, we must assume the depression of the interior and the gradual subsidence of the waters. This, however, is not a mere inference. Prof. Rogers demonstrates this clearly in his theory of the origin of coal ; and so many evidences are offered of the fact, that we state it as such.
We now find, instead of the vast Appalachian ocean, an inland basin of comparatively contracted limits, with rivers draining the new continent, as the New River now drains that portion which preserved its original physical features. The St. Lawrence, the Hudson, the Delaware, the Sus quehanna, the Potomac, and the James did not then pass their waters towards the Atlantic, but flowed in unknown courses towards the great inland sea. The St. Lawrence brought down the accumulated waters of the north, with their vast debris, along the eastern coast. The ancient Missouri then, as now, rolled its muddy waters to the south.
It will not, under such circumstances as these, appear strange or wonder ful that the great Appalachian Sea no more exists ; but it would be strange if those accumulating waters, rolling down over soft and imperfectly formed strata, did not fill up the shallow sea.
The physical changes in the drainage and topography of the eastern edge of the Appalachian strata are due to subsequent events. The anthracite basins were part and parcel of the great Appalachian coal-field, and formed in the same manner and at the same time with the bituminous coals of the West.* The intervening space might not have been occupied by a continuous coal-field ; but we have existing evidences, in the many outlying patches of coal and conglomerate, to prove that the larger portion of the now denuded area was at one time occupied by coal formations ; and the fact of their denudation by eastern waters is a positive evidence of the change in topography after the formation of our coal-fields. Conse
quently, the waters must have flowed to the west until this period.
We noticed the causes of this physical change in the commencement of this chapter ; but it may appear plainer in this than in that connection. The gradual subsidence of the earth's crust was general at the period of which we write,—or during the coal era,--at the close of a season of con stant and violent volcanic action, and enables us to account for our coal formations, we think, in a plain and practical manner, which could not be done under any other hypothesis.
But the rapid subsidence or greater depression in the eastern synclinals, or valleys, requires some definite explanation. As we before stated, a long line of granite shore runs parallel with the ancient Appalachian sea, and with the present range of Appalachian mountains ; and the probability is that not only one but several ranges of the same kind originally existed along the bottom of the ancient sea, corresponding to our present flexures or mountainous folds ; since the early dynamic effects of internal forces seem to have been in long parallel lines,—a fact attested by the physical features of the earth, which always exist in long lines of mountain and valley, except when changed and distorted by central volcanic influences.* This form of topographical structure being demonstrated,—as, we think, all the facts hitherto given do fairly demonstrate,—we may next allude to the fact that the eastern portions of the ancient sea must have been vastly deeper than the interior, as before stated and proved. These facts being accepted, we are now prepared to offer a plain solution of the problem of inverted strata, and the deep synclinals of our eastern basins.
In the first place, these deep axis of formation must have been originally the weakest part of the earth's crust; in the next, they were in close proximity to the active volcanoes of the plutonic regions of the coast, and the spasmodic venting of incessant streams of lava, which filled the vast extent of the Appalachian Sea, must have tended to cause a vacuum in the bowels of the earth; and, as "nature abhors a vacuum," nothing can be more natural than the subsidence of those deeper basins, in the vicinity of this constraining cause.* The inverted strata or flexures of the Alpine formations have the same form and feature, and were evidently caused by the same volcanic action. But this cause could only operate during the continued action of volcanic influences; and there has evidently been a continued subsidence of those deep basins since the formation of our coal-fields, which needs further explanation.