THE ANCIENT APPALACHIAN SEA.
The margin of this ancient sea is not only now plainly defined to the eye of the geologist, but an investigation of the fact would lead to the same result.
In the first place, we do not merely infer, but we know, that originally the highest portions of the earth were mountains of the plutonic rocks, granite, &c., and that the boundaries of the ancient seas must have been those walls of granite,—since the gneiss, or first sedimentary rocks, could not exist until those mountain-barriers were erected to confine the ancient waters, in which only the crystalline or stratified gneiss could be formed. It is thus evident that the great zone of granite and gneiss which extends from Newfoundland, or Nova Scotia, in the northeast, to the end of the great Appalachian chain in Georgia, or perhaps to Cuba and beyond; and from the same point, north of the St. Lawrence and the great lakes, must have been the northeastern and southeastern boundary of the ancient sea. That this great zone or belt of granite was originally an elevated mountain-range, cannot be doubted, since it is positive that the waters which it confined were once as high as the tops of the Alleghanies. We are not left, however, to bare statements of this fact, since part of this great and ancient mountain-range still exists, with, perhaps, much of its olden grandeur.
We may merely mention the granite hills of New Hampshire and Maine, before we offer in evidence the vast and stupendous granite moun tains which pile up, in successive ranges, along the eastern margin of the Appalachian basin, in Southwestern Virginia, Northwestern North Caro lina, East Tennessee, and North Georgia. Here, where the denuding agencies of the escaping waters had no effect, the eastern barriers of the ancient sea still exist; and, had not the destructive effects of fire and water operated more violently in the northeast than the southeast, we should still find those impassable mountains barring our way to the West and cutting us off from the coal of the inland valleys: in fact, we should have mountains where we now have plains, and barren hills of granite where our cities now stand.
In order to strengthen the evidence still more, we may cite the fact that along this entire line or belt of granite unmistakable evidence is found of its early volcanic nature. Deep dykes, as the last effects of expiring volca noes, are found from Nova Scotia to Georgia,—generally along the eastern margin of the gneiss, but frequently through it.
The facts here stated must be borne in mind, to properly appreciate the facts which are to follow. Having given the bounds of the ancient sea,
we may now state its depth; and here we are not left to mere conjecture, for the thickness of the Palaeozoic strata which now fill its bed is evidently the measure of its depth.
The sum of their thickness has been measured pretty accurately by the geologists of the State. It ranges in the east from 25,000 to 35,000 feet, or from 5 to 7 miles, in thickness ! Now, when we consider that the formations are only part of the sedimentary rocks, which fill the deep caves of the ancient sea, that the metamorphic or crystalline sedi mentary strata still underlies, perhaps to the depth of 10,000 feet, or two miles more, and that the present elevation of the remaining portions of the ancient mountain-barrier in Virginia and Pennsylvania is elevated at least five thousand (5000) feet above the sea,—a base-line we have adopted,— we can form some conception of the enormous depth of the great sea to the east. This computation would give a depth of ten miles. But there are modifications of this estimate, such as the subsequent depression of the strata, which perhaps may have reduced the depth to two-thirds or one half the above vertical line. Yet the fact of an enormous depth still exists, even in five miles of water From the fact of depth, which cannot be doubted, we must assume another fact, which is no less self-evident,----which is, that the mountain barrier, or line of granite, bounding this deep sea, must have had one deep, perpendicular, or weak side, adjoining the waters on the west; while that on the Atlantic, or east side, must have existed to some extent in its pre sent gradually inclining form, since there is no evidence of change. The granite still exists, though greatly depressed.
We see now before us a long line of high and steep granite shores, and a deep, unfathomable sea ; and we have the existing evidences that these mountains were actively volcanic even until a late day, when the ancient sea no longer existed. The consequence has been that both the ancient mountains and the sea have disappeared ; the mountains displaced the sea, but the sea swallowed the mountains.
Here we may introduce an illustration of the rocks which fill the basin, and the natural causes which led to this result. It will aid in exemplifying the hypothesis we set forth, and which we hope to prove more by facts than by mere scientific conclusions, which hitherto have been our rule in fathoming what seems a natural phenomenon.