APPALACHIAN FORMATIONS.
In the accompanying illustration, Fig. 4, we do not give the details of the foldings and steep reversed dips of the mountain-chains now filling the eastern edge of the ancient sea. Such detail would not affect the question, but would, in the limited space to which we are confined, complicate and confuse the general idea we wish to impress.
It will be noticed that on the left, or east, the granite rocks still form, on a lower line, the bounds of the basin; while in the background, on a higher line, is shown the ancient volcanic belt towering above the Alle ghany summit; while the streams of lava from its crest are poured into the great sea, forming, in the early periods and in the boiling waters, the crystalline gneiss, and during later eras, the higher sedimentary sand-rocks.
It will be proper to remark, here, that the line represented by the illus tration is a transverse section across the Appalachian chain by Cumberland, Maryland, and does not fairly present the deep flexures of the east or in the vicinity of the anthracite coal-fields, whose location are, however, denoted.
It is also necessary to remark that volcanic action was not confined entirely, though principally, to the surrounding granite zone. In all pro bability, active volcanoes existed in the interior of the basin, particularly before the formation of the great limestone,—the Auroral, or No. II., of Rogers,—as we have shown in several instances; but their location we can only tell by the anticlinals which now swell the surface. And these are not positive evidences, since the original surface of the granite floor was, in all probability, usually corrugated and uneven. Those minor details, however, do not affect the proposition regarding the origin and formation of the great basin, which we assume to be as generally set forth : that the ancient sea was deepest on the northeast, and bounded by a zone or belt of volcanic mountains, which produced the material, in part or in whole, now reposing in its deep gulfs.
As before stated, the granite shores were precipitous, and, consequently, weakest on the east or sea margin. Hence, volcanic action was confined to that side, and the mountain-barrier gradually worn down as the waters became shallow by the filling up of their depth. The enormous amount of material thrown into those deep basins would naturally raise even the waters of the sea, and as naturally cause not only the general depression of the crust of the earth in an eastern direction, but wear down the mountains themselves. The most natural consequence of this raising of the waters and depression of the land which confined them, was the final escape of the pent-up sea from its ancient limits, and the overflowing of the land to the east; and whether the Atlantic then existed on a level with the Appalachian Sea or not, the effect would be the same; for the granite hills of the east, worn on one side by the billows of the Atlantic, and on the other by the waves of the ancient sea, could not resist their abrading influences, while the fierce volcanic action still wore down the crater and still depressed the crust.
But a portion of the ancient barrier resisted the combined attacks, and still stands to attest the magnitude and grandeur of those ancient limits. We allude to the mountains of East Tennessee and the adjoining States. Yet it is singular that the thickest portions of the crust, or where we might assume the greatest magnitude of mountain border to have existed, towards the northeast, first yielded to the combined action of the fire and water. It is, however, only another fact to prove the general truth of the hypothesis, since the investigations of all our geologists show that the greatest amount of solid matter now filling the great basin came from a northeasterp direction; and 'bence the more rapid subsidence of the crust in that locality, since such be the natural sequence of the more rapid ejection of the fluid matter': porting the crust.