NATURAL PROCESSES.
Volcanic ranges generally exist in long lines along the weaker axes of the earth's crust, and where these volcanic vents exist, there those weak lines naturally remain ; where the condensed vapors and lava of the earth first find vent, there it will continue to vent; because, while other portions of the crust are growing thicker and stronger in consequence, these points remain much the same. They always exist in granite forma tions, though frequently overlapped by the metamorphic, and sometimes nearly covered by the Palaeozoic.
The great ranges of volcanoes, extinct or otherwise, which now extend over the face of the earth, existed in the early days of creation as soon, or almost as soon, as its granite crust was formed; for, as soon as condensation and consequent contraction took place, the confined vapors and molten matter began to exist in a state of tension, and forced their way through the accumulating crust, when that tension became too great, in long and immense lines of volcanic vents.
Mountains also assumed lines rather than cones, following almost invariably the vol canic lines, and resulting from lateral contractions, which naturally formed its folds on the weakest points, as represented in figure 6, Chapter III. The great volcanic lines formed the harriers of great basins or seas, since they occupied the highest points and the water the lowest. But up to the period of the metamorphic or crystalline stratified rocks the earth was surrounded by vapors, and the oxygen and hydrogen only combined to form water when the temperature admitted of its existence in that condition, instead of in the state of steam or vapor.
The metamorphic rocks were formed by the lava vented from the volcanic ranges into the water surrounding them, which, being hot, crystallized the lava deposited as sedi ment. On being thrown into the water in a molten condition, the lava was shivered to atoms, and thrown up into the air with steam and vapor, to be carried by winds and tides and waves, as ashes and dust, to remote localities.
This process must be rapid. A long line of active volcanoes, reaching perhaps from Nova Scotia to Cuba, vented, almost without intermission, immense streams of lava into the deep waters of ancient seas forming the Great Basin. Such a process would not require millions of years to form our metamorphic strata : perhaps a few years might suffice.
That such a line of volcanic vents did exist along our Eastern granite range, there is ample evidence to prove; and that such was the process by which not only our meta morphic but our great Palmozoic sandrocks were formed, admits of palpable demon stration.
We find the basins deepest along this line of vents, proving the depression to have been greatest here; we find the strata at very high angles of inclination, sometimes inverted, in evidence of the lateral contraction, which naturally produced its apparent results along the weakest lines of the crust; we see a vast difference in the thickness of the strata hero than elsewhere, and we notice that it gradually grows thin and fine grained as it recedes from the place of production. It is plain that the immense plates of sandstones, shales, slates, iron ores, and coal could not be produced by rivers, tides, waves, or other causes, from the wear and tear of higher lands surrounding the Great Basin, since each of those immense horizons is the product of one cause, one operation, one period, and is formed of the same material throughout. Had they been produced by other causes than volcanic action, they would have presented a breccia,—an olla podrida of divers material.
But the great horizons formed by the Potsdam sandstone, the Medina or Levant, the Vespertine, and other rocks are coextensive with the great Palmozoic basin between the Blue Ridge and the Rocky Mountains. They are invariably thin towards the West— mere knife-edges; but along their Eastern outcrops they are of immense thickness. And not only do the sandstones present this evidence of their source, but all the accompanying strata present, by their decreasing thickness and coarseness, evidence of volcanic production from the Eastern line of vents.
The vapors of carbon arising from this great region of heat must have been in greater volumes than anywhere else within the Great Basin. But the intensity of the heat pre vented their condensation, or the formation of oil, until a comparatively late era, along this range ; when the temperature permitted it, we find the results in our immense beds of anthracite coal; but we do not find the rocks impregnated, because its conden sation did not take place while ascending through the rocky strata, but through the waters of our deep coal-basins, on the surface of which it floated and gave up its more volatile hydrogen, leaving a resulting bitumen almost, and in some cases entirely, de void of hydrogen, oxygen, or other gases, and a pure carbon in the shape of anthracite coal. It would be almost impossible, during a time like this, or, in fact, at any time, for a deposit of this kind to form on the surface of the water without the addition of earthy impurities from floating dust, ashes, and smoke to some extent.