FORMATION OF THE APPALACHIAN OILS.
We have shown that the vapors of carbon produce oil direct from volcanic sources and the internal heat of smouldering subterranean fires. This seems too palpable a fact to need more explanation or illustration; and, since we can see and comprehend in this a natural and probable process, it is neither profitable nor necessary to seek other theories which offer no means of demonstration. Most writers on this subject ascribe the production of rock-oil to the organic remains which lie entombed so thickly in the Devonian formations. But we think there is little probability that all the millions of mollusca entombed beneath the rocky crust of Venango would produce the flow of a single great well like the Noble, the Sherman, or the Phillips: a "shoal of whales" would not produce such astonishing results. That the fat of these ancient inhabitants of the inland sea should accumulate in certain localities to produce our present reservoirs of oil is likewise not only improbable, but impossible. Liberated oil or gas always rises to the surface of water, and this ancient life could only exist in water, and only find their tomb beneath it, from whence their oil must ascend to the surface almost im mediately, as the results of pressure and heat. It, therefore, could never again sink, or exist beneath the water in the shape of oil or gas, but only as coal or bituminous shale.
But there are other reasons, more conclusive, against the theory of the formation of oil from the organic remains entombed in the Devonian oil-bearing rocks. Every cir cumstance of the formation and existence of the strata filling the Great Basin demon strates the fact of heat and volcanic violence as the general accompaniment of every great sandstone formation, and the paleontological breaks following these extensive formations likewise demonstrate the fact by the destruction of life during these periods. It is evident, therefore, that the ancient life was entombed during periods of great heat, and that its oils were expelled both by the temperature of the rocks and the water, and by the pressure of the rocky strata in which they were buried. The oil thus expelled would then rise to the surface of the water, and no process could afterwards seal this oil in the earth except in the form of coal or bitumen. Never, since the periods of time during which those great changes occurred, have the conditions been so favorable for the production of the oils from the organic remains or fossils of the Devonian rocks, and these fossils, if now subject to test, produce less oil than the rocks above them. We, therefore, cannot accept this theory as a probable or a possible one to account for the existence and formation of petroleum.
As stated and demonstrated, the existence and production of petroleum were in far greater abundance during the Carboniferous era than before or since: before, because the heat was too intense to admit of its condensation from vapor and gas; and since, because the temperature of the earth has been too low to produce the vapor or gas in abundance. The Carboniferous era witnessed the waters of the Great Basin covered
with the bituminous results of petroleum, like the pitch lakes of Trinidad and Texas, and the beds of coal were precipitated by their own weight or the rapid accumulations of the rocky strata over them during the seasons of volcanic action, which were then intermittent.
The lower coal-beds in the proto-Carboniferous strata are limited, and even the first beds in the true coal measures and on the conglomerate, or millstone grit, are compara tively small, impure, and thin; but the succeeding beds are in some localities immense, as witness the great Mammoth bed of the anthracite regions and the middle beds of the Alleghany coal-field generally. But we again witness a depreciation in the upper measures, and the last beds formed are thin, few, and valueless, because the tempera ture at this period was much lower, and the production of petroleum, consequently, much less abundant.
It is natural, however, to assume that the gases which produced the petroleum on the surface of the water should accumulate still at a greater depth after the completion of the Palceozoic column, since the heat receded from the surface, and the rocks at a great depth still maintained a comparatively high temperature. The gases thus accumulating were then sealed in the rocks beneath the coal by the closing of the pores of the earth by contraction and condensation.
That this process continued for a considerable period after the formation of our great coal-beds is manifest, from the fact that the Devonian rocks are impregnated with bitumen, which could not have resulted prior to the formation of coal, because the gas up to the period was too light to be condensed by the heated rocks: indeed, they rather tended to keep the gas in its volatile condition, and could not have taken up the bitumen of the condensed gas, forming oil, until a late period.
This fact is further demonstrated by the absence of bitumen in the Eastern forma tions and its abundant presence in the formations of the West. In the East, the tem perature was much higher during• the formation of the massive sandstones which here predominate, than it was in the West, where the limestones accumulated during the same periods. Here we find but little bitumen in the rocky strata, but there we find bitumen general in all the strata, and some of the rocks saturated with it, as the Cor niferous limestone, for instance. Here we find the bitumen resulting from the super abundant vapors and the subsequent petroleum in massive and solid beds of anthracite; there we find it in a few thin beds of highly bituminous coal, proving that the tempera ture was lower in the West than in the East, and that, while the petroleum produced was originally more limited, it combined with the rocky strata, in which it condensed, instead of arising to the surface of the water to form large beds of coal.