If we take an average forest of our present day as the base of our cal culations, we find that an acre of ground containing 65 trees, each ave raging 240 cubic feet of solid timber to the tree, or five tons, and containing 20 per cent. of carbon, will produce 65 tons of charcoal; or it would require 74 such forests to produce a bed of coal one foot thick, which con tains 4840 tons of coal. To pursue the subject further, we may assume such a forest of white oak to have been one hundred years in coming to perfection, and we thus find that it would require 7400 years of our present forest growth to form a bed of coal (3) three feet thick; or 74,000 years to accumulate the mass of coal existing in our 30-foot Mammoth coal-bed.
We may indulge in some speculation as to the relative time required to produce the same result during the ancient flora. We find the heat, the moisture, the carbon, and the water, all combining to produce an excessive growth; and we may safely assume that each year of such growth would add one foot to the thickness of the vegetable mass, as before described. This might be compressed, in the shape of coal, to one-fifth its bulk or weight, and all that it would lose in the slow combustion, or process of charring, in the bowels of the earth, would be more than supplied by the accession of carbon and hydrogen from the subterranean vapors still per vading the earth, air, and water. This would require five years to pro duce one foot of coal! or 180 years to form the 30-feet coal of the Mammoth.
We cannot conceive of any other natural process by which our large veins of coal could be formed direct from vegetable matter.
If we assume the vegetation to have been arborescent and the peculiar fossil flora of the land, we cannot possibly accumulate a sufficient mass, by any theory, to produce a three-foot vein of coal. Growing on the land, and, consequently, in the air, the growth of successive years could not have been preserved, and the growth that could have stood on the place where it grew, could not have formed one of our smallest available coal-beds.
If we assume the vegetation to have been of the peat, or bog, order, we must admit the whole of the vast area of our Appalachian coal formation to have been level, and the gradual subsidence of the land would then conform, in part, to the requirements of the facts sustaining the theory.
But even they sustain this theory of peat-bog formation require the growth of 1500 years to form the ten-foot Pittsburg seam.
We do not believe that Nature worked so slow. At this rate of pro gress it would require 15,000 years to form our 100 feet of anthracite coal, or perhaps ten times that period to deposit the 3000 feet of coal measures in which this coal is stratified; while the total thickness of the fossiliferous strata, from the azoic to the cainozoic; would require the lapse of millions of years. Such a state of progress is unnecessary, unnatural, and not
consistent with the facts.
We have no doubt that the mighty work of creation was accomplished in far less time than our present data would indicate; we cannot judge of the productions and processes of the past by the present.
Tracing the process of Nature in filling the great Appalachian basin with strata upon strata, we have no reason to think that numberless ages transpired during its accomplishment. The rivers of molten lava poured out by a hundred volcanoes would accumulate the mass in a comparatively short. space of time. It may be argued that such could not have been the real nature of the process, in view of the animal life that then existed. But it is evident that no other cause could effect the mighty change from an unfathomable ocean to a vast continent; and, therefore, such must have been the cause and effect to a greater or lesser degree. The low order of animal life then existing was only found in strata which indicate repose and quiet; they therefore sprung into existence during every short period of rest, and vanished with the return of violence and change, as the many paleontological breaks in the ancient strata indicate unequivocally.
Whether the theory of the water vegetation—which we may term "super aqueous," since it really grows above the water, while its roots are below it—or the peat-bog formation be accepted, or, in fact, any other, the same subsidence of the land and the same changes of condition are required to account for the intervening strata of slate and rock which form our coal measures. In the former, however, the subsidence of the land is not a positive necessity to account for the superincumbent strata, since the vege tation filling the water would be crushed down by accumulating earthy matter, and the sedimentary process and the formation of coal-beds might go on without the necessity of a gradual or an intermittent subsidence. The question is, whether or inot the tall vines of the Sigillaria, &c. could reach the surface from the vast depth of 3000 feet, or the total thickness of the coal measures. We do not think the proposition at all probable, since the evidences of a gradual subsidence of the interior basin, or per haps the entire Appalachian formation, is overwhelming and unequivocal.* We may consider for a moment the conditions and changes which re sulted from a subsidence of the land, or a depression of the vegetation forming a distinct coal-bed,—the process by which • the superincumbent strata formed, and the inauguration of a new growth of vegetation.