ANTHRACITE COAL.
We have before stated that vegetable matter may, and in all probability did, aid in producing coal, but, we believe, only to a very limited extent. That vegetation grew luxuriantly during the coal era there can be no doubt; and that it grew in the deep basins in which coal was formed is likewise evident; but that the woody fibre of vege tation formed coal is not only doubtful, but contrary to all evidence, and at variance with the coincidents of coal formations. It may have formed the impurities—bone and slate—of the coal, but never its pure carbon. The woody tissue supposed to be detected by microscopic examination cannot be determined in pure coal; and that found, or sup posed to be found, in the ashes of coal is no criterion, since if the woody fibre of plants formed any part of a coal-seam it must have been the earthy parts thereof.
We have rarely seen a fossil plant in the midst of a coal-bed or within the coal; but whenever found in this condition it is not coal, but slate or bone.
A specimen may be seen in the office of Messrs. Connor A Patterson, of Pottsville, Pennsylvania, which demonstrates this fact. Coal-plants of the Carboniferous.era, in a fossil condition, are invariably silicious or calcareous, and partake of the Ethological character of the formation in which they are found.
But we do not intend to deny that the magnificent flora of the Carboniferous era aided in the production of coal. We believe it did, and have before so stated. That the rich and resinous calamites, coniferie, &c., which were fed by a superabundance of carbon and carbonic acid, should yield oil on pressure, there cannot be a doubt; and that they were subject to immense pressure between the rocky strata in which they now exist is evident not only by their flattened forms, but the fact that the superincumbent strata would exert such an influence and expel the resinous oils which they contained. This
oil would mingle with the hydro-carbons, and, by evaporation, form bitumen; and this, enclosed in the strata of the coal-measures and subject to pressure, would produce coal.
We gave the best vegetable theory available in the early pages of this book, but stated then that we did not consider any of those theories tenable. We are now positive of the fact, and state positively that all pure coal-beds are formed from petroleum or oil, resulting from the vapors of carbon directly or indirectly, as above set forth.
That a gradual depression of our great coal-basins did take place is not only evident from existing facts, but the natural processes of condensation and contraction. It is not, however, necessary that such must have been a condition to account for the forma tion of our coal-beds and the accumulation of the accompanying measures, since these beds and the rocky strata in which they exist would form as regularly and uniformly in basins of a constant depth as in those of varying depths.
The fact, in this case, that coal-beds are invariably thin at a great depth, or more so than they are at moderate depth, is explained by the simple fact that they must have existed originally in a soft and plastic condition, and were, consequently, moved by the great pressure of water and sediment resting on them from the centre of deep basins towards their edges,—a fact demonstrated in all deep basins, except that of Richmond, Virginia, where the irregular form of the intermediate basins prevented such a move ment.