ANTHRACITE COAL FORMATIONS.
Of the fact that our anthracite coal-fields are part of the great Appa lachian coal formation there is no question ; and that they were formed at the same time, and under nearly the same circumstances, is not doubted ; but the cause which led to the subsequent change from bituminous to anthracite is a matter of some argument.
According to the topographical features of the present Alleghany coal field and the dip of its strata, the anthracite fields are not conformable, and we have reason to believe that this non-conformity existed, though to a less extent, prior to the formation of coal. Had the same angle of dip pre vailed which gives to the Alleghany field its basin shape, the elevation of the anthracite fields would have been considerably above the present eleva tion of the Alleghany Mountains. We have no doubt these fields were higher than they are now, but their immense deposits could only have been formed in corresponding basins, independent of the great or main basin ; they never grew into their present magnitude on its mere edges.
The anthracite coal was, therefore, formed in deep, isolated lakes, whether in two or three can scarcely be determined, but all the area covered at pre sent with conglomerate must have been under water at the commencement of the Carboniferous era, and probably much more that has since been denuded : therefore the presumption is they were originally of much greater extent than at present.
The folding of the strata in the vicinity of the anthracite coals—resulting, as before stated, from subsidence as a first cause, and lateral contraction as the last and second—naturally formed lakes or basins in this locality, as the same abrupt strata exist in the vicinity of the same line of volcanic vents, from one end of the coast range to the other.
Close proximity to the region of intense volcanic heat not only tended to keep the waters warm, but increased the vegetation and imparted to the elements great volumes of the vapors of carbon and its resulting gases, in connection with the hydrogen of water and the oxygen of the air.
We have noticed all our Paleozoic formations in the great Appalachian basins are decreasing from east to west, and that all our stratified rocks are much thicker on the Atlantic edge of the basin than in the interior. This law or condition also applies to the anthracite coal, which is nearly two thirds thicker than the bituminous coals of the interior, or farther west. The cause undoubtedly had its existence in the same source which produced the superior thickness of the strata, viz. volcanic action, increasing both the heat and the volume of carbon.
We may apply the same theory of coal formation here which has been applied to the bituminous beds farther west, and find the conditions and coincidents to be still more favorable.
The deep-rooted Sigillaria, the towering Lepidodendron, and the gigantic Calamite, with their numerous species, have filled the deep lake to its brim, and a magnificent luxuriance of foliage spreads over its surface ; carbonic acid shrouds the dark green in still deeper hues, and imparts to the growth a vigor unknown to later ages. Bitumen and carbon oils float through the mass, preserving it from decay and adding vast acquisitions to its bulk, until the face of the lake presents no appearance of water, but one vast sea of fronds and low leafy vegetation.
A shower of volcanic dust and ashes might crush the tender growth, and form a streak of slate or bone, and yet not sink the floating mass of vegetation. But ultimately its own weight would sink it to the bottom, and a new growth would arise, with but a slight interval, until even a "mammoth" of 60 feet thickness accumulated in its depths, with all the regularity of bench, and bone, and slate, or even parting sandstone.
Eventually these changes take place, as the result of subsidence or vol canic action, which stop the growth of the aqueous vegetation, and cover the mass hitherto formed with immense deposits of arenaceous and argilla ceous sediment, drift, or volcanic eruptions.