Page:Popular Science Monthly Volume 23.djvu/68

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phere saturated with moisture was therefore essential to their vigor; and in such an atmosphere, according to M. Grand' Eury, they grew continually, without interruption by changes of season, without rest or alternations, to exhaustion; then to fall to the ground, and give place to other similar growths. So luxuriant a vegetation could only have been produced by the combination of an ultra-tropical heat with an excessive humidity, under no other changes of seasons than those distinguished by intervals of relative calm and of torrential rains. At the same time, the superabundance of green parts, which characterized even the trunks of the trees, presupposes a considerable intensity of light; and all the phenomena point to a strong diffused light, the direct rays of the sun being tempered by the interposed veil of vapors, as that under the influence of which these growths were produced.

The third element of the problem, that of the material disposition of the places in which the coal was formed, is the one that has offered the most difficulties. Two theories have been held on this subject. One is, that the materials were carried by ocean-currents or rivers from considerable distances to the places of deposit. Naturalists, however, who have applied themselves specially to the study of the carboniferous flora, have not been able to reconcile the orderly arrangement of the fragments, in which the specimens are so delicately posed, mingled without confusion, and often distributed uniformly in collections of leaves of the same species, with the confused drifts which are the almost invariable results of such a method of transportation. Moreover, in all coal-regions, recognizable trunks of calamites, tree ferns, sigillarias, and other types of the carboniferous flora are found in the neighborhood of the coal, vertically crossing the strata of sandstone that accompany and separate the coal-beds in such a manner as to show that they grew over the ground of the whole region, and to indicate that their transformation was dependent upon some special or local phenomenon which may have been quite simple, or at least natural, and were probably resultant from the physical conditions of the land at that epoch. The other theory, that coal originated in the decomposition of trees and plants that grew on the spot, is insufficient to account for all the phenomena and circumstances, and raises new difficulties.

M. Grand' Eury, in whose theory transportation, but of a different character from that presumed in the first of these two theories, forms an important element, has been enabled, through his investigations at Saint-√Čtienne, to form a clear idea of the nature of coal and the processes to which we owe it, and also to enter into the details of the matter, to go back to the true causes of the processes, and to describe with remarkable precision how they must have taken place. The land of the carboniferous formations appears, after an intelligent examination of the stratigraphy, to have been frequently covered by the sea, and therefore in its immediate neighborhood. The coal-beds themselves were