5 8 THE POPULAR SCIENCE MONTHLY. 



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 

 cai'boniferous flora, have not been able to reconcile the orderly ar- 

 rangement 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 sand- 

 stone 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 nat- 

 ural, 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-Etienne, 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 re- 

 markable 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 there- 

 fore in its immediate neighborhood. The coal-beds themselves were 



