216 MODERN AND ANCIENT COAL-FIELDS. [CHAP. XV. 



it overlies it, has deprived the upper coal of its volatile ingre 

 dients, while its influence has not always extended to lower 

 seams. In some spots, the conversion of coal into coke seems 

 to have been brought about, not so much by the heating agency 

 of the intrusive basalt, as by its mechanical effect in breaking up 

 and destroying the integrity of the beds, and rendering them 

 permeable to water, thereby facilitating the escape of the gases 

 of decomposing coal. 



In conclusion, I may observe that I was much struck with 

 the general similarity of this more modern or Oolitic coal-field, 

 and those of ancient or Paleozoic date in England and in Europe 

 generally. I was especially reminded of the carboniferous rocks 

 near St. Etienne, in France, which I visited in 1843, These 

 also rest on granite, and consist of coarse grits and sandstone 

 derived from the detritus of granite. In both coal-fields, the 

 French and the Virginian, upright Calamites abound ; fossil 

 plants are met with in both, almost to the exclusion of other 

 organic remains, shells especially being absent. The character 

 of the coal is similar, but in the richness and thickness of the 

 seams the Virginian formation is pre-eminent. When we behold 

 phenomena so identical, repeated at times so remote in the earth s 

 history, and at periods when such very distinct forms of vegeta 

 tion flourished, we may derive from the fact a useful caution, in 

 regard to certain popular generalizations respecting a peculiar 

 state of the globe during the remoter of the two epochs alluded 

 to. Some geologists, for example, have supposed an atmosphere 

 densely charged with carbonic acid to be necessary to explain 

 the origin of coal an atmosphere so unlike the present, as to be 

 unfit for the existence of air-breathing, vertebrate animals ; but 

 this theory they will hardly be prepared to extend to so modern 

 an era as the Oolitic or Triassic.^ 



During my visit to one of the coal-pits, an English overseer, 

 who was superintending the works, told me that within his 

 memory there had been a great improvement in the treatment 



* See a paper on this coal-field, by the author, Quarterly Journal Geolog. 

 Soc., August, 1847, vol. iii. p. 261, and an accompanying memoir, descrip 

 tive of the fossil plants, by Charles J. F. Bunbury, For. S. G. S. 



