during the Formation of the Crust of the Earth. 83 



the most widely different of all from those of existing nature. 

 Some of them differed from the latter so much as to form sub- 

 classes or orders, — most of them at least gencrically. But in 

 proportion as, in the history of the earth, we approach the pre- 

 sent epoch, we observe a constantly increasing concordance of 

 the genera, or even, in certain cases, an identity of species with 

 our existing nature. 



7. In all times there have existed faunas and floras topogra- 

 phically distinct, in consequence of differences of conditions in 

 the stations, by reason of the distribution of the seas and the 

 elevation of mountains. But in proportion as the evolution of 

 the surface of the earth multiplied and varied the conditions of 

 stations, in proportion as seas were divided, continents extended, 

 chains of mountains elongated, and summits elevated, we also 

 see a diversification of the organized types and of their mode 

 of grouping and association. Topographical faunas and floras 

 became more clearly defined; and in all cases the number of 

 species living together constantly became more considerable. 



8. Amongst stations of remarkable nature, we must above all 

 indicate the immense marshes of Stigmaria in the carboniferous 

 epoch. Thanks to their long and numerous horizontal roots, 

 extended at the surface of the water, the Stigmaria appear in 

 course of time to have furnished a multitude of other plants with 

 the soil necessary for their development. The latter on perishing 

 became buried in the marsh, and there, protected from the access 

 of air, became gradually converted into coal, only permitting a 

 small number of fragments to decompose and become rotten at 

 the surface. It is thus that the accumulation of carbonized 

 substances could take place in a comparatively rapid manner 

 (nearly as in our peat-bogs), and the formation of very large 

 strata of coal consequently required a time perhaps less con- 

 siderable than is usually supposed. The alternations, repeated 

 hundreds of times, of strata of coal and sandstones or argil- 

 laceous shales, teach us that at that time a slow and gradual 

 sinking of the soil was taking place, during which the strata of 

 vegetable matter which had just been formed were covered 

 with mud and sand ; then the soil rose again. These continual 

 sinkings indicate the existence at this period of plutonic* move- 

 ments of the crust of the earth, in consequence of which, abun- 

 dant emissions of carbonic acid might take place during a long 

 period, as we see at present in certain countries. 



* It is, however, to be remarked, that such movements of the soil do 

 not necessarily involve plutonic action. The works of MM. BischofF, 

 Volger, and others appear to show, on the contrary, that sinkings of this 

 nature must, in most cases, have a cause entirely Neptunian. — E. Cla- 

 parede. 



6* 



