Ch. III.] 



AND TERTIARY STRATA. 25 



of the subjacent rocks, whatever they may have been, which 

 constituted the original bed of the ocean. Now the degrada- 

 tion of these lands would commence immediately upon their 

 emergence, the waves of the sea undermining the cliffs, and 

 torrents flowing from the surface, so that new strata would 

 begin to form in different places ; and in proportion as the 

 lands increased, these deposits would augment. 



At length by the continued rising and sinking of different 

 parts of the bed of the ocean, a number of distinct basins 

 would be formed, wherein different kinds of sediment, each 

 distinguished by some local character, might accumulate. 

 Some of the groups of isles that had first risen would, in 

 the course of ages, become the central mountain ranges of con- 

 tinents, and different lofty chains might thus be characterized 

 by similar rocks of contemporaneous origin, the component 

 strata having originated under analogous circumstances in the 

 ocean before described. 



Finally, when large tracts of land existed, there would be a 

 variety of disconnected gulfs, inland seas, and lakes, each re- 

 ceiving the drainage of distinct hydrographical basins, and 

 becoming the receptacles of strata distinguished by marked 

 peculiarities of mineral composition. The organic remains 

 would also be more varied, for in one locality freshwater species 

 would be imbedded, as in deposits now forming in the lakes of 

 Switzerland and the north of Italy; in another, marine species, 

 as in the Aral and Caspian ; in a third region, gulfs of brackish 

 water would be converted into land, like those of Bothnia and 

 Finland in the Baltic ; in a fourth, there might be great fluvi- 

 atile and marine formations along the borders of a chain of 

 inland seas, like the deltas now growing at the mouths of the 

 Don, Danube, Nile, Po, and Rhone, along the shores of the 

 Azof, Euxine, and Mediterranean. These deposits would 

 each partake more or less of the peculiar mineral character of 

 adjoining lands, the degradation of which would supply sedi- 

 ment to the different rivers. 



Now if such be, in a great measure, the distinction between 



