478 FOSSIL INVERTEBRATED ANIMALS. 



primitive limestone rocks, which are evidently anterior to all 

 species of organization, whether animal or vegetable, and the 

 existence of which we may suppose to have been contempora- 

 neous with the formation of the terrestrial globe itself, we 

 observe that the most ancient secondary calcareous strata 

 contain extremely few vestiges of calcareous bodies, whose 

 existence had scarcely commenced when these early strata 

 were formed. 



From this point, that is, from the transition strata, the num- 

 ber of marine bodies gradually increases, in an immense pro- 

 portion to the antiquity of the strata which contain them. We 

 have already noticed the diversity of species, which, on the 

 contrary, is in a direct proportion with the antiquity of the 

 strata. The older the strata, the more diiTerent the species 

 from any now existing ; and even where there is an approxi- 

 mation of form between them, there is generally an immense 

 superiority of size on the side of the fossils. 



It would appear that the first living beings which were 

 found in the ocean were some small shell-animals, — such, at 

 least, are the only animals which have left any certain traces 

 of their existence in the most ancient secondary strata. 



On the assumption that this globe was originally submersed 

 in water, we may suppose that when the surface of the ocean 

 was sufficiently lowered to permit the light to arrive at the 

 summit of the mountains, some zoophytes were formed there 

 with solid body and fixed habitation, and that these multiplied 

 progressively, as well as the shells, in proportion as the solar 

 rays could exercise their vivifying action on more extended 

 spaces in the bottom of the seas. 



After the retreat of the sea from above the continents of the 

 globe, and before the valleys were completely formed, the 

 rain waters must have collected in numbers of places, and 

 formed vast lakes, the depositions of which gave rise to those 

 strata, little remarked before our own times, and to which the 

 name of fresh-water formations has been given, because the 



