Species of the Secondary and Tertiary Formations ? 253 



ters which do not really belong to them. May we not sup- 

 pose that, if we were acquainted with the numerous modifi- 

 cations of the domestic races only from parts of their skele- 

 ton, which had been left in the strata of the earth as fossils, 

 we would form many distinct species out of one and the same 

 race \ The characters which led us to separate them, would 

 acquire in our eyes an importance as great as those which 

 now serve to distinguish the ancient generations from the 

 existing creations. 



There exists, therefore, at least uncertainty in the deter- 

 mination of a great number of fossil species, when we con- 

 sider them as distinct, when we regard them as having no 

 representatives in nature, and finally when we assimilate 

 them to the races of our own epoch. It is more especially 

 in making these approximations that we run most risk of de- 

 ceiving ourselves ; for here all control is impossible. On the 

 other hand, a multitude of characters are wanting to enable 

 us to judge of the identity of races which have belonged to 

 periods so different in the whole of their conditions and their 

 exterior media. 



This identity, whether it be real or not, cannot well be dis- 

 cerned, except in regard to geological eras most nearly ap- 

 proaching the period to which we belong.* In fact, it is only 

 in the most recent tertiary strata that species have been ob- 

 served, which present analogies to our own, sufficiently strik- 

 ing to admit of identifying them . These affinities between the 

 old and presently existing generations do not, therefore, ex- 

 ist, but in regard to such races as have been subjected to the 

 same effects, and experienced nearly similar influences. 



The destruction of the species of the ancient world, seems 

 therefore to have been produced by a change of the exterior 

 circumstances in the media in which they lived. When these 

 changes in the conditions of the media have been consider- 



* It was supposed that species of our own epoch, such as Afurex trunculw and 

 Ostrcea hippopus, had been met with in the tertiary formations of Belnay, near 

 Tournus (Saone and Loire) ; but M. Virlet, who has examined these places, is 

 convinced that these shells, the animals of which had been used as food, had 

 been buried there by the hand of man. All idea of the marvellous is thus 

 banislted. (See Archive*, 1846, t. i., p. 338.) 



