11. Rocks of diverse formations are also characterized by the nature of the fossils they enclose. The most ancient ones contain vegetable and animal remains, which have entirely disappeared from the surface of the globe. Certain more recent species have completely disappeared, but have preserved an analogy, which differs only in size and slightly in form. Others, of which we see the last representations, are tending evidently to disappearance in a near future, such as the elephant, rhinoceros, hippopotamus, etc. Thus, as the terrestrial beds approach our epoch, the animal and vegetable species they contain approach those animals and vegetables which still exist.
The perturbations and inundations which have taken place upon the Earth since its origin have completely changed the conditions of vitality, and have made entire generations of living beings disappear.