51 
has been most extensively developed, but at present our information 
respecting this part of the world, from the want of good palontolo- 
gical specimens, is comparatively limited. 
Thus it is seen that the same types of mammals, of shells, and 
vegetable productions characterize the Eocene period in all parts of 
the world; although in some localities there may be a difference in 
specific or even generic characters. In the strata of this period we 
find the remains of extinct Crocodiles, but not those of any of the 
numerous Saurians which are met with in the older formations ; 
neither can we produce a single example of an Eocene Saurian or 
mammalian species existing at the present day. It is true, that the 
remains of the same genera of reptiles which now inhabit warm 
countries are discovered with the Mammalia of this period, and a 
few of the Eocene genera of Mammalia now exist; but the Tapir, 
Rhinoceros and Hippopotamus are respectively the nearest approx- 
imations to the Lophiodon, Paleotherium, and Anthracotherium of 
the Eocene catalogue. In the Cretaceous «ra some few fossils may 
approach the Eocene; and nothing is more probable than that crea- 
tures of a deep sea should have co-existed with those of a shallow 
sea or of an estuary. Some Infusoria and Polythalamia, according to 
Professor Ehrenberg, are specifically the same, and certain existing 
fishes are also generically identical with those of the Eocene deposits ; 
but in this country the separation between the Cretaceous and Tertiary 
formations is so apparent, that in our present state of geological know- 
ledge, no divisions can be followed with greater safety than those pro- 
posed by Mr. Lyell. 
In England the comparative anatomist has few opportunities of 
studying the remains of the early Tertiary animals. Binstead and 
Seafield in the Isle of Wight have afforded the best examples, and a few 
specimens have been obtained from other places*. Two teeth of the 
* Owen’s British Fossil Mammalia, pp. 299-806. 
H 2 
