THE NEOZOIC AGES. 245 



or shortly succeeding these, were species representing 

 the Eodents, or gnawing animals, and many other 

 creatures of the group Pachydermata, allied to the 

 Modern Tapirs and Hogs, as well as several additional 

 carnivorous quadrupeds. Thus at the very beginning 

 of the Tertiary period we enter on the age of mammals. 

 It may be well, however, to take these animals some- 

 what in chronological order. 



If the old Egyptian, by quarrying the nummulite 

 limestone, bore unconscious testimony to the recent 

 origin of man (whose remains are wholly absent from 

 the Tertiary deposits), so did the ancient Britons and 

 Gauls, when they laid the first rude foundations of 

 future capitals on the banks of the Thames and of 

 the Seine. Both cities lie in basins of Eocene Tertiary, 

 occupying hollows in the chalk. Under London there 

 is principally a thick bed of clay, the ^' London clay,'^ 

 attaining a thickness of five hundred feet. This bed 

 is obviously marine, containing numerous species of 

 sea shells ; but it must have been deposited near land, 

 as it also holds many fossil fruits and other remains of 

 plants to which we shall refer in the sequel, and the 

 bones of several species of large animals. Among 

 these the old reptiles of the Mesozoic are repre- 

 sented by the vertebrae of a supposed ^^sea snake'' 

 (Palseophis) thirteen feet long, and species of crocodile 

 allied both to the alligators and the gavials. But be- 

 sides these there are bones of several animals allied 

 to the hog and tapir, and also a species of opossum. 

 These remains must be drift carcases from neighbour- 



