THE WORLD BEFORE MAN 23 



ancestor of man, by the occurrence of connecting 

 forms, or otherwise. As the facts now stand, the 

 earliest known remains of man are still human, and 

 tell us nothing as to previous stages of development. 

 We must now glance a little more particularly at 

 what may be termed the more immediate antece- 

 dents of man. The latest great period of the earth's 

 geological history (the cenozoic) was ingeniously 

 subdivided by Lyell, on the ground of the percentages 

 of extinct and surviving species of marine shells con- 

 tained in its several beds. According to this me'thod, 

 which, with some modifications in detail, is still 

 accepted, the eocene age, or that of the dawn of the 

 recent, includes those formations in which the per- 

 centage of modern or still living species of marine 

 animals does not exceed three and a half, all the other 

 species found being extinct. The miocene (less re- 

 cent) includes beds in which the percentage of living 

 species does not exceed thirty-five. The pliocene 

 (more recent) includes beds in which the living forms 

 of marine life exceed thirty-five per cent, but there 

 is still a considerable proportion of extinct species. 

 Newer than this we have the pleistocene (most recent), 

 in which there are scarcely as many extinct species 

 as there are of recent in the eocene. Lastly, the 

 modern, of course, includes only the living species of 

 the modern seas. Other geologists, notably Dawkins 

 and Gandry, have arrived at similar results from a 

 consideration of the vertebrate animals of the land. 

 In the eocene we find numerous remains of mammals, 



