THE WORLD BEFORE MAN 21 



existed, and their places in nature were occupied by 

 lower types. 



Nor for similar reasons would we expect to meet 

 with man in the earlier part of that last, or ceno- 

 zoic, period in which we still live ; and in point 

 of fact it is only in superficial deposits of the later 

 part of this last great period of the earth's history 

 that we actually meet with evidence of the existence 

 of the human species. 



If there is based on this fact a question as to the 

 actual date of man's first appearance, the physical 

 considerations indicate about twenty millions of years 

 for the whole duration of the earth. Setting apart, say, 

 a fourth of this time for the early pre-geologic con- 

 dition of the world, the remainder may be roughly 

 estimated as five millions for the archaean, or eozoic, 

 six for the palaeozoic, three for the mesozoic, and one 

 for the cenozoic. 1 Of the last, the later part, in 

 which there is a possibility of the existence of man, 

 will be limited to less than a quarter of a million ; 

 and within this the certainly known remains of man, 

 whether attributed as by some to the latest inter- 

 glacial period, or to the post-glacial a mere question 

 of terms, and not of facts cannot be older, according 

 to the best geological estimates, than from seven 

 thousand to ten thousand years. This, according to 

 our present knowledge, is the maximum date of the 



1 The absolute length of these periods is, of course, a matter of 

 estimation ; but the relative lengths of the different ages may be re- 

 garded as a fair approximation, based on facts. 



