IN THE LAST HALF-CENTTJEY. 97 



elapsed since the earth was habitable by 

 living beings. If the conclusions thus 

 reached should stand the test of further 

 investigation, they will undoubtedly be 

 very valuable. But, whether true or 

 false, they can have no influence upon 

 the doctrine of evolution in its applica- 

 tion to living organisms. The occurrence 

 of successive forms of life upon our globe 

 is an historical fact, which cannot be dis- 

 puted ; and the relation of these success- 

 ive forms, as stages of evolution of the 

 same type, is established in various cases. 

 The biologist has no means of determin- 

 ing the time over which the process of 

 evolution has extended, but accepts the 

 computation of the physical geologist 

 and the physicist, whatever that may be. 



Evolution as a philosophical doctrine and phi- 

 losophy. 

 applicable to all phenomena, whether 



physical or mental, whether manifested 



by material atoms or by men in society, 



has been dealt with systematically in the 



