THE EVOLUTION OF MAN 



if we descend still further even into the world 

 of the very low and entirely invertebrate animals. 

 Of course, in practice we shall have to apply, still 

 more than heretofore, what we have previously 

 said about circumstantial evidence. In the first 

 place, one source fails entirely at this point, that 

 of geology. We are compelled to push backward 

 far beyond even the Primary period into the very 

 dimmest time. All direct proofs suddenly fail at 

 this stage. There are no fossils beyond the Pri- 

 mary ones. The minerals of more ancient epochs 

 of the earth's development have been so trans- 

 formed by a process of crystallization, the cause 

 of which we do not yet understand, but which 

 are in some way connected with pressure and 

 heat, that impressions of fossil specimens of 

 former living bones can no longer be discovered 

 in them. Now these so-called crystalline slates 

 are evidently the product of water, hardened sedi- 

 ments of the sea, and there is no reason to assume 

 that the sea in which they were formed contained 

 no living beings at all. On the contrary, there 

 are important reasons contradicting such an as- 

 sumption. The animals of the Primary period 

 are far too highly developed to represent the very 

 first animals on this globe, unless we renounce the 

 idea of development entirely and believe that the 



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