m 



CHAPTER XIX. 



DARWINISM CONTINUED. 



How Change is Produced — Vast Eras of Time — The Age of the 

 Earth — Evidences of Evolution — Extinct Animals. 



N the previous chapter we 

 have seen that Darvvin 

 claims that in nature there 

 is a tendency to varia- 

 biHty, certain conditions 

 producing it, and that all 

 the diverse forms of ani- 

 mal life are to-day the 

 result of this process. 

 Without an adequate idea 

 of geological time this 

 cannot be realized ; but 

 if we imagine that these changes have gradually been 

 going on for unknown ages, periods which the mind 

 of man cannot grasp, we begin to see the light ahead 

 that Darvvin saw. 



In the present age geology and palaeontology, or 

 the history of extinct animals, through the investiga- 

 tions of Professors Cope, Marsh, Leidy in this country, 



183 



