IN THE LAST HALF-CENTURY. 133 



aincras regions, which has taken place in 

 our time, has not only revealed to the 

 geologist an agent of denudation and 

 transport, which has slowly and quietly 

 produced effects, formerly confidently re- 

 ferred to diluvial catastrophes, but it has 

 suggested new methods of accounting for 

 various puzzling facts of distribution. 



Palaeontology, which treats of the ex- Palason- 

 tinct forms of life and their succession 

 and distribution upon our globe, a branch 

 of science which could hardly be said to 

 exist a century ago, has undergone a won- 

 derful development in our epoch. In 

 some groups of animals and plants, the 

 extinct representatives, already known, 

 are more numerous and important than 

 the living. There can be no doubt that 

 the existing Fauna and FJora is but the 

 last term of a long series of equally nu- 

 merous contemporary species, which have 

 succeeded one another, by the slow and 

 gradual substitution of species for species, 



