II THE PROGRESS OF SCIENCE 125 



merits, and have obtained stores of information 

 of the greatest value. For the first time, we 

 are in possession of something like precise know- 

 ledge of the physical features of the deep seas, 

 and of the living population of the floor of the 

 ocean. The careful and exhaustive study of the 

 phenomena presented by the accumulations of 

 snow and ice, in polar and mountainous 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 pro- 

 duced effects, formerly confidently referred to 

 diluvial catastrophes, but it has suggested new 

 methods of accounting for various puzzling facts 

 of distribution. 



Palaeontology, which treats of the extinct 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 

 wonderful development in our epoch. In some 

 groups of animals and plants, the extinct repre- 

 sentatives, already known, are more numerous 

 and important than the living. There can be no 

 doubt that the existing Fauna and Flora is but 

 the last term of a long series of equally numerous 

 contemporary species, which have succeeded one 

 another, by the slow and gradual substitution of 

 species for species, in the vast interval of time 

 which has elapsed between the deposition of the 

 earliest fossiliferous strata and the present day. 



