CHAP. XX. HOW FAR ANSWERED. 393 



entertained of the extent of past time by most of the ablest 

 g-eologists, and when great revolutions of the earth's crust, 

 and its inhabitants, were generally attributed to sudden and 

 violent catastrophes. 



While, in 1832, I argued against Lamarck's doctrine of the 

 gradual transmutation of one species into another, I agreed 

 with him in believing that the system of changes now in 

 progress in the oi'ganic world would afford, when fully under- 

 stood, a complete key to the interpretation of all the vicissi- 

 tudes of the living creation in past ages. I contended against 

 the doctrine, then very popular, of the sudden destruction of 

 vast multitudes of species, and the abruj)t ushering into the 

 world of new batches of plants and animals. 



I endeavored to sketch out (and it was, I believe, the first 

 systematic attempt to accomplish such a task) the laws 

 which govern the extinction of species, with a view of show- 

 ing that the slow but ceaseless variations now in progress 

 in phj^sical geography, together with the migration of plants 

 and animals into new regions, must, in the course of ages, 

 give rise to the occasional loss of some of them, and eventually 

 cause an entire fauna and flora to die out ; also, that we must 

 infer, from geological data, that the places thus left vacant 

 from time to time are filled up without delay by new forms, 

 adapted to new conditions, sometimes by immigration from 

 adjoining provinces, sometimes by new creations. Among 

 the many causes of extinction enumerated by me, were the 

 power of hostile species, diminution of food, mutations in 

 climate, the conversion of land into sea, and of sea into land, 

 &G. I firmly opposed Brocchi's hypothesis, of a decline in 

 the vital energy of each species;* maintaining that there 

 was every reason to believe that the reproductive powers of 

 the last surviving representatives of a species were as 



* Principles of Geology, 1st ed. ch. viii. vol. ii. ; and 9th ed. p. 668. 



