HISTORY OF THE THEORY OF EVOLUTION 23 



which in 1830 proved fatal, and which led to the 

 triumph of Catastrophism over Evolution. The sup- 

 porters of Evolution were silenced, but not convinced. 

 In France the defeat was complete, but not so in 

 other countries. It was clear that the attack must 

 be made along new lines if there were to be any 

 prospect of success. This fatal objection must be 

 met. Was it not possible to determine the causes ? 

 and if so, how ? What could we hope to know of 

 causes which could lead to modifications in animals 

 of former geologic ages ? Yet the answer was at 

 hand, for seven months before Cuvier's final triumph 

 at the Academy of Paris on July 19, 1830, ap- 

 peared the first volume of Lyell's " Principles of 

 Geology," in which the true path was indicated, and 

 the key to the past shown to be afforded by the 

 study of the present. If we would know what 

 happened in former times, we should look around us 

 and see what is taking place before our eyes. In 

 this way Lyell gauged the forces of Nature — the 

 power of running water, the force of the tides, the 

 effect of frost and heat, the slow movements of 

 upheaval and subsidence, the slow change of climate 

 due to astronomical causes. He was able to prove 

 that causes now acting, and causes which must have 

 been in action from immeasurably remote periods, 

 were competent to produce the effects we wonder 

 at — the upheaval of mountain ranges, the excavation 

 of valleys, &c. — without any need for external or 

 supernatural agencies, and indeed, leaving no room 

 for such agencies, for then there was nothing further 

 to accomplish. The final stroke was given by 



