DARWIN'S VIEWS OF METHOD. 45 



or detritus, but of a lake dammed up by gla- 

 cial ice. 



Darwin was ashamed of his arguments and 

 conclusions about Glen Roy. "My error," he 

 said, "has been a good lesson to me never to 

 trust in science to the principle of exclusion." l 

 But it is inevitable that apparently definite 

 views should receive just such shocks upon 

 the introduction of a great new principle in a 

 science. The facts that find their explanation 

 under the single newly discovered cause are 

 necessarily referred, before the advent of the 

 new hypothesis, to very various and unrelated 

 causes. 



On the question of the origin of species 

 there were really two hypotheses, creation and 

 descent, when Darwin took hold of it; and he 

 adopted the process of exclusion in treating 

 them. The evidence was all in favor of descent 

 by natural selection and opposed to creation. 

 But he was himself emphatic in the declaration 

 that the origin of species by natural selec- 

 tion was not demonstrated. Belief in it must 

 be based on general considerations, that 

 natural selection is an actually existing cause, 

 and that it explains a host of facts and brings 

 them under one point of view. One hypothesis 



1 Life and Letters, Vol. I. p. 57. 



