The Evolution of the Horse 



rives at more or less justifiable conclusions as to 

 the time which is required for the deposil of a 



certain thickness of rocks; and if he tells me thai 

 the Tertiary formations required 500,000,000 

 years for their deposit, I suppose he has good 

 ground for what he says, and I take that as a 

 measure of the duration of the evolution of the 

 horse from the Orohippus up to its present con- 

 dition. And, if he is right, undoubtedly evolu- 

 tion is a very slow process, and requires a great 

 deal of time. But suppose now, that an astrono- 

 mer or a physicist — for instance, my friend Sir 

 William Thomson — tells me that my geological 

 authority is quite wrong; and that he has weighty 

 evidence to show that life could not possibly have 

 existed upon the surface of the earth 500,000,000 

 years ago, because the earth would have then 1 teen 

 too hot to allow of life, my reply is: "That is not 

 my affair; settle that with the geologist, and when 

 you have come to an agreement among y< >ur- 

 selves I will adopt your conclusions." We take 

 our time from the geologists and physicists, and 

 it is monstrous that, having taken our time 

 from the physical philosopher's clock, the physi- 

 cal philosopher should turn round upon us, and 

 say we are too fast or too slow. What we desire 

 to know is, is it a fact that evolution took place ? 

 As to the amount of time which evolution may 

 have occupied, we are in the hands of the phy- 

 sicist and the astronomer, whose business it is 

 to deal with those questions. 



121 



