OF GEOLOGICAL DYNAMICS. 89 



hypotheses which could not now be justly adduced 

 to support such estimates when physical geology 

 declares against them. I am glad to find this view 

 supported by the high authority of Professor 

 Huxley himself, who says, "But it may be said 

 " that it is biology and not geology which asks for 

 " so much time that the succession of life demands 

 " vast intervals ; but this appears to me to be 

 " reasoning in a circle. Biology takes her time 

 "from geology. The only reason we have for 

 " believing in the slow rate of the change in 

 " living forms is the fact that they persist through 

 "a series of deposits which geology informs us 

 "have taken a long while to make. If the geo- 

 " logical clock is wrong, all the naturalist will have 

 " to do is to modify his notions of the rapidity of 

 "change accordingly." But I may be permitted 

 to remark that a correction of this kind cannot be 

 said to be unimportant in reference to biological 

 speculation. The limitation of geological periods, 

 imposed by physical science, cannot, of course, 

 disprove the hypothesis of transmutation of species ; 

 but it does seem sufficient to disprove the doctrine 



