ORGANIC GEOLOGICAL DYNAMICS. 625 



And the dilemma then presents itself to us anew: 

 either we must accept the doctrine of the transmu- 

 tation of species, and must suppose that the organ- 

 ized species of one geological epoch were trans- 

 muted into those of another by some long-continued 

 agency of natural causes ; or else, we must believe 

 in many successive acts of creation and extinction 

 of species, out of the common course of nature ; acts 

 which, therefore, we may properly call miraculous. 



This latter dilemma, however, is a question con- 

 cerning the facts which have happened in the his- 

 tory of the world; the deliberation respecting it 

 belongs to physical geology itself, and not to that 

 subsidiary science which we are now describing, 

 and which is concerned only with such causes as 

 we know to be in constant and orderly action. 



The former question, of the limited or unlimited 

 extent of the modifications of animals and plants, 

 has received full and careful consideration from 

 eminent physiologists : and in their opinions we 

 find, I think, an indisputable preponderance to 

 that decision which rejects the transmutation of 

 species, and which accepts the former side of the 

 dilemma ; namely, that the changes of which each 

 species is susceptible, though difficult to define in 

 words, are limited in fact. It is extremely interest- 

 ing and satisfactory thus to receive an answer in 

 which we can confide, to inquiries seemingly so 

 wide and bold as those which this subject involves. 

 I refer to Mr. Lyell, Dr. Prichard, Mr. Lawrence, 

 VOL. in. S s 



