ORGANIC GEOLOGICAL DYNAMICS. 623 



of research, the creation of living things ; a subject 

 shrouded in mystery, and not to be approached 

 without reverence. But though we may conceive, 

 that, on this subject, we are not to seek our belief 

 from science alone, we shall find, it is asserted, 

 within the limits of allowable and unavoidable spe- 

 culation, many curious and important problems 

 which may well employ our physiological skill. For 

 example, we may ask: how we are to recognize 

 the species which were originally created distinct? 

 whether the population of the earth at one geo- 

 logical epoch could pass to the form which it has 

 at a succeeding period, by the agency of natural 

 causes alone ? and if not, what other account we 

 can give of the succession which we find to have 

 taken place? 



The most remarkable point in the attempts to 

 answer these and the like questions, is the contro- 

 versy between the advocates and the opponents of 

 the doctrine of the transmutation of species. This 

 question is, even from its mere physiolo'gical im- 

 port, one of great interest ; and the interest is much 

 enhanced by our geological researches, which again 

 bring the question before us in a striking form, and 

 on a gigantic scale. We shall, therefore, briefly 

 state the point at issue. 



Sect. 3. Question of the Transmutation of Species. 



WE see that animals and plants may, by the influ- 

 ence of breeding, and of external agents operating 



