CHAPTER XV. 



THE DISTRIBUTION OF ANIMALS AND PLANTS 



AS RELATED TO GEOGRAPHICAL AND 



GEOLOGICAL CHANGES. 



A^L are now agreed that to explain the extraordinary and 

 often apparently anomalous distribution of animals and 

 plants over the surface of the earth, and the occurrence of 

 like forms in very distant localities, and even on islands 

 separated by vast stretches of ocean from one another and 

 from the continents, we must invoke the aid of geology. We 

 must have reference to those changes of climate and of eleva- 

 tion which have occurred in the more recent periods of the 

 earth's history, and must carry with us the idea, at first not 

 apparently very reasonable, that living beings have existed 

 much longer than many of the lands which they inhabit, 

 or at least than the present state of those lands in reference 

 to isolation or continental connection. To what extent we 

 may further require to call in the aid of varietal or specific 

 modification to explain the facts, may be more doubtful ; and 

 I think we shall find that a larger acquaintance with geological 

 truths would enable us to dispense with the aid of hypotheses 

 of evolution, at least in so far as the local establishment ot 

 new generic and specific types is concerned. 



One of the most remarkable and startling results of geo- 

 logical investigation, and one which must be accepted as an 

 established fact, independently of all theoretical explanations, 

 is that the earth has experienced enormous revolutions of 



