viii 



PEEFACE. 



judge, a real advance has here been made in the mode of treating 

 problems in Geographical Distribution, owing to the firm estab- 

 lishment of a number of preliminary doctrines or " principles," 

 which in many cases lead to a far simpler and yet more com- 

 plete solution of such problems than have been hitherto possible. 

 The most important of these doctrines are those which establish 

 and define — (1) The former wide extension of all groups now 

 discontinuous, as being a necessary result of ''evolution"; 

 (2) The permanence of the great features of the distribution 

 of land and water on the earth's surface ; and, (8) The nature 

 and frequency of climatal changes throughout geological time. 



I have now only to thank the many friends and correspond- 

 ents who have given me information or advice. Besides those 

 whose assistance is acknowledged in the body of the work, I am 

 especially indebted to four gentlemen who have been kind 

 enough to read over the proofs of chapters dealing with ques- 

 tions on which they have special knowledge, giving me the 

 benefit of valuable emendations and suggestions. Mr. Edward 

 R. Alston has looked over those parts of the earlier chapters 

 which relate to the mammals of Europe and the North 

 Temperate zone ; Mr. S. B. J. Skertchley, of the Geological 

 Survey, has read the chapters which discuss the glacial epoch 

 and other geological questions ; Professor A. Newton has looked 

 over the passages referring to the birds of the Madagascar 

 group ; while Sir Joseph D. Hooker has given me the in- 

 valuable benefit of his remarks on my two chapters dealing 

 with the New Zealand flora. 



Cjioydon, August, 1880. 



