PREFACE TO FIRST EDITION 



generally that, so far as I am able to judge, a real 

 advance has here been made in the mode of treating 

 problems in Geographical Distribution, owing to the firm 

 establishment of a number of preliminary doctrines or 

 " principles," which in many cases lead to a far simpler and 

 yet more complete 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, (3) The nature and 

 frequency of climatal changes throughout geological time. 



I have now only to thank the many friends and 

 correspondents 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 chap- 

 ters dealing with questions 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 invaluable 

 benefit of his remarks on my two chapters dealing with the 

 New Zealand flora. 



Croydon, August^ 1880. 



