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, (3) 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. 
Croydon, August , 1880. 
