164 
ZOOLOGICAL GEOGRAPHY. 
[part III. 
which have been founded on supposed difficulties in the distri- 
bution of animals in space and time. 
It also illustrates and supports the geological doctrine, of the 
general permanence of our great continents and oceans, by 
showing how many facts in the distribution of animals can 
only be explained and understood on such a supposition ; and 
it exhibits, in a striking manner, the enormous influence of the 
Glacial epoch, in determining the existing zoological features of 
the various continents. 
And, lastly, it furnishes a more consistent and intelligible 
idea than has yet been reached by any other mode of investiga- 
tion, of all the more important changes of the earth’s surface 
that have probably occurred during the entire Tertiary period ; 
and of the influence of these changes, in bringing about the 
general features, as well as many of the more interesting details 
and puzzling anomalies, of the Geographical Distribution of 
Animals. 
