Geographical Distribution. 223 
slight, because the time allowed for it has been so 
short. But the longer the time that a colony of a 
species is thus completely isolated under changed 
conditions of life the greater, according to the evolu- 
tion theory, should we expect the change to become. 
Therefore, in all cases where we happen to know, 
from independent evidence of a geological kind, that 
an oceanic island is of very ancient formation, the 
evolution theory would expect to encounter a 
great wealth of peculiar species. On the other 
hand, as I have just observed, the special-creation 
theory can have no reason to suppose that there 
should be any correlation between the age of an 
oceanic island and the number of peculiar species 
which it may be found to contain. 
Therefore, having considered the principles of geo- 
graphical distribution from the widest or most gencral 
point of view, we shall pass to the opposite extreme, 
and consider exhaustively, or in the utmost possible 
detail, the facts of such distribution where the con- 
ditions are best suited to this purpose—that is, as I 
have already said, upon oceanic islands, which may be 
metaphorically regarded as having been formed by 
nature for the particular purpose of supplying natura- 
lists with a crucial test between the theories of 
creation and evolution. The material upon which my 
analysis is to be based will be derived from the most 
recent works upon geographical distribution—espe- 
cially from the magnificent contributions to this depart- 
ment of science which we owe to the labours of Mr. 
Wallace. Indeed, all that follows may be regarded as 
a condensed filtrate of the facts which he has collected. 
Even as thus restricted, however, our subject-matter 
