396 
GEOGRAPHICAL DISTRIBUTION. 
Chap. XII. 
follow up this subject in all other quarters of the world ; 
but as far as I have gone, the relation generally holds 
good. We see Britain separated by a shallow channel * 
from Europe, and the mammals are the same on both 
sides; we meet with analogous facts on many islands 
separated by similar channels from Australia. The 
West Indian Islands stand on a deeply submerged bank, 
nearly 1000 fathoms in depth, and here we find American 
forms, but the species and even the genera are distinct. 
As the amount of modification in all cases depends to 
a certain degree on the lapse of time, and as during 
changes of level it is obvious that islands separated by 
shallow channels are more likely to have been con¬ 
tinuously united within a recent period to the main¬ 
land than islands separated by deeper channels, we can 
understand the frequent relation between the depth of 
the sea and the degree of affinity of the mammalian 
inhabitants of islands with those of a neighbouring con¬ 
tinent,—an inexplicable relation on the view of inde¬ 
pendent acts of creation. 
All the foregoing remarks on the inhabitants of 
oceanic islands,—namely, the scarcity of kinds—the 
richness in endemic forms in particular classes or sec¬ 
tions of classes,—the absence of whole groups, as of 
batrachians, and of terrestrial mammals notwithstanding 
the presence of aerial bats,—the singular proportions of 
certain orders of plants,—herbaceous forms having been 
developed into trees, &c.,—^seem to me to accord better 
with the view of occasional means of transport having 
been largely efficient in the long course of time, than 
with the view of all our oceanic islands having been 
formerly connected by continuous land with the nearest 
continent; for on this latter view the migration would 
probably have been more complete ; and if modification 
be admitted, all the forms of life would have been more 
