s. On either side the islands are situated on
moderately deep submarine banks, and they are inhabited by closely allied
or identical quadrupeds. No doubt some few anomalies occur in this great
archipelago, and there is much difficulty in forming a judgment in some
cases owing to the probable naturalisation of certain mammals through man's
agency; but we shall soon have much light thrown on the natural history of
this archipelago by the admirable zeal and researches of Mr. Wallace. I
have not as yet had time to {396} 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
continuously united within a recent period to the mainland 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 continent,--an
inexplicable relation on the view of independent 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 sections 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 {397} equally modified, in accordance with the paramount
importance of the rela