Mr. Windsor Earl has made some striking
observations on this head in regard to the great Malay Archipelago,
which is traversed near Celebes by a space of deep ocean; and this
space separates two widely distinct mammalian faunas. 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 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.
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