But In These Cases The Number Of
Species That Have Thus Migrated Will Be Very Small, And There
Will Be Great Deficiencies Even In Birds And Flying Insects,
Which We Should Imagine Could Easily Cross Over.
The island of
Timor (as I have already shown in Chapter XIII) bears this
relation to Australia; for while
It contains several birds and
insects of Australian forms, no Australian mammal or reptile is
found in it, and a great number of the most abundant and
characteristic forms of Australian birds and insects are entirely
absent. Contrast this with the British Islands, in, which a large
proportion of the plants, insects, reptiles, and Mammalia of the
adjacent parts of the continent are fully represented, while
there are no remarkable deficiencies of extensive groups, such as
always occur when there is reason to believe there has been no
such connexion. The case of Sumatra, Borneo, and Java, and the
Asiatic continent is equally clear; many large Mammalia,
terrestrial birds, and reptiles being common to all, while a
large number more are of closely allied forms. Now, geology has
taught us that this representation by allied forms in the same
locality implies lapse of time, and we therefore infer that in
Great Britain, where almost every species is absolutely identical
with those on the Continent, the separation has been very recent;
while in Sumatra and Java, where a considerable number of the
continental species are represented by allied forms, the
separation was more remote.
From these examples we may see how important a supplement to
geological evidence is the study of the geographical distribution
of animals and plants, in determining the former condition of the
earth's surface; and how impossible it is to understand the
former without taking the latter into account. The productions of
the Aru Islands offer the strangest evidence, that at no very
distant epoch they formed a part of New Guinea; and the peculiar
physical features which I have described, indicate that they must
have stood at very nearly the same level then as they do now,
having been separated by the subsidence of the great plain which
formerly connected them with it.
Persons who have formed the usual ideas of the vegetation of the
tropics who picture to themselves the abundance and brilliancy of
the flowers, and the magnificent appearance of hundreds of forest
trees covered with masses of coloured blossoms, will be surprised
to hear, that though vegetation in Aru is highly luxuriant and
varied, and would afford abundance of fine and curious plants to
adorn our hothouses, yet bright and showy flowers are, as a
general rule, altogether absent, or so very scarce as to produce
no effect whatever on the general scenery. To give particulars: I
have visited five distinct localities in the islands, I have
wandered daily in the forests, and have passed along upwards of a
hundred miles of coast and river during a period of six months,
much of it very fine weather, and till just as I was about to
leave, I never saw a single plant of striking brilliancy or
beauty, hardly a shrub equal to a hawthorn, or a climber equal to
a honeysuckle!
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