In The Islands Between Timor And Java There Is Often
A More Thickly Wooded Country Abounding In Thorny And Prickly
Trees.
These seldom reach any great height, and during the force
of the dry season they almost completely lose their leaves,
allowing the ground beneath them to be parched up, and
contrasting strongly with the damp, gloomy, ever-verdant forests
of the other islands.
This peculiar character, which extends in a
less degree to the southern peninsula of Celebes and the east end
of Java, is most probably owing to the proximity of Australia.
The south-east monsoon, which lasts for about two-thirds of the
year (from March to November), blowing over the northern parts of
that country, produces a degree of heat and dryness which
assimilates the vegetation and physical aspect of the adjacent
islands to its own. A little further eastward in Timor and the Ke
Islands, a moister climate prevails; the southeast winds blowing
from the Pacific through Torres Straits and over the damp forests
of New Guinea, and as a consequence, every rocky islet is clothed
with verdure to its very summit. Further west again, as the same
dry winds blow over a wider and wider extent of ocean, they have
time to absorb fresh moisture, and we accordingly find the island
of Java possessing a less and less arid climate, until in the
extreme west near Batavia, rain occurs more or less all the year
round, and the mountains are everywhere clothed with forests of
unexampled luxuriance.
Contrasts in Depth of Sea. - It was first pointed out by Mr.
George Windsor Earl, in a paper read before the Royal
Geographical Society in 1845, and subsequently in a pamphlet "On
the Physical Geography of South-Eastern Asia and Australia",
dated 1855, that a shallow sea connected the great islands of
Sumatra, Java, and Borneo with the Asiatic continent, with which
their natural productions generally agreed; while a similar
shallow sea connected New Guinea and some of the adjacent islands
to Australia, all being characterised by the presence of
marsupials.
We have here a clue to the most radical contrast in the
Archipelago, and by following it out in detail I have arrived at
the conclusion that we can draw a line among the islands, which
shall so divide them that one-half shall truly belong to Asia,
while the other shall no less certainly be allied to Australia. I
term these respectively the Indo-Malayan and the Austro-Malayan
divisions of the Archipelago.
On referring to pages 12, 13, and 36 of Mr. Earl's pamphlet, it
will be seen that he maintains the former connection of Asia and
Australia as an important part of his view; whereas, I dwell
mainly on their long continued separation. Notwithstanding this
and other important differences between us, to him undoubtedly
belongs the merit of first indicating the division of the
Archipelago into an Australian and an Asiatic region, which it
has been my good fortune to establish by more detailed
observations.
Contrasts in Natural Productions. - To understand the importance
of this class of facts, and its bearing upon the former
distribution of land and sea, it is necessary to consider the
results arrived at by geologists and naturalists in other parts
of the world.
It is now generally admitted that the present distribution of
living things on the surface of the earth is mainly the result of
the last series of changes that it has undergone. Geology teaches
us that the surface of the land, and the distribution of land and
water, is everywhere slowly changing. It further teaches us that
the forms of life which inhabit that surface have, during every
period of which we possess any record, been also slowly changing.
It is not now necessary to say anything about how either of those
changes took place; as to that, opinions may differ; but as to
the fact that the changes themselves have occurred, from the
earliest geological ages down to the present day, and are still
going on, there is no difference of opinion. Every successive
stratum of sedimentary rock, sand, or gravel, is a proof that
changes of level have taken place; and the different species of
animals and plants, whose remains are found in these deposits,
prove that corresponding changes did occur in the organic world.
Taking, therefore, these two series of changes for granted, most
of the present peculiarities and anomalies in the distribution of
species may be directly traced to them. In our own islands, with
a very few trifling exceptions, every quadruped, bird, reptile,
insect, and plant, is found also on the adjacent continent. In
the small islands of Sardinia and Corsica, there are some
quadrupeds and insects, and many plants, quite peculiar. In
Ceylon, more closely connected to India than Britain is to
Europe, many animals and plants are different from those found in
India, and peculiar to the island. In the Galapagos Islands,
almost every indigenous living thing is peculiar to them, though
closely resembling other kinds found in the nearest parts of the
American continent.
Most naturalists now admit that these facts can only be explained
by the greater or less lapse of time since the islands were
upraised from beneath the ocean, or were separated from the
nearest land; and this will be generally (though not always)
indicated by the depth of the intervening sea. The enormous
thickness of many marine deposits through wide areas shows that
subsidence has often continued (with intermitting periods of
repose) during epochs of immense duration. The depth of sea
produced by such subsidence will therefore generally be a measure
of time; and in like manner, the change which organic forms have
undergone is a measure of time. When we make proper allowance for
the continued introduction of new animals and plants from
surrounding countries by those natural means of dispersal which
have been so well explained by Sir Charles Lyell and Mr. Darwin,
it is remarkable how closely these two measures correspond.
Britain is separated from the continent by a very shallow sea,
and only in a very few cases have our animals or plants begun to
show a difference from the corresponding continental species.
Corsica and Sardinia, divided from Italy by a much deeper sea,
present a much greater difference in their organic forms.
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