The Force Of These Facts Can Only Be Appreciated When We Come To
Treat The Islands Of The Austro-Malay
Region, and show how
similar barriers have entirely prevented the passage of birds
from one island to another, so that
Out of at least three hundred
and fifty land birds inhabiting Java and Borneo, not more than
ten have passed eastward into Celebes. Yet the Straits of
Macassar are not nearly so wide as the Java sea, and at least a
hundred species are common to Borneo and Java.
I will now give two examples to show how a knowledge of the
distribution of animals may reveal unsuspected facts in the past
history of the earth. At the eastern extremity of Sumatra, and
separated from it by a strait about fifteen miles wide, is the
small rocky island of Banca, celebrated for its tin mines. One of
the Dutch residents there sent some collections of birds and
animals to Leyden, and among them were found several species
distinct from those of the adjacent coast of Sumatra. One of
these was a squirrel (Sciurus bangkanus), closely allied to three
other species inhabiting respectively the Malay peninsula,
Sumatra, and Borneo, but quite as distinct from them all as they
are from each other. There were also two new ground thrushes of
the genus Pitta, closely allied to, but quite distinct from, two
other species inhabiting both Sumatra and Borneo, and which did
not perceptibly differ in these large and widely separated
islands. This is just as if the Isle of Man possessed a peculiar
species of thrush and blackbird, distinct from the birds which
are common to England and Ireland.
These curious facts would indicate that Banca may have existed as
a distinct island even longer than Sumatra and Borneo, and there
are some geological and geographical facts which render this not
so improbable as it would at first seem to be. Although on the
map Banca appears so close to Sumatra, this does not arise from
its having been recently separated from it; for the adjacent
district of Palembang is new land, being a great alluvial swamp
formed by torrents from the mountains a hundred miles distant.
Banca, on the other hand, agrees with Malacca, Singapore, and the
intervening island of Lingen, in being formed of granite and
laterite; and these have all most likely once formed an extension
of the Malay peninsula. As the rivers of Borneo and Sumatra have
been for ages filling up the intervening sea, we may be sure that
its depth has recently been greater, and it is very probable that
those large islands were never directly connected with each other
except through the Malay peninsula. At that period the same
species of squirrel and Pitta may have inhabited all these
countries; but when the subterranean disturbances occurred which
led to the elevation of the volcanoes of Sumatra, the small
island of Banca may have been separated first, and its
productions being thus isolated might be gradually modified
before the separation of the larger islands had been completed.
Enter page number
PreviousNext
Page 104 of 219
Words from 53851 to 54362
of 114260
