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.
As the southern part of Sumatra extended eastward and formed the narrow
straits of Banca, many birds and insects and some Mammalia would
123