In such well-known families as the woodpeckers, parrots, trogons, barbets, kingfishers, pigeons, and pheasants, we find some identical species spreading over all India, and as far as Java and Borneo, while a very large proportion are common to Sumatra and the Malay peninsula.
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.