Borneo is one of the largest islands of the world. Its area is
roughly 290,000 square miles, or about five times that of England
and Wales. Its greatest length from north-east to south-west is 830
miles, and its greatest breadth is about 600 miles. It is crossed
by the equator a little below its centre, so that about two-thirds
of its area lie in the northern and one-third lies in the southern
hemisphere. Although surrounded on all sides by islands of volcanic
origin, Borneo differs from them in presenting but small traces of
volcanic activity, and in consisting of ancient masses of igneous
rock and of sedimentary strata.

The highest mountain is Kinabalu, an isolated mass of granite in the
extreme north, nearly 14,000 feet in height. With this exception the
principal mountains are grouped in several massive chains, which
rise here and there to peaks about 10,000 feet above the sea. The
principal of these chains, the Tibang-Iran range, runs south-westward
through the midst of the northern half of the island and is prolonged
south of the equator by the Schwaner chain. This median south-westerly
trending range forms the backbone of the island. A second much-broken
chain runs across the island from east to west about 1[degree]
north of the equator. Besides these two principal mountain chains
which determine the main features of the river-system, there are
several isolated peaks of considerable height, and a minor ridge of
hills runs from the centre towards the south-cast corner. With the
exception of the northern extremity, which geographically as well
as politically stands apart from the rest of the island, the whole
of Borneo may be described as divided by the two principal mountain
chains into four large watersheds. Of these, the north-western basin,
the territory of Sarawak, is drained by the Rejang and Baram, as well