The Pagan Tribes of Borneo | Page 9

longer course to the rivers of that part, in spite of the fact that all the six principal rivers mentioned above have their sources not far from this central point. The principal rivers thus radiate from a common centre, the Batang Kayan flowing east-north-east, the Kotei south-east by east, the Banjermasin south, the Kapuas a little south of west, the Rejang west, and the Baram north-west. This radiation of the rivers from a common centre is a fact of great importance for the understanding of the ethnography of the island, since the rivers are the great highways which movements of the population chiefly follow.
In almost all parts of the island, the land adjoining the coast is a low-lying swampy belt consisting of the alluvium brought down by the many rivers from the central highlands. This belt of alluvium extends inland in many parts for fifty miles or more, and is especially extensive in the south and south-east of the island.
Between the swampy coast belt and the mountains intervenes a zone of very irregular hill country, of which the average height above the sea-level is about one thousand feet, with occasional peaks rising to five or six thousand feet or more.
There seems good reason to believe that at a comparatively recent date Borneo was continuous with the mainland of Asia, forming its south-eastern extremity. Together with Sumatra and Java it stands upon a submarine bank, which is nowhere more than one hundred fathoms below the surface, but which plunges down to a much greater depth along a line a little east of Borneo (Wallace's line). The abundance of volcanic activity in the archipelago marks it as a part of the earth's crust liable to changes of elevation, and the accumulation of volcanic matter would tend to make it an area of subsidence; while the north-east monsoon, which blows with considerable violence down the China Sea for about four months of each year, may have hastened the separation of Borneo from the mainland. That this separation was effected in a very recent geological period is shown by the presence in Borneo of many species of Asiatic mammals both large and small, notably the rhinoceros (R. BORNIENSIS, closely allied to R. SUMATRANUS); the elephant (E. INDICUS, which, however, may have been imported by man); the wild cattle (BOS SONDIACUS, which occurs also in Sumatra); several species of deer and pig (some of which are found in Sumatra and the mainland); several species of the cat tribe, of which the tiger-cat (FELIS NEBULOSA) is the largest; the civet-cat (VIVERRA) and its congeners HEMIGALE, PARADOXURUS, and ARCTOGALE; the small black bear (URSUS MALAYANUS); the clawless otter (LUTRA CINEREA); the bear-cat (ARCTICTIS BINTURONG); the scaly ant-eater (MANIS JAVANICUS); the lemurs (TARSIUS SPECTRUM and NYCTICEBUS TARDIGRADUS); the flying lemur (GALEOPITHECUS VOLANS); the porcupine (HYSTRIX CRASSISPINIS); numerous bats, squirrels, rats and mice; the big shrew (GYMNURA); several species of monkeys, and two of the anthropoid apes. The last are of peculiar significance, since they are incapable of crossing even narrow channels of water, and must be regarded as products of a very late stage of biological evolution. Of these two anthropoid species, the gibbon (HYLOBATES MULLERI) is closely allied to species found in the mainland and in Sumatra, while the MAIAS or orang-utan (SIMIA SALYRUS) is found also in Sumatra and, though not now surviving on the continent, must be regarded as related to anthropoids whose fossil remains have been discovered there.[2]
The zoological evidence thus indicates a recent separation of Borneo and Sumatra from the continent, and a still more recent separation between the two islands.
The climate of the whole island is warm and moist and very equable. The rainfall is copious at all times of the year, but is rather heavier during the prevalence of the north-east monsoon in the months from October to February, and least during the months of April and May. At Kuching, during the last thirty years, the average yearly rainfall has been 160 inches, the maximum 225, and the minimum 102 inches; the maximum monthly fall recorded was 69 inches, and the minimum .66, and the greatest rainfall recorded in one day was 15 inches. The temperature hardly, if ever, reaches 100[degree] F.; it ranges normally between 70[degree] and 90[degree] F.; the highest reading of one year (1906) at Kuching was 94[degree], the lowest 69[degree]. Snow and frost are unknown, except occasionally on the summits of the highest mountains. Thunder-storms are frequent and severe, but wind-storms are not commonly of any great violence.
The abundant rainfall maintains a copious flow of water down the many rivers at all times of the year; but the rivers are liable to rise rapidly many feet above their normal level during days of exceptionally heavy rain. In their lower reaches, where they traverse the alluvial plains and