Rivers.—The rivers play a very important part in the economy of Borneo, both as highways and as lines along which run the main arteries of population. Hydrographically the island may be divided into five principal versants. Of these the shortest embraces the north-western slope, north of the Kapuas range, and discharges its waters into the China Sea. The most important of its rivers are the Sarawak, the Batang-Lupar, the Sarebas, the Rejang (navigable for more than 100 m.), the Baram, the Limbang or Brunei river, and the Padas. The rivers of British North Borneo to the north of the Padas are of no importance and of scant practical utility, owing to the fact that the mountain range here approaches very closely to the coast with which it runs parallel. In the south-western versant the largest river is the Kapuas, which, rising near the centre of the island, falls into the sea between Mampawa and Sukadana after a long and winding course. This river, of volume varying with the tide and the amount of rainfall, is normally navigable by small steamers and native prahus, of a draught of 4 to 5 ft., for 300 to 400 m., that is to say, from Pontianak up to Sintang, and thence as far as Benut. The middle part of this river, wider and more shallow than the lower reaches, gives rise to a region of inundation and lakes which extend as far as the northern mountain chain. Among its considerable tributaries may be mentioned the southern Melawi with its affluent the Penuh. It reaches the sea through several channels in a wide marshy delta. The Sambas, north of the Kapuas, is navigable in its lower course for vessels drawing 25 ft. Rivers lying to the south of the Kapuas, but of less importance in the way of size, commerce and navigation, are the Simpang, Pawanand Kandawangan, in the neighbourhood of whose mouths, or upon the adjacent coast, the principal native villages are situated in each case. The Barito, which is the principal river of the southern versant, takes its rise in the Kuti Lama Lake, and falls into the Java Sea in 114° 30′ E. Its upper reaches are greatly impeded by rocks, rapids and waterfalls, but the lower part of its course is wide, and traverses a rich, alluvial district, much of which is marshy. Cross branches unite it with two rivers of considerable size towards the west, the Kapuas Murung or Little Dyak, and the Kahayan or Great Dyak. The Katingan or Mendawei, the Sampit, Pembuang or Surian and the Kota Waringin are rivers that fall into the sea farther to the west. The rivers of the southern versant are waters of capacious drainage, the basin of the Kahayan having, for instance, an area of 16,000 sq. m., and the Barito one of 38,000 sq. m. These rivers are navigable for two-thirds of their course by steamers of a fair size, but in many cases the bars at their mouths present considerable difficulties to ships drawing anything over 8 or 9 ft. Most of the larger affluents of the Barito are also navigable throughout the greater part of their courses. The south-eastern like the north-western corner of the island is watered by a considerable number of short mountain streams. The one great river of the eastern versant is the Kutei or Mahakan, which, rising in the central mountains, flows east with a sinuous course and falls by numerous mounts into the Straits of Madassar. At a great distance from its mouth it has still a depth of three fathoms, and in all its physical features it is comparable to the Kapuas and Barito. The Kayan or Bulungan river is the only other in the eastern versant that calls for mention. Most of the rivers of the northern versant are comparatively small, as the island narrows into a kind of promontory. Of these the Kinabatangan in the territory of British North Borneo is the most important. Lakes are neither numerous nor very large. In most cases they are more fittingly described as swamps. In the flood area of the upper Kapuas, of which mention has already been made, there occurs Lake Luar, and there are several lake expanses of a similar character in the basins of the Barito and Kutei rivers. The only really fine natural harbour in the island of which any use has been made is that of Sandakan, the principal settlement of the North Borneo Company on the north coast.
Geology.—The geology of Borneo is very imperfectly known. The mountain range which lies between Sarawak and the Dutch possessions, and may be looked upon as the backbone of the island, consists chiefly of crystalline schists, together with slates, sandstones and limestones. All these beds are much disturbed and folded. The sedimentary deposits were formerly believed to be Palaeozoic, but Jurassic fossils have since been found in them, and it is probable that several different formations are represented. Somewhat similar rocks appear to form the axis of the range in south-east Borneo, and possibly of the Tampatung Mountains. But the Müller range, the Madi plateau, and the Schwaner Mountains of west Borneo, consist chiefly of almost undisturbed sedimentary and volcanic rocks of Tertiary age. The low-lying country between the mountain ranges is covered for the most part by Tertiary and Quaternary deposits, but Cretaceous beds occur at several localities. Some of the older rocks of the mountain regions have been referred to the Devonian, but the evidence cannot be considered conclusive. Vertebraria and Phyllotheca, plants characteristic of the Indian Gondwana series, have been recorded in Sarawak; and marine forms, similar to those of the lower part of the Australian Carboniferous system, are stated to occur in the limestone of north Borneo. Pseudomonotis salinaria, a Triassic form, has been noted from the schists of the west of Borneo. In the Kapoewas district radiolarian cherts supposed to be of Jurassic age are met with. Undoubted Jurassic fossils, belonging to several horizons, have been described from west Borneo and Sarawak. The Cretaceous beds, which have long been known in west Borneo, are comparatively little disturbed. They consist for the most part of marls with Orbitolina concava, and are referred to the Cenomanian. Cretaceous beds of somewhat later date are found in the Marpapura district in south-east Borneo. The Tertiary system includes conglomerates, sandstones, limestones and marls, which appear to be of Eocene, Oligocene and Miocene age. They contain numerous seams of coal. The Tertiary beds generally lie nearly horizontal and form the lower hills, but in the Madi plateau and the Schwaner range they rise to a height of several thousand feet. Volcanic rocks of Tertiary and late Cretaceous age are extensively developed, especially in the Müller Mountains. The whole of this consists of tuffs and lavas, andesites prevailing in the west and rhyolites and dacites in the east.
Minerals.—The mineral wealth of Borneo is great and varied. It includes diamonds, the majority of which, however, are of a somewhat yellow colour, gold, quicksilver, cinnabar, copper, iron, tin, antimony, mineral oils, sulphur, rock-salt, marble and coal. The exploitation of the mines suffers in many cases from the difficulties and expense of transport, the high duties payable in Dutch Borneo to the native princes, the competition among the rival companies, and often the limited quantities of the minerals found in the mines. The districts of Sambas and Landak in the west, the Kahayan river, the mountain valleys of the extreme south-east and parts of Sarawak furnish the largest quantities of gold, which is obtained for the most part from alluvial washings. The Borneo Company is engaged in working gold-mines in the upper part of the Sarawak valley, and the prospects of the enterprise, which is conducted on a fairly extensive scale, are known to be encouraging. Diamonds are also found widely distributed and mainly in the same regions as the gold. The Kapuas valley has so far yielded the largest quantity, and Pontianak is, for diamonds, the principal port of export. Considerable progress has been made in the development of the oil-fields in Dutch Borneo, and the Nederlandsch Indische Industrie en Handel Maatschappij, the Dutch business of the Shell Transport and Trading Company, increased its output from 123,592 tons in 1901 to 285,720 tons in 1904, and showed further satisfactory increase thereafter. This company owns extensive oil-fields at Balik Papan and Sanga-Sanga. The quality of the oil varies in a remarkable way according to the depth. The upper stratum is struck at a depth of 600 to 700 ft., and yields a natural liquid fuel of heavy specific gravity. The next source is met with at about 1200 ft., yielding an oil which is much lighter in weight and, as such, more suitable for treatment in the refinery. The former oil is almost invariably of an asphalte basis, whereas the latter sometimes is found to contain a considerable percentage of paraffin wax. The average daily production is very high, owing to a large number of the wells flowing under the natural pressure of the gas. There is every reason to believe that the oil-fields of Dutch Borneo have a great future. Coal mines have, in many instances, been opened and abandoned, failure being due to the difficulty of production. Coal of good quality has been found in Pengaron and elsewhere in the Banjermasin district, but most Borneo coal is considerably below this average of excellence. It has also been found in fair quantities at various places in the Kutei valley and in Sarawak. The coalmines of Labuan have been worked spasmodically, but success has never attended the venture. Sadong yields something under 130 tons a day, and the Brooketown mine, the property of the raja of Sarawak, yields some 50 tons a day of rather indifferent coal. The discovery that Borneo produced antimony was made in 1825 by John Crawfurd, the orientalist, who learned in that year that a quantity had been brought to Singapore by a native trader as ballast. The supply is practically unlimited and widely distributed. The principal mine is at Bidi in Sarawak.
Climate and Health.—As is to be anticipated, having regard to its insular position and to the fact that the equator passes through the very middle of the island, the climate is at once hot and very damp. In the hills and in the interior regions are found which may almost be described as temperate, but on the coasts the atmosphere is dense, humid and oppressive. Throughout the average temperature is from 78° to 80° F., but the thermometer rarely falls below 70°, except in the hills, and occasionally on exceptional days mounts as high as 96° in the shade. The rainy westerly winds (S.W. and N.W.) prevail at all the meteorological stations, not the comparatively dry south-east wind. Even at Banjermasin, near the south coast, the north-west wind brings annually a rainfall of 60 in., as against 33 in. of rain carried by the south-east wind. The difference between the seasons is not rigidly marked. The climate is practically unchanging all the year round, the atmosphere being uniformly moist, and though days of continuous downpour are rare, comparatively few days pass without a shower. Most rain falls between November and May, and at this season the torrents are tremendous while they last, and squalls of wind are frequent and violent, almost invariably preceding a downpour. Over such an extensive area there is, of course, great variety in the climatic character of different districts, especially when viewed in relation to health. Some places, such as Bidi in Sarawak, for instance, are notoriously unhealthy; but from the statistics of the Dutch government, and the records of Sarawak and British North Borneo, it would appear that the European in Borneo has in general not appreciably more to fear than his fellow in Java, or in the Federated Malay States of the Malayan Peninsula. Among the native races the prevailing diseases, apart from those of a malarial origin, are chiefly such as arise from bad and insufficient food, from intemperance, and from want of cleanliness. The habit of allowing their meat to putrefy before regarding it as fit for food, and of encouraging children of tender age to drink to intoxication, accounts for absence of old folk and the heavy mortality which are to be observed among the Muruts of British North Borneo and some of the other more debased tribes of the interior of the island. Scrofula and various forms of lupus are common among the natives throughout the country and especially in the interior; elephantiasis is frequently met with on the coast. Smallpox, dysentery and fevers, frequently of a bilious character, are endemic and occasionally epidemic. Cholera breaks out from time to time and works great havoc, as was the case in 1903 when one of the raja of Sarawak’s punitive expeditions was stricken while ascending the Limbang river by boat, and lost many hundreds of its numbers before the coast could be regained. Ophthalmia is common and sometimes will attack whole tribes. About one sixth of the native population of the interior, and a smaller proportion of those living on the coast, suffer from a kind of ringworm called kurap, which also prevails almost universally among the Sakai and Semang, the aboriginal hill tribes of the Malayan Peninsula. The disease is believed to be aggravated by chronic anaemia. Consumption is not uncommon.
Fauna.—The fauna of Borneo comprises a large variety of species, many of which are numerically of great importance. Among the quadrupeds the most remarkable is the orang-utan (Malay, ôrang ûtan, i.e. jungle man), as the huge ape, called mias or mâyas by the natives, is named by Europeans. Numerous species of monkey are found in Borneo, including the wahwah, a kind of gibbon, a creature far more human in appearance and habits than the orang-utan, and several Semnopitheci, such as the long-nosed ape and the golden-black or chrysomelas. The large-eyed Stenops tardigradus also deserves mention. The larger beasts of prey are not met with, and little check is therefore put on the natural fecundity of the graminivorous species. A small panther and the clouded tiger (so called)—Felis macroscelis—are the largest animals of the cat kind that occur in Borneo. The Bengal tiger is not found. The Malay or honey-bear is very common. The rhinoceros and the elephant both occur in the northern part of the island, though both are somewhat rare, and in this connexion it should be noted that the distribution of quadrupeds as between Borneo, Sumatra and the Malayan Peninsula is somewhat peculiar and seemingly somewhat capricious. Many quadrupeds, such as the honey-bear and the rhinoceros, are common to all, but while the tiger is common both in the Malayan Peninsula and in Sumatra, it does not occur in Borneo; the elephant, so common in the peninsula, and found in Borneo, is unknown in Sumatra; and the orang-utan, so plentiful in parts of Borneo and parts of Sumatra, has never been discovered in the Malay Peninsula. It has been suggested, but with very scant measure of probability, that the existence of elephants in Borneo, whose confinement to a single district is remarkable and unexplained, is due to importation; and the fact is on record that when Magellan’s ships visited Brunei in 1522 tame elephants were in use at the court of the sultan of Brunei. Wild oxen of the Sunda race, not to be in any way confounded with the Malayan seladang or gaur, are rare, but the whole country swarms with wild swine, and the babirusa, a pig with curious horn-like tusks, is not uncommon. Alligators are found in most of the rivers, and the gavial is less frequently met with. Three or four species of deer are common, including the mouse-deer, or plandok, an animal of remarkable grace and beauty, about the size of a hare but considerably less heavy. Squirrels, flying-squirrels, porcupines, civet-cats, rats, bats, flying-foxes and lizards are found in great variety; snakes of various kinds, from the boa-constrictor downward, are abundant, while the forests swarm with tree-leeches, and the marshes with horse-leeches and frogs. A remarkable flying-frog was discovered by Professor A.R. Wallace. Birds are somewhat rare in some quarters. The most important are eagles, kites, vultures, falcons, owls, horn-bills, cranes, pheasants (notably the argus, fire-back and peacock-pheasants), partridges, ravens, crows, parrots, pigeons, woodpeckers, doves, snipe, quail and swallows. Of most of these birds several varieties are met with. The Cypselus esculentus, or edible-nest swift, is very common, and the nests, which are built mostly in limestone caves, are esteemed the best in the archipelago. Mosquitoes and sand-flies are the chief insect pests, and in some districts are very troublesome. Several kinds of parasitic jungle ticks cause much annoyance to men and to beasts. There are also two kinds of ants, the sěmut âpi (“fire ant”) and the sěmut lâda (“pepper ant”), whose bites are peculiarly painful. Hornets, bees and wasps of many varieties abound. The honey and the wax of the wild bee are collected by the natives. Butterflies and moths are remarkable for their number, size, variety and beauty. Beetles are no less numerously represented, as is to be expected in a country so richly wooded as Borneo. The swamps and rivers, as well as the surrounding seas, swarm with fish. The siawan is a species of fish found in the rivers and valued for its spawn, which is salted. The natives are expert and ingenious fishermen. Turtles, trepang and pearl-shell are of some commercial importance.
The dog, the cat, the pig, the domestic fowl (which is not very obviously related to the bantam of the woods), the buffalo, a smaller breed than that met with in the Malayan Peninsula, and in some districts bullocks of the Brahmin breed and small horses, are the principal domestic animals. The character of the country and the nomadic habits of many of the natives of the interior, who rarely occupy their villages for more than a few years in succession, have not proved favourable to pastoral modes of life. The buffaloes are used not only in agriculture, but also as beasts of burden, as draught-animals and for the saddle. Horses, introduced by Europeans and owned only by the wealthier classes, are found in Banjermasin and in Sarawak. In British North Borneo, and especially in the district of Tempasuk on the north-west coast, Borneo ponies, bred originally, it is supposed, from the stock which is indigenous to the Sulu archipelago, are common.
Flora.—The flora of Borneo is very rich, the greater portion of the surface of the island being clothed in luxuriant vegetation. The king of the forest is the tapan, which, rising to a great height without fork or branch, culminates in a splendid dome of foliage. The official seats of some of the chiefs are constructed from the wood of this tree. Iron-wood, remarkable for the durability of its timber, is abundant; it is used by the natives for the pillars of their homes and forms an article of export, chiefly to Hong-Kong. It is rivalled in hardness by the kâyu těmběsu. In all, about sixty kinds of timber of marketable quality are furnished in more or less profusion, but the difficulty of extraction, even in the regions situated in close proximity to the large waterways, renders it improbable that the timber trade of Borneo will attain to any very great dimensions until other and easier sources of supply have become exhausted. Palm-trees are abundant in great variety, including the nîpah, which is much used for thatching, the cabbage, fan, sugar, coco and sago palms. The last two furnish large supplies of food to the natives, some copra is exported, and sago factories, mostly in the hands of Chinese, prepare sago for the Dutch and British markets. Gutta-percha (gětah pěrcha in the vernacular), camphor, cinnamon, cloves, nutmegs, gambir and betel, or areca-nuts, are all produced in the island; most of the tropical fruits flourish, including the much-admired but, to the uninitiated, most evil-smelling durian, a large fruit with an exceedingly strong outer covering composed of stout pyramidal spikes, which grows upon the branches of a tall tree and occasionally in falling inflicts considerable injuries upon passers-by. Yams, several kinds of sweet potatoes, melons, pumpkins, cucumbers, pineapples, bananas and mangosteens are cultivated, as also are a large number of other fruits. Rice is grown in irrigated lands near the rivers and in the swamps, and also in rude clearings in the interior; sugar-cane of superior quality in Sambas and Montrado; cotton, sometimes exported in small quantities, on the banks of the Negara, a tributary of the Barito; tobacco, used very largely now in the production of cigars, in various parts of northern Borneo; and tobacco for native consumption, which is of small commercial importance, is cultivated in most parts of the island. Indigo, coffee and pepper have been cultivated since 1855 in the western division of Dutch Borneo. Among the more beautiful of the flowering plants are rhododendrons, orchids and pitcher-plants—the latter reaching extraordinary development, especially in the northern districts about Kinabalu. Epiphytous plants are very common, many that are usually independent assuming here the parasitic character; the Vanda lowii, for example, grows on the lower branches of trees, and its strange pendent flower-stalks often hang down so as almost to reach the ground. Ferns are abundant, but not so varied as in Java.
Population.—The population of Borneo is not known with any approach to accuracy, but according to the political divisions of the island it is estimated as follows:—
| Dutch Borneo | 1,130,000 |
| British North Borneo | 200,000 |
| Sarawak | 500,000 |
| Brunei | 20,000 |
No effective census of the population has ever been taken, and vast areas in Dutch Borneo and in British North Borneo remain unexplored, and free from any practical authority or control. In Sarawak, owing to the high administrative genius of the first raja and his successor, the natives have been brought far more completely under control, but the raja has never found occasion to utilize the machinery of his government for the accurate enumeration of his subjects.