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Reprinted from " NATURAL SCIENCE" for April, 1892. 
 
 The 
 
 Physical Features and 
 Geology of Borneo. 
 
 BY 
 
 F. H. HATCH, Ph.D., F.G.S. 
 
The Physical Features and Geology of Borneo. 1 
 
 FROM the day when the companions of the ill-fated Magellan cast 
 anchor before Brunei, in the early part of the sixteenth century, 
 down to the present time, the island of Borneo has ever provoked a 
 lively curiosity, and has been the subject of the wildest speculation. 
 Its vast size and symmetrical position on the equatorial line early 
 attracted the attention of geographers ; but the exploration of the 
 interior was long hindered by the trade policy of its first settlers, the 
 Dutch East India Company, who deemed it expedient to confine their 
 operations to the coast. 
 
 In more recent years, the popular imagination has been kindled 
 by the romantic history of Sir James Brooke. That daring English- 
 man, arriving off the northern coast of Borneo, partly in search of 
 adventure, partly with the idea of suppressing the Malay pirates who 
 infested those seas, found himself, at the end of a few exciting years, 
 installed as Rajah of Sarawak and ruler of a turbulent crowd of 
 Malays, Dyaks, and Chinese. Strange rumours have also reached 
 us of the ferocity of the head-hunting and cannibal tribes who share 
 the forests of the interior with the orang-outang. 2 Lastly, the enter- 
 prise of the capitalist and the energies of the prospector have been 
 stimulated by exaggerated reports of the wealth of the island in 
 minerals and coal, of its wide-spreading gold-fields, and of its diamonds 
 of fabulous size and unparalleled lustre. And yet, in spite of these 
 manifold sources of interest, there is hardly another country of equal 
 magnitude of which we know so little. It is true that the naturalist 
 Wallace, in his " Malay Archipelago," draws a charming picture of 
 the life and vegetation of the dense tropical forests of the island ; but of 
 its physical features we have, till recently, been in complete ignorance. 
 
 The vacuity of our knowledge of Borneo appears the more 
 remarkable when we contrast it with the exactitude and minuteness of 
 our information with regard to the neighbouring islands of Sumatra 
 and Java ; but the explanation is not far to seek. This is embraced in 
 
 1 For the facts on which this essay is based, I have mainly relied on Dr. Theodor 
 Posewitz's " Borneo " (Berlin : Friedlander und Sohn, 1889). I have recently trans- 
 lated this invaluable work, in which the whole of the literature (principally Dutch) 
 has been admirably summarised ; and it is with considerable satisfaction that I am 
 able to announce the approaching publication of the English edition. — F. H. 11. 
 
 8 See Carl Bock's " Head-hunters of Borneo.'' London : 1881. 
 
 411645 
 
. . . #; ... ....... . . t •'% io 9 
 
 the physical and political conditions of the countries. The attenuated 
 shape of Sumatra and Java makes it impossible to travel to any 
 considerable distance from the coast ; and they have been for many 
 years under European rule. The configuration of Borneo is quite 
 different. Its compact and rounded form measures 675 geographical 
 miles, both from north to south and from east to west ; while only 
 the margin of its enormous area (219,034 square geographical miles) 
 
 ft' 
 
 Map of Borneo. 
 
 has been brought under the complete dominion of the Dutch and 
 English. 
 
 The island has been traversed from coast to coast on more than 
 one occasion by intrepid travellers, who, following one or other of 
 the great rivers to its source, crossed the dividing range into the 
 basin of another stream, which ultimately led them to the coast. But 
 the main portion of the interior has remained, and, to a large extent, 
 still is a terra incognita. The difficulties of transport through impene • 
 trable forests, and over high mountain ranges, and the dangers to be 
 apprehended from the hostility of the native tribes, have combined to 
 
IlO 
 
 deter the scientific investigator from venturing far into the unknown 
 and inhospitable regions of the interior. 
 
 In those districts where European settlements have long existed, 
 for instance, in the districts of Bandjermassin and Tanah Laut in 
 the south-eastern portion of the island, more exact details respecting 
 its physical and geological structure have been obtained, for in these 
 districts the country has been carefully examined in the eager search 
 for useful minerals. 
 
 Much of the knowledge thus accumulated in the Dutch part of 
 the island is due to the labours of the Natural History Commission, 
 a scientific institution established in Batavia in the year 1820. Its 
 members were scientific men, comprising, in the first instance, a 
 zoologist, a botanist, and a geologist; and they were appointed for the 
 purpose of investigating the resources of the as yet almost unknown 
 island. At a later period, the geology of some portions of the island 
 was elucidated by the work of the Batavian mining engineers, who 
 were sent by the Dutch Government to search for useful minerals 
 and for coal. 
 
 On the northern coast, our knowledge has received its greatest 
 increment in Sarawak, by explorations carried on at the instigation 
 of Rajah Brooke and his successor, Charles Johnson Brooke, and in 
 Sabah, where the British rule has been inaugurated by the exertions 
 of the North Borneo Company. Since 1881, when the company 
 acquired its charter, our geographical and geological information of 
 this part of the island has increased with every year. A band of 
 courageous pioneers and explorers, defying every danger, have 
 traversed these unknown regions in all directions, and scientific 
 results of great value have been thus obtained. 
 
 Physical Features. 
 
 Proceeding from an elevated area in the centre, the radiating 
 lines of water-parting divide the island into a southern, a northern, 
 a western, and an eastern catchment basin. The divides, however, 
 are not, as usually represented on the maps, formed by continuous 
 mountain chains, but consist of a series of short ranges and abrupt 
 ridges, or of isolated groups of mountains and single peaks, which are 
 turned in the same general direction. Surrounding the mountains 
 is a low undulating country in which the separate and outlying 
 masses lie like islands in a sea. 
 
 This structure is the dominant feature of the orographic systems 
 of Borneo, and is cleverly epitomised by Posewitz when he names 
 the detached portions of the high land "mountain-islands." The 
 gently rolling country which laps round the foot of the " mountain- 
 land " he describes as " hill-land." The hill-land, in its turn, is 
 bordered by dry plains which are often of great extent, especially 
 in South Borneo; and these, again, pass into the swamps and 
 morasses of the coast. Like the mountain-land, the hill-land sends 
 
Ill 
 
 out spurs into the plains, and tongues of the latter extend into the 
 marshes. 
 
 According to Schwaner, the central mountain tract has a north- 
 east and south-west strike, and culminates in two high peaks — the 
 Gunong Tebang and Gunong Apo Borau, estimated at from 5,000 
 to 6,000 feet high. The four chief ranges that branch off from this 
 massif extend towards the south-east, south-west, north-west and 
 north-east, and constitute the chief political boundaries. 
 
 The south-eastern chain has a varied character. Its central 
 portion consists principally of hill-land through which only isolated 
 peaks (mountain-islands) project; but its northern and southern 
 parts are more ruggedly developed, and steep ridges and rocky peaks 
 rise to a considerable height. The southern limit of this chain is 
 formed (in Tanah Laut) by the Meratus mountains, the highest peak 
 of which is 4,250 feet above the sea-level. 
 
 The south-western chain extends from the central tract to near 
 Cape Sambar, which is the extreme south-western point of the island. 
 With the exception of a few hilly tracts in its central part, this chain 
 retains throughout a rugged Alpine character. Its highest point is 
 reached in the Rajah Bukit — the Olympus of the Dyaks — which is a 
 peak of 7,000 to 8,000 feet. Schwaner describes a portion of the 
 chain as consisting of a high plateau, 20 to 30 miles wide, the surface 
 of which is broken by numerous dispersed peaks. 
 
 The northern chain, which comprises a north-eastern and a 
 north-western branch, is less known than the southern chains. Its 
 highest part is reached at its northern limit in the imposing massif 'of 
 Kina-balu (13,698 feet) ; in its middle portion the peaks vary from 
 6,000 to 8,000 feet, and still further west, between Sarawak and West 
 Borneo, they decrease to 2,000 — 3,000 feet. The western branch of 
 the chain terminates in the Datu Mountains, spurs of which reach the 
 sea, forming the promontories of Api and Datu. Isolated peaks of 
 this part of the chain have an altitude of 6,000 feet. 
 
 In their general character, the northern chains are similar to the 
 south-western chain, being composed of detached ridges and moun- 
 tain-islands. Kina-balu is the highest mountain in Borneo, and is 
 held in much veneration by the natives. This fine mass is situated 
 in the territory of the British North Borneo Company, and forms a 
 striking feature in the scenery of this part of Borneo. It consists of 
 about ten peaks in a line, running east and west, while a solitary 
 peak rises on the south, separated from the others by a deep and wide 
 ravine. Several of its peaks have been ascended by English 
 explorers. Spenser St. John describes the view from one of the 
 summits as magnificent : the coast-line of North Borneo is visible as 
 far as the island of Labuan, while to the south and south-east the eye 
 ranges over a multitude of ridges and peaks of from 7,000 to 8,000 
 feet. 
 
 In the central mountains rise all the principal rivers — the 
 
112 
 
 Barito, which flows towards the south, the Kapuas to the west, the 
 Rejang to the north, and the Mahakkam to the east. The Barito is 
 570 miles long, according to Schwaner. Besides these large rivers, 
 there is a great number of smaller streams, which rise in the 
 different mountain chains. , 
 
 The rivers of Borneo pass through three distinct phases in 
 their passage from the mountains to the sea. In an upper course they 
 rush over a rocky bed with cataracts and rapidly shifting pebble 
 islands. The middle course is through a more level country, in which 
 the stream is often replaced by a string of lakes. The extent of these 
 lakes depends on the time of year ; during the rainy season the 
 surrounding forests are often flooded for miles, while in the dry season 
 they partially dry up, leaving a black fertile land, dotted with small 
 patches of water. Such, for instance, is the case in the rivers 
 Barito and Kapuas, both of which have an extended lake district. 
 Another feature of this part of the course is the formation of natural 
 canals (antassan) which cut across the loops. Similar natural canals 
 (trussan) connect neighbouring rivers with one another. They are 
 formed by the floods that arise during the west monsoon, and are 
 very serviceable as water-routes to the traveller. 
 
 In the lower course, the river winds slowly through a flat swampy 
 country, fringed with mangroves, nipa-palms, and other tangled jungle 
 growth. This lagoon district is inundated daily at high water, and 
 is covered for months during the rains. On retreating, the subsiding 
 waters leave behind a black mud, rich in humus and full of shells. 
 A large amount of this mud is brought down by the rivers. Its 
 accumulation causes the formation of numerous mud islands. Occa- 
 sionally the accumulation takes place in such a manner as to form a 
 natural embankment, through which the river flows at a higher level 
 than the surrounding marsh-land. A part of the sediment is carried 
 out to sea, where it is deposited in banks which often constitute 
 dangerous bars across the mouths of the rivers. On the east coast 
 there are mud banks extending for 8 — 10 nautical miles into the sea; 
 even at a distance of 10 miles the sounding line only gives a depth 
 of 33 feet. 
 
 The deposition of sedimentary material brought down by the 
 rivers, protected in some cases by the presence of coral-reefs, causes 
 a rapid extension of the coast. This is aided by the growth of the 
 jungle vegetation. On the newly-formed marsh-land mangroves soon 
 spring up, and by their pendant air-roots favour the accumulation of 
 the mud. The forward movement of the mangrove woods has been 
 estimated to amount to be more than a hundred metres in forty years. 
 Another jungle tree which acts in a similar manner is the nipa- 
 palm. Flourishing alike in salt or fresh water, its matted roots serve 
 admirably to retain the flotsam of the rivers ; and it is propagated 
 rapidly by its angular fruit, which, on falling, sinks easily into the soft 
 mud. On the coast of Sarawak the annual increase is estimated at 
 
H3 
 
 15 — 18 feet. The formation of new land is further aided in South 
 Borneo (Tanah Laut) by the deposition of the fine mud brought 
 down by the river flowing through the gold-washing districts. 
 
 . Geology. 
 
 Posewitz treats the geology of the island under four principal 
 heads: — (i) The mountain-land; (2) the Tertiary hill-land ; (3) the 
 diluvium, or drift of the plains ; (4) the alluvium of the marshes. 
 
 The mountain-land consists partly of crystalline schists, with 
 which old eruptive rocks (granites, diorites, gabbros, and serpentines) 
 are associated, partly of a slate-formation which appears to be of 
 Devonian age. So little is known of the geology of the mountain- 
 land, that the schists have not been separated from the slates, and 
 even the Devonian age of the latter is only problematical. The 
 slate-formation comprises phyllites, sandstones, conglomerates, and 
 quartzites. The Devonian (?) rocks are in places overlain by a 
 Carboniferous formation consisting of a hard bluish limestone (Car- 
 boniferous Limestones), succeeded by coarse white sandstones. This 
 Carboniferous formation is largely developed in North Borneo, where 
 it appears to extend from Sarawak to the Bay of Marudu. It has 
 not been separated from the underlying slates, but is clearly marked 
 off from the Tertiary beds that succeed it. 
 
 The presence of Cretaceous rocks in Borneo has been proved 
 by the discovery by Van Schelle, in West Borneo, of ' fossils which 
 have been referred by Geinitz to the Upper Chalk. This is the first 
 recognition of the presence of Mesozoic rocks in the Indian Archi- 
 pelago. How far they extend is at present unknown, but recent 
 researches of Martin* appear to show that rocks of this age have a 
 wide range in Borneo. 
 
 The Tertiary hill-land forms a broad belt round the mountain- 
 land. It consists of a gently rolling country, which near the mountain 
 border rises into hills of 200 — 300 feet (Eocene), but elsewhere dies 
 away into the common level of the plains (Miocene). 
 
 Verbeek divides the Eocene of Borneo into three stages, 
 namely : a, the sandstone stage ; /3, the marl stage ; and v, the lime- 
 stone stage. 
 
 The sandstone stage (a) is the lowest, and, from a practical point 
 of view, the most important, since it contains the Borneo black coal. 
 It consists of alternating beds of sandstone shales, carbonaceous 
 shales, and coal-seams. 
 
 The marl stage (0) comprises shales and marls, some of which 
 are very fossiliferous, containing numerous remains of Crustaceans. 
 One whitish-grey bed of marly limestone is packed with Orbitoides 
 and Nummulites. 
 
 3 Tenison Woods has described the following fossils, derived from this forma- 
 tion in Sarawak : a Vertebraria, Phyllotheca australis, a Fenestella, and a Stenopora. 
 
 i See Nature, 1889, p. 121. 
 
ii 4 
 
 The limestone stage (7) consists of a hard white or bluish lime- 
 stone, containing numerous fossils (Corals, Sea-urchins, Lamelli- 
 branchs, Gasteropods, Orbitoides and Nummulites). This stage 
 appears to be the equivalent of the Nummulitic Limestone of 
 Europe. 
 
 Schwaner describes it in the following terms : " The limestones 
 possess the undoubted characteristics of a littoral formation : they 
 consist of enormous aggregates of coral and broken shells, inter- 
 mingled with the spines of echinoderms ; and resting on a bed of hard 
 rock, they follow the boundaries of the high ground, into its bay-like 
 inlets and round its projecting promontories." 
 
 Space does not permit me to give details as to the development 
 and distribution of these important Eocene deposits, nor to describe 
 their fauua and flora.s Suffice it to say that stage a has been found 
 to reach a thickness of 524 feet ; stage $, to 820 feet ; and 
 stage 7. to 295 feet. With regard to the fauna, eighteen species of 
 Gasteropods have been determined, all of which are marine types. 
 They indicate a tropical climate, the majority of the species having 
 their nearest representatives in the present fauna of the Indian 
 Archipelago. The Lamellibranchs are better represented than the 
 Gasteropods, and comprise an abundance of characteristic marine 
 forms, indicating both deep and shallow seas. The Nummulites 
 belong to four different species, two of which are peculiar to Borneo 
 (N. ptngarontnsis, Verb.; N. sub-brongniarti, Verb.; N. biaritzensis, 
 d'Arch.; N. striata, d'Orb. var.). The coral fauna of the Nummulite 
 beds consist of species peculiar to Borneo (belonging to the Turbino- 
 lidae, Stylophorinae, Astraeidae, Madreporidae, and the Poritidae) and 
 are of a reef-forming type. The flora has an Indian character, 
 showing a remarkable resemblance to types now living in the East 
 Indies. 6 
 
 The Eocene strata have been pierced in numerous places by 
 the eruption of andesitic lavas. These lavas are bedded, and are 
 accompanied by tuffs. Since they have broken through the highest 
 beds of the limestone stage, they are probably of Miocene age. 
 Above the andesites lies a series of shales and sandstones, which 
 Verbeek describes as Late Tertiary (Miocene). The lower beds 
 consist of soft shales and harder marls. The greenish sandstones 
 which lie above them have, in great measure, derived their material 
 from the andesites and tuff. These Miocene beds contain occasional 
 seams of brown coal, which is very inferior^ as fuel to the black coal 
 of the Eocene beds. 
 
 * An admirable summary, with full reference to the literature, will be found 
 in Posewitz's "Borneo." 
 
 • "The vegetation of the Sunda Islands has retained its Indian character, from 
 the Eocene period down to the present time, although the Tertiary floras of Europe 
 have been considerably modified." Geyler, Jaarb. v. h. Mynwezen in Ncderl.-Ind. 
 1879. II. 
 
"5 
 
 The diluvium (drift) of the plains occurs chiefly as a zone 
 round the Tertiary hill-land, though it also covers the flanks of the 
 mountains. It is of great practical importance, as it contains the 
 chief deposits of gold, platinum, and diamonds. It may be described 
 as solid flat land in contradistinction to the marsh-, hill-, and mountain- 
 land. Its composition is fairly uniform, its upper part consisting of 
 clays and sandy clays, its lower of pebble beds. It is between the 
 pebbles of the latter that the precious metals and stones are found, 
 mixed with a fine clayey earth. In some places the pebbles are 
 united by a siliceous cement to a hard conglomerate. 
 
 The alluvium of the marshes has a wide distribution in Borneo. 
 Its mode of occurrence has been already referred to. The marsh- 
 land rises very slowly from the coast. This is shown in the lower 
 course of the rivers by the great distance from the mouth at which 
 the influence of the tides is still perceptible. The Barito, for instance, 
 is tidal for fifteen geographical . miles, while in certain seasons the 
 influence of the tides may be observed at a distance of thirty-five 
 geographical miles. It is also shown by the immense area covered 
 by the diurnal and periodic floods. The area flooded daily in the 
 basin of the Barito is estimated by Schwaner at 160 square geo- 
 graphical miles, or one-twelfth of the whole river-basin, to which 
 420 square miles must be added in the rainy season. Consequently, 
 during the west monsoon, 580 square geographical miles, or more 
 than one-third of the river basin, are under water. 
 
 With regard to the geological evolution of Borneo, Posewitz's 
 ideas are not altogether in unison with those that have been expressed 
 by Wallace in respect to the whole of the Malay Archipelago. While 
 Wallace regards these islands as having been produced by the break- 
 ing up of a continental area, Posewitz describes Borneo as resulting 
 from the fusion of an archipelago of small islands. The grouping of 
 the different island-clusters in this archipelago has been preserved in 
 the main features of the present structure. A narrow island, which 
 extended from north-east to south-west, is now the Tanah Laut 
 range. Parallel to it was the mountainous island of Pulu Laut. The 
 Pramassan Alai and Amandit mountains were represented by islands 
 of the same general type. To the north there extended a broad sea, 
 lapping round the foot of the central mountains. A few peaks rose 
 from its surface, marking the direction of the south-east mountain 
 chain. In the south-west was a large cluster of small islands, which 
 are now the mountains of Sukadana and South- West Borneo. A 
 large island occupied the position of the present Chinese districts, 
 and from it a chain of islands extended to the great mass of Kina-balu 
 in the north-east point of Borneo. 
 
 In the beginning of the Tertiary period the seas surrounding 
 these islands began to be filled in by the deposition of sedimentary 
 matter. Borneo now acquired a shape resembling that of the neigh- 
 bouring island of Celebes. Great gulfs and armi of the sea, fringed 
 
n6 
 
 by coral reefs, occupied the place of the low-lying plains of the 
 Borneo of to-day. 
 
 At the close of the Tertiary period, the gulfs gave way slowly to 
 dry land ; the seas became shallower and retreated, thus preparing 
 the way for the advent of the present period. Numerous and powerful 
 streams carved out a passage from the mountains and flowed towards 
 the retiring seas, bringing with them their quota of mud and fine sand 
 with which to increase the extent of the growing island. Thenceforth, 
 down to the present time, no important changes have modified the 
 physical features of Borneo ; and the island has enjoyed a remarkable 
 immunity from the fierce paroxysms of volcanic activity that, during 
 the Recent period, have convulsed the other large islands of the 
 Malay Archipelago, and culminated, in the year 1883, in the 
 extraordinary outburst of Krakatoa. 
 
 F. H. Hatch. 
 
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