Reviews— Dr. Molengraaff' s Central Borneo. 17! 



The coal-seams in these Tertiary beds appear to be formed of 

 plant debris and trees brought down by the river floods, and not of 

 slowly formed vegetable growths in situ, as is the case with most 

 Palgeozoic coal-seams. As a rule, the Borneo coal is too much mixed 

 up with sand and clay to be of economic value, but the author records 

 several localities where the beds are of sufficient purity and thickness 

 to be worth prospecting for mining purposes. They are shown on 

 the north shore of the Kenepai river (p. 38) ; on the Mondai river 

 (p. 60 ; also Atlas, Map 6, sect. F & H) ; below Karangan Pandjang 

 (p. 273) ; on the Sekilit, a tributary of the Tebaoeng, several layers 

 of fairly good but somewhat fissile coal were exposed (profile B, 

 Map ixa, pp. 288 and 293) ; and again on the Pinoh river, where 

 a bed of coal of inferior quality rests on claystone beds with 

 concretions and numerous shells (see section p. 142, fig. 35). 



Succeeding the Old Tertiary Sandstone formation, there ar& 

 extensive deposits of fluviatile and lacustrine origin, consisting of 

 beds of fine sand and mud mingled with vegetable debris, which are 

 regarded as probably of Quatei-uary age ; but in Borneo there is such 

 a close resemblance in the sandstones and clays of difi'erent ages that 

 in the absence of fossils it is almost impossible to determine between' 

 those of Tertiarjs Quaternary, and recent dates. 



Owing to the heavy tropical rainfall, the denudation of the higher 

 land-areas in Borneo is on an enormous scale, and the gravels, sands, 

 and finer materials brought down by the rivers are spread over 

 extensive areas. Thus in West Borneo, which has a total area of 

 145,000 square kilometres, it is estimated that 30,000, or nearly 

 one-fifth, are covered deeply with alluvial deposits. 



Between the hills and the flat alluvial grounds of most of the 

 large rivers, there are older fluviatile deposits of a gravelly character, 

 which generally contain gold. The gold is obtained by Chinese,- 

 who work the beds in a very primitive manner. They are very 

 reticent respecting the results of their operations, which are probably 

 not over remunerative, but if hydraulic machinery were employed 

 the chances of success would be greater. 



All the later changes in Borneo appear to be due to atmospheric 

 influences, which have greatly diminished the height of the island, 

 and at the same time enlarged its circumference by the rapid 

 deposition of the alluvial material brought down by the rivers. 

 The finer materials are carried far out to sea, and, from the dis- 

 coloration of the water round the coasts, Borneo has received its- 

 name of " Mudland." 



Intrusive and eruptive rocks are largely developed in Central 

 and South Borneo. Granite areas occur in the Schwaner mountains, 

 the base of which principally consists of this rock, and in the 

 bordering hilly districts of South Borneo ; also in the Semitau Hills,, 

 the Boengan Hills, and the lake district. It is mainly an amphibole- 

 biotite-granite with plagioclase, which frequently passes into tonalite. 

 Its intrusive character is proved by the intense alteration of the 

 surrounding rocks near the zone of contact. 



Diorite, gabbro, norite, peridotite, serpentine, and diabase have 

 been met with in different districts. 



