Nov. 10, 1856.J WALLACE ON BORNEO. 201 



or Pontianak River. The Linga Eiver, the first branch of the 

 Batanglupar from the south, flows through a flat and swampy 

 country almost from its source, near the Klingkang Mountain ; and 

 the passage from the higher part of the Batanglupar to the great 

 lakes of the Upper Kapuas, is described as being over a scarcely 

 elevated, certainly not a mountainous country. I am inclined, 

 therefore, to believe that the little mountain district, from which 

 flow the Sarawak and Sadong Eivers on the north, and the Sikyam 

 and Landak on the south side, forms the central nucleus of the 

 north-western end of Borneo. These rivers, in their upper part, 

 are true mountain streams, flowing swiftly over gi'avelly beds, or 

 rushing over rocky ledges, and forming so many little rapids and 

 falls, that we cannot put their descent at less than 25 to 30 feet a- 

 mile, probably much more. Now, on the Sadong, more than 30 

 miles of the river has this character, while 20 more is a deep and 

 swift-flowing stream. This would give an elevation of a thousand 

 feet for the base of this mountain region, showing that it differs 

 essentially in character from those mountains nearer the coast, 

 which, though of equal elevation, rise abruptly from a flat and 

 marshy country which is scarcely elevated above the level of the 

 high tides. 



Geology. — The geology of the country is exceedingly difficult 

 to elucidate, owing to its great complication, to the difficulty of 

 obtaining sections, and the excessive rarity of organic remains. Tn 

 no case have I been able to ascertain, by direct observation, the 

 order of superposition of any of the formations. The most extensive 

 formation in the country is a ferruginous sandstone conglomerate. 

 This composes most of the mountains near the coast, and also the 

 whole of the central mountain region. Between these and often in 

 contact with them, occur limestone and porphyritic or trappean 

 rocks, and a hard slaty rock, which is sometimes highly crystalline. 

 The sandstone rocks are generally inclined at an angle of from 7 to 

 20 degrees with the horizon, while the slaty rocks are always nearly 

 vertical. No distinct stratification is observable in the limestone, 

 which forms abrupt and fantastically formed isolated mountains, often 

 presenting mural precipices of much grandeur, and it is in these that 

 the hirundo esculenta forms the gelatinous nests, which are so great 

 an article of luxury with the Chinese. On my sketch-map* the 

 dip and direction of the strata are noted, wherever I observed them. 

 It is in the sandstone and the clayey beds which alternate with it, 

 that the coal occurs, and there seems little reason to doubt that it is of 



* In the Map-room of the Society. — Ed. 



