104 B. KOTO : THE GEOLOGIC STEUCTUEE OF 



geologic structure, and I am under the impression, after reading 

 Posewitz's work, that even the axial chain does not fall into the 

 category of the folded mountain-range. 



Recently, quite a new aspect of the geologic structure of 

 Borneo has been opened by Molengraaff,'^'^^ who was one of mem- 

 bers of the Dutch Borneo expedition in 1893-'94. One of the 

 many discoveries he made is the existence of a chain of andesitic 

 volcanoes, called by him the Müller Mountains, along the south 

 side of the Kapuas river. Hitherto the rarity of neo-volcanic 

 rocks has been considered to be characteristic of this large island; 

 but as exploration has proceeded our former conception seems 

 likely to turn out to be erroneous. On the north of the Kapuas, 

 on the Sarawak frontier, there exists an east-west striking, folded 

 mountain range, consisting of slate, hornstone, and sandstone 

 (Palaeozoic?). This Upper Kapua range seems to keep its direc- 

 tion far into the Mahakkan river district in East Borneo (Kutai), 

 and the same holds true of the volcanic Müller chain and the 

 Schwaner ridge. The latter trending north-eastwards forms the 

 political and hydrographie boundary of the Kapua and Barito 

 basins, and belongs to the category of tilted mountain-ranges 

 with steep southerly cliffs, but sloping gradually to the north in 

 the plateau like upland of the Melawi basin. Such is a brief 

 account of Molengraaff's preliminary notice, differing greatly 

 from former notions as to this district. 



After all, we must confess that our data are too scarce to 

 give insight into the geologic structure. The late Neumayr''"^ 

 rightly asserted that Borneo's position in the Eastern Archipelago 



46) Petermanns Mlttheihirjen, Bd. 41, 1805, p. 203. 



47) ' Erdgescliicht ', Bd. II, 1887, p. 657. 



