THE MALAYAN ARCHIPELAGO. 107 



Kamiongan (Mangkalihat) in Borneo, turns at first north-east, 

 and then due east, with the tectonic basin of the Gulf of Tomini 

 in the inner (south) side of the mountain-curve. P. and F. 

 Sarasin''^^ crossed between Buol and Marisa in the western tract 

 of the northern arm of Celebes, and found old eruptives and 

 thick, red (Tertiär}- ?) clay in the interior, with modern coral 

 reefs on the shore, })ut not a trace of neo-volcanic effusives 

 The same explorers made another overland journey between 

 Amurang and Gorontalo, across the northern peninsula, and 

 made known the existence of a meridional tectonic line throusfh 

 Bolang and Malibaga. The westerly region lying between this 

 line and the before-mentioned Buol-Marisa area is occupied 

 by a granitic nucleus with a mantle of gneiss and shale, the 

 latter being overlaid by Pliocene conglomerate,^"^ which is made 

 up of gravels of shale and basaltic materials. The coast is every- 

 where fringed with recent coral reefs. An equatorial trench 

 fault runs along the south coast and the Lake of Limbotto 

 near Gorontalo is the deepest point of this bicataclase depres- 

 sion between the granitic ' horsts.'"^^ 



Along the before-mentioned tectonic line'^*^ through Bolang 

 and Malibaga, the peninsular area, including Minahassa, Bolang 

 and Mongondo has been depressed, and upon that sunken socle 

 of conglomerate and Orbiioides-limestone^^^ are heaj^ed up several 

 volcanic rocks, by which this portion of the island is charac- 

 terised. The volcanic line traversing the portion in question 

 represents only the prolongation of a great earth-fissure, which 



51), 52) Zeitschr. d. Gesell, f. Erdkunde, z. Berlin, Bd. 29, 1S94. 



53) Wichmann, Pefermanns Mitteilwujen, 1893, S. 9. 



54) P. u. F. Sai-asin, loc. cit. (46). 



55) Martin. Beiträge zur Geologie OstcLsiens, etc., Bd. Ill, p. 581. 



