8 FERGUSON. 



the land as it goes. Lehiiert '•' estimates for Borneo tliat under favorable 

 circumstances land may be thus formed at the rate of 100 meters in 

 forty to forty-five years. Near the mouth of the bay recent coral 

 largely replaces the mangroves as an agency for upbuilding the land. 



The movements of the western side of Port Barrera do not seem to 

 have been synchronous with those of the Aroroy district. Probably dur- 

 ing the greater part of the oscillations of the Aroroy region the opposite 

 side of the bay was submerged and its uplift seems to have taken place 

 contemporaneously with the depression of the opposite side. This in- 

 dependence of movement points to faulting along a line in the bay. 



LANANG TO IVIANDAON. 



Only a hurried reconnaissance was made southward from the Lauang 

 Mining Company's camp on the Lanang Eiver, and the country was 

 studied in far less detail than the Aroroy district. Leaving the amphi- 

 theater formed by the deserted meander of the Lanang, the ground rises 

 rather steeply to the south with hills composed of basalt, basaltic tufps 

 and conglomerate iintil Mount Nabongsuran is reached. This mountain 

 is the highest between Mounts Vil-lon and Mandaon, probably reaching 

 an elevation of over 300 meters, and has its long axis following the pre- 

 vailing northwesterly trend. The small, triangular valley of ilanda- 

 lidon is found at the foot of the mountain. The Mandalidon River 

 flows northwest to Port Barrera and a small branch Joins it here from 

 the northeast. The two hills to the west of Mount Nabongsaran, Mount 

 Masapinit and a smaller hill, both of conglomerate dipping to the 

 southwest, show the northeasterly trend which now becomes the dominant 

 feature of the country. 



The hills trend to the northwest for 6 or 7 kilometers southward from 

 the Mandalidon Biver. The Mabui Eiver, where it is crossed by the 

 trail, flows to the west, but soon turns and assumes a northwesterly 

 course, where it flows through a broad valley, on the southwestern side 

 of which a sharp escarpment of sedimentary rocks is encountered, show- 

 ing several prominent benches. This escarpment extends to Pagbulun- 

 gan Point, west of Mandaon, and is broken only by the two small canyons 

 of the Butuan and Mombog Creeks. For about 8 kilometers this line 

 of hills runs due south and then turns to the southwest for about 13 

 kilometers until it reaches Point Pagbulangan. jSTear this point it was 

 found to consist of conglomerate, shale, and sandstone, evidently of 

 marine rather than fluviatile origin, but in the northern part, as far as 

 could be judged at a distance, there was a capping of limestone as well. 

 This ridge forms the most prominent feature of the landscape of this 



"Lehnert: tjbef Landbilduiigen im Sunda-Gebiet, Deutsche)- Rundschau f. Geog. 

 u. Stat. (1882), 58. Quoted by Posewitz, Th., Borneo (English translation) 

 London (1892), 257. 



