370 SMITH. 



THE COTABATO DISTRICT. 



The Cotabato district lies between that of Lanao and the Tiruray 

 Tablehmd. It receives its name from the town of Cotabato, which 

 is situated near the month of the Eio Grande. Physiographically it 

 is largely made up of bottom lands along the Eio Grande. A portion 

 of this bottom land is under water, a large area being covered by Lakes 

 Liguasan and Buluan. The moderately elevated hill country begins 

 on the slopes of the Kalintang Eange and extends south to the river. 

 The Eio Grande rises in the Subprovince of Bukidnon and flows south 

 in a tortuous course almost to Lake Liguasan. There it turns at right 

 angles and flows to' the west into Illana Bay. 



Little is known geologically about the country between the Kalintang 

 Mountains and the Cotabato Eiver. The United States Army engineers 

 have made an excellent topographic map of this region, which has been 

 incorporated in a large map of Mindanao published with this article. 

 On the trail between Parang and Cotabato I saw something of the 

 formation at the extreme western part of this district, and from an 

 examination of the topographic maps, and from what I saw at Fort Pikit, 

 about 160 kilometers to the east and in the center of this district, I 

 believe that the low hills to the north of the Eio Grande are largely 

 sedimentary: sandstones and shales capped with limestones. At Lake 

 Balut, a short distance south of Parang, I found sandstone and shale 

 beds varying in thickness from 30 centimeters to 1 meter, showing 

 sections of small anticlines and synclines; farther south in the hills 

 just north of the Cotabato Valley I encountered a section showing these 

 beds dipping towards the valley with a slight angle, and still farther 

 south some very much exposed gravel beds dipping 37° to the south. 

 The sandstone and shales with limestone capping, outcrop again in a 

 low hill at Eeina Eegente, and I once more met with these formations 

 at Pikit, which stands on another small hill. As it seems, the Valley 

 of the Cotabato is sjmclinal and not river-cut. I do not know how 

 these formations dip on the south side of the river, but should expect 

 them to incline to the north. I saw no igneous rock in this district, 

 save near Parang, in Muan Creek, where we hava the following section : 

 at the base, diorite with an undulatory surface; above this, shales and 

 sandstone in more or less thin beds; and above this, a sheet of basalt. 

 The trail runs for a short distance just south of Parang along the edge 

 of this lava flow, and black, carbonaceous shales, containing some fossils, 

 can be seen outcropping. Wlr ether or not there is coal below can only be 

 determined by sinking a shaft or by drilling. It seems that the southern 

 limit of the lava flow is at this point, as I found no more basalt in the 

 Cotabato District, nor more volcanic rock of any kind imtil we got 

 well up the Kabakan Eiver very close to the Matutan Eange, which is 

 the eastern boundary of the district. 



