GEOLOGIC RECONNAISSANCE OP MINDANAO AND SULU. 493 



FROil COTABATO TO DAVAO. 



The town of Cotabato is situated on tlie south bank of the novtli 

 branch of the Rio Grande de Mindanao. It consists of a collection of 

 low, white, Spanish houses fairly close together, with the usual native 

 huts straggling about in the environs. Just soutli of and on the edge 

 of the town is a limestone hill about 150 meters high from whicli a 

 magnificent panorama (Plates XVI and XVII) can be olitained of 

 the surrounding country. This hill is an outpost of a greater mass 

 which is to be found to the south, and which formerly was undoulit- 

 edly still more extensive; it is very remarkable in that it stands out in 

 the middle of the great delta, which forms all the river plain from the 

 mouth of the river back and even beyond Fort Pikit. 



The most notable feature of the topography of this plain, beside the 

 hill just mentioned, is the old terrace lines which swing along, but not 

 always parallel to, either side of the river. These terraces are undoubtedly 

 of marine origin, for close to Cotabato they are seen to be raised coral- 

 reef shelves with the characteristic steep seaward slope of such formations. 

 The evidence seems quite sufficient, to me at least, to supjDOse that 

 the sea once swept far up this intermontane region which is now so filled 

 with sediment. Indeed, I am convinced that it one time extended through 

 to the Gulf of Davao, for in the stretch between the Pulangui Ei-^-er and 

 Davao there are very recent sediments and volcanics which have closed 

 up the passage. 



Cotabato hill is composed of a cavernous limestone with a fair sprink- 

 ling of fossils, corals, gasteropods, lamellibranchs, etc., all of compara- 

 tively recent age, presumably Miocene, although no specific determinations 

 have as yet been made. 



Plate XVIII shows the interior of a native salt-making establishment at the 

 lo\\'er end of the delta. Sea water is sprayed over glowing embers, the salt is 

 precipitated and afterwards washed oS and run through the large filter shown in 

 the background of the picture. This filter contains wood ashes and earth. At 

 the Moro foundry near Cotabato, bolos, krises, and many metal boxes of brass and 

 silver are fashioned. 



After some delay, we set out for Datu Piang's place at Cuderangan, 

 some 50 Irilometers above Cotabato. Here we learned from Lieutenant 

 Younglof, Philippine Scouts, of oil seeping from the river bank about 

 half way between Eeina Eegente and Fort Pikit and also near Pikit of 

 a blue, plastic, oily clay which burns to a white color and is quite re- 

 fractor)^. The Moros are said to come great distances to obtain this 

 material. 



Eeina Eegente is on a hill of limestone similar to that of Cotabato. 

 It is a monadnock. The underlying foundation is sandstone which will 

 doubtless he found to be a good water carrier; it is very probable that 

 good conditions for artesian wells can be obtained at almost any point 

 of the valley. 



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