RECONNAISSANCE OF MINDANAO AND SULU : III. 375 



work has already been published in the first part of The Eeconnaissance 

 of Mindanao and Sulu.' 



In this paper I shall add some translations by myself of the French 

 notes by Montano who was in the Philippines from 1879 to 1881. In 

 his report to the Minister of Public Instruction of France," Montano 

 paid some attention to the geology of Mindanao, as follows: 



All the facts which I have been able to observe in the interior and along the 

 coast of the eastern part of Mindanao tend to prove that this region has emerged 

 for the most part since the older epochs, or has imdergone in the Miocene epoch 

 an uplift which continues to this day. In following the course of the Sahug 

 River, one can not at first have any idea of the geologic constitution of the soil, 

 because in the lower reaches of the river there is a deposit covered with a thick 

 bed of humus. Higher up, the bed of the river is less deep and shows a number 

 of rapids formed by considerable blocks of rock. The rocks which constitute these 

 outcrops belong to several species, quartz porphyry, (porphyry petrosiliceux), 

 melaphyre and compact white and crystalline limestone. At 7° 40' north latitude, 

 that is to say, about 35 kilometers in a direct line from the Gulf of Davao, the 

 bed of the Sahug River is covered with enormous blocks of corals, which, according 

 to the section I secured belong to the genus Astroea, very much like species now 

 living in the Gulf of Davao. At several points where I could make out the 

 composition of the mountains, these are formed of calcareous terraces, which 

 appear to be horizontally stratified. In the center of Mindanao, Mount Hoagusan 

 separates the basin of the Sahug from that of the Agusan which empties into 

 Butuan Bay in the northern part of the island. Tubuan, an affluent of the Agu- 

 san, has its source on Mount Hoagusan at about 270 meters altitude. At this 

 point one finds melaphyres. The banks of the stream show some beds of plastic 

 clay with concordant stratification, dipping to the north at an angle of 45°. The 

 larger part of the stream bed is formed very extensively of calcareous terrane, 

 which at several points comes up in vertical masses from 20 to 40 meters in 

 height. Upon the right bank of the Agusan River north of Lake Dagun, or 

 Linao, about equally distant from the Gulf of Davao and Buluan Bay, is Mount 

 Banauan, the altitude of which is 240 meters above the level of the sea and 

 approximately 210 meters above the plain, which extends from its foot towards 

 the south. It seems entirely formed of andesite which occurs in blocks of from 10 

 to 20 cubic meters. This same rock, though altered, is found in the River Bana- 

 uan, which flows at the foot of the mountain. The andesites have been analyzed 

 by Monsieur Ch. Velain, Maitre de Conferences at the Sorbonne. 



The banks of the Agusan River from Mount Hoagusan to the sea are covered 

 with forest and hence still less is known of the nature of the rocks lying below. 

 Near the confluence of the Mahassan upon the right bank of the river, there is 

 a promontory of some meters elevation which is made up of beds of stratified 

 clay dipping 45° to the west. Between Las Myis and Butuan the left bank is 

 made up of altered diorite in peperin (tuff), stratified and dipping to the east 

 at an angle of 20°. 



The Agusan district, then, consists of two principal divisions: The 

 southern part, which is mountainous and in which the streams are swift 

 and full of rapids; and the northern, which is almost entirely plain, 



'' This Journal, Sec. A (1909), 3, 6. « Une Mission aux lies Philippines. 

 105046—2 



