GEOLOGIC EECOXNAISSANOK OF MINDANAO AND SULU. 477 



its nine or ten lakes and its high mountains. One of the latter. Mount 

 Apo, 2,928 meters, is supposed to be the highest peak in the Archipelago 



A glance at the map of Mindanao prepared by the Jesuits "will reveal 

 the presence of four main tectonic lines, three of which run approximately 

 north and south, and the fourth east and west. The first is the line 

 following the crest of the range which extends jJai'allel to the long axis 

 of the Zamboanga Peninsula; its direction is I^. 20° E. The second 

 seems most nearly to mark the eastward trend of this range; its direction 

 is approximately ^. 85° W. Along this line are to be found Mount 

 Sugarloaf, just north of Dumankilis Bay, Mount Dapan, a short distance 

 southwest of Lake Lanao, Mounts Kalatungan and Latukan east of the 

 lake, and Mount Agtunganon east of the Agusan Eiver. 



The next line is that which follows the Apo Eange. This is very 

 pronounced from Apo southward, but is not especially marked to the 

 north. On this line are to be found Mount Apo, 2,928 meters, and Mount 

 Matutun, which is doubtless somewhat lower. 



The fourth, which is not as straight as the others, extends along the 

 backbone of the country east of the Agusan Eiver; its general direction 

 is about K. 8° "W". No very important peaks exist along its extent. 



The first of these four lines, which -follows the backbone of the Zam- 

 boanga Peninsula, is the most marked in that it extends northward 

 through the Island of ISTegros, coinciding exactly with the tectonic ILae 

 of that island and cuts across the lower part of the prong of Masbate, 

 again coinciding with the long axis of Sorsogon and the Catanduanes. 

 The Agusan line, by curving a little to the west, would fit closely with 

 the tectonic lines of Leyte, Masbate, and Tayabas. There is no question 

 but that there is a definite and fairly uniform system of folding and 

 fracturing tlirougliout the Archiijolago, tlie various islands representing 

 the irregular crests of the anticlines while the intervening straits mark 

 the synclines. 



There are no \erj large rivers in the western part of Mindanao, 

 although a fair-sized river follows along the central line of the Zam- 

 boanga Peninsula, and two short, swift streams also exist, one of them, 

 the Agus, draining Lake Lanao and emj)tying into Iligan Bay after a 

 run of about 30 kilometers, and the other, the Mataling Eiver, drawing 

 part of its water from Dapan Lake and part from the northern slopes of 

 the Kulingtan Eange. A difl^erent condition exists in other parts of 

 Mindanao. 



The Rio Grande cle Mindanao, over 300 kilometers long, is the second 

 largest river in the Philippine Archipelago. Its course is from north to 

 south until within a short distance of Lake Liguasan where it turns 

 sharply to the west, emptying into Illana Bay. Tliis river is navigable 



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