232 The Philippine Journal of Science lais 



River, which flows north into Iligan Bay over a distance of 24 

 kilometers. Agus River is swift-flowing and forms an important 

 cascade in Maria Christina Falls, where the water makes an 

 uninterrrupted plunge through a vertical distance of 58 meters. 

 No large stream flows into the lake. 



Lake Lanao is a center of Moro population. Two American 

 military posts are located on its shores, and there is considerable 

 traffic across it. The Spanish Government maintained a small 

 gunboat on Lake Lanao as a part of the military operations 

 against the Moros. 



Smith ^^ believes that Lake Lanao was formed by the damming 

 of a basin between two mountain ranges, by flows of lava, and 

 by accumulations of wash. The lake shores rise abruptly on 

 the south, but on the north there is only a gentle upward slope 

 for some distance from the water's edge, followed by an abrupt 

 drop of 50 meters or more to the north, making a terrace which 

 Smith designated as the Keithley escarpment. 



LAKE MAINIT 



Lake Mainit, on Surigao Peninsula in northern Mindanao, is 

 a fresh-water lake, roughly circular in outline, that covers an 

 area of about 75 square kilometers. Montano estimated that its 

 surface stood 40 meters above sea level; and Father Francisco 

 de P. Sanchez, a Jesuit missionary who visited Lake Mainit in 

 1889, found its greatest depth to be 150 meters. The surrounding 

 country is mountainous. The outlet, Tubay River, reaches 

 Butuan Bay only after a long detour to the south. 



Lake Mainit has been considered as a crater lake by some 

 observers, and thermal springs occur around part of its peri- 

 meter, especially near the village of Mainit on its northern shore. 

 Smith states that possibly it is a caldera. However, limestone 

 is found on the eastern shore, a fact which would make it seem 

 improbable that the lake occupies a former crater. Maurice 

 Goodman crossed Lake Mainit during reconnaissance in Minda- 

 nao and it did not appear to him to be a crater lake, although 

 he thinks it probable that volcanic activity may be responsible 

 for its existence. 



I visited Lake Mainit in March, 1915. It is a beautiful body 

 of water surrounded by mountains, except on the northern side, 

 where there is a wide border of rich, low-lying, agricultural land. 

 The records of the Jesuit fathers show that the lake rose approx- 

 imately 4 meters in 1891 and flooded some of the villages on its 



" Op. cit., 353. 



