210 The Philippine Journal of Science 1913 



naturally not very widely distributed on the surface and usually 

 are found only in the canons of the central ranges. They are 

 particularly abundant in northern Luzon, throughout the Central 

 Cordillera ; in Palawan Island ; the Western Cordillera of Panay ; 

 the Central Cordillera of Cebu and Leyte; the Eastern Cor- 

 dillera of Mindanao; on Masbate Island; in fact, wherever the 

 streams have been able to cut through the overlying, more recent 

 formations. 



(&) In all parts of the Islands there is a large amount of 

 extrusive material which forms a mantle over the deeper lying 

 formations. Naturally these are found around the volcanic 

 areas, and these extrusives are very pronounced in the Zambales 

 Range of southwestern Luzon and in various parts of the Cen- 

 tral Cordillera lying above the old igneous and the Tertiary 

 sediments. In the Central Cordillera of Luzon there exist great 

 patches of andesite, marking probably early Tertiary volcanoes. 

 In the Zambales Mountains there is a development of andesite, 

 marking probably a still later period of volcanic activity. On 

 Mount Arayat, which rises isolated out of the central plain of 

 Luzon, basalt occurs, and around Taal Volcano and on the Bi- 

 nangonan Peninsula there is a considerable amount of basalt. 

 Extrusives are particularly well developed in the southeastern 

 volcanic cluster of southeastern Luzon, comprising the well- 

 known peaks of Bulusan, Mayon, Isarog, etc. They are found 

 overlying much of Masbate, particularly in the central portion; 

 also in western Panay, a portion of Cebu, most of northern 

 Negros, central Leyte, and notably in Mindanao, there being a 

 broad belt of extrusives running north and south through the 

 Apo and Matutan Ranges. Also, there is a great patch of 

 basaltic material around Lake Lanao and a great volcanic mass, 

 of which Mount Malindang is the center. There is also great 

 development of these extrusives covering almost the entire 

 Islands of Basilan and Jolo and the lesser islands of the Sulu 

 Archipelago. 



As yet, we know of extrusives in Palawan only in the northern 

 part. The principal mountainous mass of Mindoro, Mount 

 Halcon, is largely andesitic. 



There is one general conclusion which can be drawn from the 

 distribution of the extrusives in the Philippine Islands ; namely, 

 that the entire recent volcanic activity consists, as far as we 

 know, of basaltic materials, and the older stocks are without an 

 exception andesitic. 



