RECONNAISSANCE OF SOUTHEASTERN LUZON. 459 



the head of Lagonoy Gulf, and on the shore between Daet and Bagacay 

 Points, form lowlands which have been aggraded. The Daet lowland 

 bears evidence of emergence, as has been noted by von Drasche, who 

 described the raised coral beaches along its coast. 



GEOLOGY. 

 SOUTHEA.STERX CORDILLERA. 



Geologic formation. — The portion of the northern division of the 

 Cordillera which includes the Labo and Colasi Mountains was mapped 

 by von Drasche as andesites and on the borders of the andesites he showed 

 two areas of andesite tuffs and two of breccias and pumice (Plate I). 

 Roth determined as andesites the rocks from this area collected by Jagor. 

 In the geologic map which accompanies the present report it has not been 

 possible to distinguish the varieties of andesites, nor to show the exten- 

 sion of the tuffs and breccias. The fragmental volcanics are found at 

 many places not seen by von Drasche, and are in such intimate relations 

 with the massive rocks that they can not be differentiated without detailed 

 field work.* Some basalts were encountered, but the andesites predo- 

 minate. 



Von Drasche noted that between Ragay and Lupi a gray, porous, 

 hornblende andesite overlies the Tertiarj' formations. To the west of 

 Mambulao, Tertiary sedimentaries are present over a considerable area, 

 the limits of which were not fully determined. There are intrusions of 

 andesites in these beds and they have been much disturbed from the 

 horizontal position in which they were deposited. Some float coal has 

 been found on the Dumuguan Eiver near Nalasvetan and this is evidence 

 that the Tertiary beds are represented at the headwaters of the stream. 

 Similarly, there is some coal to the east of Quilbay and Talcauayan near 

 the head of Ragay Gulf and with it there are Tertiary sedimentaries. The 

 cordilllera between Ragay Gulf and Sogod Bay is bordered by Tertiary 

 formations, which have been folded and faulted. The facts above noted 

 Justify the conclusion that a part of the volcanics and eruptives which 

 form the cordillera are younger than the Tertiary of this region. The 

 rocks near Paracale and Mambulao Mali be considered in discussing this 

 mining district. 



In the central division of the cordillera, Mount Isarog, which stands 

 alone at the northern end, and the Pocdol Mountains, which form the 

 southern part, contain principally andesites with which some basaltic rocks 

 are associated. Isarog was mapped by von Drasche as andesite and it was 

 so considened by Roth. The rocks of the Pocdol Mountains were not 



' The petrographic determinations of the collection of igneous rocks made 

 during this reconnaissance were undertaken by Warren D. Smith, chief of the 

 division of mines, Bureau of Science. 



