524 W. D. SMITH — GEOLOGIC INI^LUENCES IN THE PHILIPPINES 



extending north and south in the central portion, in which are Mount 

 Apo and Mount Matutum, the former, as stated, being the highest peak 

 in the Islands, 9,610 feet. A cluster of peaks is irregularly arranged 

 around Lake Lanao, and to the south of this lake there is the east-west 

 line of dormant craters of the Buldmi Eange. The Malindang stock in 

 northwestern Mindanao is nearly 6,000 feet in elevation, but has no great 

 width. It forms the backbone of the Zamboanga Peninsula. 



From geological evidence it seems very clear that there was a general 

 buckling throughout the archipelago. Where fissures opened along the 

 crest of the folds vast quantities of extrusives poured out, concealing the 

 underlying formations in many instances. Many of the islands, such as 

 Cebu, merely are the eroded crests of the anticlines which appear above 

 water with the straits between occupying synclines. The main crustal 

 shortening took place in an east and west line, but cross-folding in the 

 opposite direction also occurred. 



It will be noted on the relief map, plate 34, that while the general 

 trend of the mountain ranges is north and south, there is a bifurcation in 

 the island of Masbate. From this point one set of lines extends, in the 

 eastern part of the archipelago, in a northwest-southeast direction, and, 

 in the portion toward Borneo, in the opposite direction. The two-pronged 

 configuration of the island of Masbate is one of the most significant things 

 about the whole subject. It is important to note also that at the intersec- 

 tion of these tectonic lines we have today the most productive quartz gold 

 camps in the Islands. 



As a rule, Philippine mountains are covered with dense vegetation, 

 either with forest or with the ubiquitous cogon (Talahib) grass. But in 

 some places, particularly well exemplified in the Zambales Mountains of 

 western Luzon, there are forests near the foot of the ranges, and then, at 

 from 3,000 to 5,000 feet elevation, the slopes are absolutely bare and 

 rocky in many instances. Above this point, however, the well defined 

 "mossy forest^' covers the slopes to the summits. 



While most of the mountains either are worn down volcanic stocks or 

 more or less undissected cones, yet there are a few examples of the faulted 

 and tilted block type. The latter are exemplified by those to the west of 

 the railroad near Bamban, on the Manila and Dagupan Railroad in Lu- 

 zon, and those on the eastern flank of the Cordillera Central of Panay. 

 We shall consider later on how the mountain ranges have controlled the 

 distribution and development of the various groups of peoples in the 

 archipelago. 



Mountain passes of the archipelago are : 



a. O'Donnel-Iba Pass, in the Zambales, western. Luzon. 



