68 ADAMS. 



hill of it near the naval station which is quarried for use as crushed 

 stone. It is found as bowlders in many streams and it undoubtedly 

 constitutes a large part of the cordillera in the region of the Pinatubo 

 group of mountains. It is possible to identify Von Drasche's "trachytes" 

 by means of the distribution and habit of this rock. Usually it has a 

 coarse porphyritic texture, contains conspicuous glassy feldspars, and 

 is very friable. 



The diabase gabbro rocks mentioned by Von Drasche are represented 

 in the collection at hand. Some gabbros, peridotites pyroxenites and 

 serpentines were found near Subig in the Cinco Picos Mountains. 



Basaltic rocks were found to the west of Floridablanca at the foot of 

 the cordillera, in the vicinity of Subig, and in Mariveles Mountain, but 

 they are not conspicuous. 



Hochstetter, in his map of the volcanoes of Luzon, indicates Corregidor 

 Island, Mount Mariveles, Mount Batilao or Natib and Mount Pico 

 de Loro as extinct volcanoes. As will be explained in this chapter, 

 Corregidor consists largely of marine conglomerates. Mount Mariveles 

 has somewhat the appearance of a volcanic cone and the form of its 

 summit suggests a crater with the northern part of its rim broken down. 

 The quarry at Sisiman on the coast at the south base of the mountain 

 shows columnar structure, and the hill in which the quarry is located 

 may be a small volcanic neck or stock. There are no solfataras in the 

 western cordillera and volcanic activity has long since ceased. ' The 

 younger igneous rocks are eruptives and at certain centers, as for example 

 Mount Mariveles and Mount Pinatubo there probably at one time were 

 volcanoes which gave origin to the tuffs found on the flanks of the range, 

 but it certainly is not correct to class these eruptive centers as extinct 

 volcanoes along with those which are found in the southeastern and 

 southwestern volcanic regions of Luzon. 



Limestones. — Both cites Callery as reporting the occurrence at a dis- 

 tance of 4 leagues west of Sual, of a belt' of coarse limestone and travertine 

 having a width of 2 leagues, resting horizontally and containing decapod 

 crustaceans. This locality which is near the northern termination of 

 the western cordillera and on its eastern base not far from the Gulf of 

 Lingayen. is too distant from the area discussed in this report to warrant 

 examination at this time. It is the only occurrence of a limestone 

 formation which is at all definitely reported from this cordillera. The 

 fact of its being horizontal suggests that it is probably younger than the 

 cordillera and, without wishing to prejudice future observers, it is sug- 

 gested that it may be the equivalent of the tufaceous foraminiferal marls 

 described by Von Drasche as occurring near Santa Cruz on the west side 

 of the same mountains. In passing it may be well to note that Von 

 Drasche says that besides the marls he found no sedimentary formations, 

 but the cura of Porac told him that limestones were found in the cor- 



