GEOLOGIC RECONNAISSANCE OF SOUTHWESTERN LUZON. 61 



from the main cordillera. The highest mountain in this group has an 

 elevation of 1,110 meters. 



From a geological standpoint the Pico de Loro Mountains, highest 

 elevation 678 meters, situated south of the entrance to Manila Bay, 

 belong to the western cordillera. Corregidor and Caballo Islands, 

 together with some small islands and rocks, constitute the evidence of 

 a submerged connection. The silhouette of Corregidor Island, which 

 is just visible, and the mountains which lie to the north and south on 

 the mainland as seen from a distance of about 50 kilometers across 

 Manila Bay, are familiar to all who have admired the charm of the 

 sunset view from Manila. 



Central plain. — This region is low lying and but little diversified. 

 Mount Arayat, just north of the area here discussed, rises as a solitary 

 peak to a height of 1,040 meters. On clear days it can be seen from 

 Manila. It is situated about equidistant from the western and eastern 

 cordilleras. 



The portion of the central plain included in the geologic map is for 

 the greater part occupied by a network of river mouths and esteros. 

 These channels constitute the delta of the Pampanga Biver which has 

 its headwaters in the northeastern part of the plains region. The 

 Pasig and Orani Bivers of this drainage system are navigable for boats 

 of shallow draught which ascend to Guagua and beyond that point to 

 Arayat. Near the bay the numerous islands of the delta are covered 

 with mangroves and the low nipa palm. 



The area of water-laid tuff lying to the east of the alluvial portion of 

 the central plain is appropriately included in the central valley region, 

 although it is related to the southwestern volcanic region. This country, 

 which is a little higher than the alluvial plain, is but slightly diversified 

 excepting near the stream valleys which cross it. It rises gradually to 

 the eastward, where it is limited by the foothills of the eastern cordillera. 



Eastern cordillera. — In so far as known the mountain structure of 

 this area is with the trend of the cordillera. It is not now possible to 

 divide it into minor ranges, and the drainage which is as yet imperfectly 

 mapped, does. not suggest any important longitudinal valleys. Seen in 

 a broad way it presents two physiographic provinces which for con- 

 venience may be designated as the northern and southern, the division 

 occurring opposite the eastern lobe of Bay Lake. 



The northern division of the cordillera contains a number of con- 

 spicuous mountains and subordinate ridges which show alignments 

 suggesting ranges. The higher mountains are probably in most cases 

 composed of eruptive rocks. The region is not well explored, but within 

 the area of the geologic map accompanying this report there are indicated 

 Mount Driod, elevation 1,185 meters; Mount Angilo, elevation 1,307 

 meters; Mount Batay, elevation 1,408 meters; Mount Banay, elevation 

 1,345 meters, and Mount Kanumay, elevation 1,049 meters. 



