220 The Philippine Journal of Science 191s 



development of raised beaches and raised coral reefs along this coast, 

 making it plain that elevation has taken place along this line in recent 

 times. Whether this elevation has been accompanied by differential move- 

 ment, we are unable to say. 



There are no evidences of recent volcanic activity in any part of the 

 region, but granites, schists, and some very old andesite are present. 



Line B — B connects epicenters of northern and southern Luzon, cuts 

 through Dalupiri, the westernmost of the Babuyanes Islands, then very 

 closely follows the Central Cordillera southward through the Agno Valley, 

 thence to the eastward of the Zambales Range, and on through the Island 

 of Mindoro, where it cuts the latter west of the great volcanic stock of 

 which Mount Halcon is the principal peak. There is no information with 

 regard to the rocks on Dalupiri. However, the rocks of the Central 

 Cordillera in Luzon have a core of plutonic rock, chiefly diorite, flanked 

 by Tertiary sediments which have been arched upward, and in various 

 points along the crest of this arch extrusive rocks can be found in 

 abundance. No volcanic activity now manifests itself in that region, but 

 it is a region of hot and of salt springs. It is a line along which there 

 was considerable extrusion of igneous rocks in the past, but there is no 

 evidence of this now; therefore, seismic disturbances which take place along 

 this line at the present time are due to displacement along a line of weak- 

 ness rather than to any volcanic activity. It is significant that all of these 

 -points where either past or present volcanic activity is manifested are 

 found to lie along more or less definite, and in many cases, straight lines. 



Line C — C is the next prominent line which runs at right angles to 

 the B line, and lies either on, or very close to, 4 epicenters. At the upper 

 end of the central plain of Luzon the mountains rise rather abruptly, 

 and present a front which has a general east and west direction. It is 

 possible that this line represents a fault line where the central plain 

 represents the downthrow side. That area has not been studied in detail, 

 but it appears as if there is a definite break along that line. In a more 

 arid region one would expect to find definite escarpments facing southward, 

 but in a region of high rainfall like the Philippine Islands these escarpments 

 naturally would very soon be obliterated so that their existence can only 

 be inferred. 23 



D — D is a very prominent line which runs along the Archipelago close 

 to the 122d meridian. It connects the epicenters of the Batanes Islands, 

 Cagayan Valley, Casiguran Bay, east of southern Luzon and Mindoro, 

 and west of Mindanao. The northernmost part of the line, outside of 

 Luzon follows very closely the Batanes and Babuyanes volcanic chain, 

 studied by Ferguson" and represented by the cones Yami, Mabudis, Inem, 

 Iraya, Balintang Rocks, Babuyan Claro, Camiguin, and Didicas. Within 

 Luzon it passes not far west of Caua Volcano, southward along the 

 structural Cagayan Valley, following the trend of the Eastern Cordillera 

 until this turns toward the southwest, or rather when it seems to be 

 interrupted by the gap forming Casiguran and Baler Bays. From the 

 latter bay it follows the eastern coast of Luzon and passes to the Mindoro 

 Sea through the volcanic region of Tayabas Province. Farther on toward 

 the south it passes fairly close to Tablas Island which is oriented in this 



"Herrmann, Raf., This Journal, Sec. A (1911), 6, 331. 

 a Manuscript report. 



