GEOLOGY OF THE PHILIPPINE ISLANDS. 31 



• i 



laon, the two volcanoes of Negros. The positions of the volcanoes of Mindanao 

 relative to the two main fissures are not clear, but it is probable that the line 

 of volcanoes extending in northern Celebes through the Sanguir Islands and 

 Sarangani to Mount Apo, and perhaps crossing Mindanao to Camiguin de Mi- 

 samis, are situated on a parallel outer fissure of this series. Another curve 

 parallel to this extends from the eastern side of the Gulf of Davao, through the 

 Surigao Peninsula, Leyte, and Masbate, and includes the extinct volcano of 

 Diuata in eastern Mindanao and extinct volcanoes in Leyte and Biliran. A 

 third outer line, parallel to the last two, is formed by Samar and the Camarines 

 peninsula of Luzon. Associated with this are the splendid group of volcanoes in 

 Sorsogon, Albay, and Camarines Provinces — Bulusan, Bacong, Mayon, Iriga, and 

 Isarog. 



A group of volcanoes is found south of Manila in Laguna and Batangas Prov- 

 inces; one of these, Taal, is still active. These do not seem to fit into either 

 of the two prevailing systems of the Visayan Islands and southern Luzon, and 

 require different schemes for classification. Perry 3 classifies the volcanoes of 

 Luzon into three northwesterly lines. The first includes the volcanic stock of 

 Mariveles and Taal Volcano; the second, Arayat and Banajao; and the third, the 

 Mayon group. Centeno * makes one system to include Arayat, Taal, central 

 Mindoro, Canlaon, and Malindang. Koto 5 omits Arayat and the Taal group from 

 his volcanic belt. Becker 6 seems to include the volcanoes of the Taal region with 

 the northwesterly series of fissures and makes no attempt to explain the position 

 of Arayat. There are no known volcanoes north of Arayat until the extreme 

 northwestern part of Luzon is reached. Northward from Kawa a volcanic chain 

 extends due north as far as the Bashi Channel, which separates the Batanes 

 Islands from Formosa. 



Three quite distinct types of volcanoes occur in the Archipelago. 



These are : First, the nearly perfect cone ; second, the worn-down stock, 



with no regular form; third, the collapsed cone. Mount Mayon is the 



type of the_ first group. This is a beautifully symmetrical cone 2,422 



meters in height, the curve of its slope coinciding, according to Becker, 7 



4 e — xie c —xic 

 with the hyperbolic sin curve — = „ > when c=8.6 mm. The 



C A 



last active eruption of this volcano occurred in 1900. It is an ash cone. 

 No lava flows are to be seen anywhere near its base, but recent climbers 

 have reported the presence of lava flows near the summit. 



Other volcanoes in this group are Mount Arayat and Bud Dajo, the 

 former in Luzon and the latter on the Island of Sulu. 



Mount Mariveles is the type of the second group, and by far the 

 greatest number of volcanoes in the Philippines conform to it. 



Taal is the type and the greatest example of the third group. 



3 Extrait des Annales de la Socifite d'emulation des Vosges (1860), 10, 3d 

 pt., 35. 



4 Mem. geol.-min. de las Islas Filipinas, Madrid, Tello (1876), 8. 



*Journ. Coll. Sci. (1899), 11, pt. 2, 112. 



"Loc. cit. 546. 



T A Feature of Mayon Volcano. Proc. Wash. Acad. Sci. (1905), 7, 277-282. 



