THE MALAYAN AECHIPELAGO. 115 



rbyolite, and hornblende-andesite,* whose derivatives — tuffite and 

 marl, and the contemporaneous deposit of coral limestone cover 

 the greater part of the area. As the submersion still con- 

 tinued, coral reefs and the breccia of coral limestone were formed, 

 being associated with the detritus of young volcanic rocks. The 

 corals which afford the substratum of the reef are Gcdaxœa, 

 Favia, Mœandrina, Porites and fAsfneopora, wliich scarcely differ 

 from the living ones, and have even left behind an atoll at La 

 Trinidad at an elevation of 4,000 feet. Volcanoes seem not quite 

 at rest, for Monte Sto. Tomas, 3,120 Spanish feet high, was said 

 to have made an eruption or explosion in 1G35 or 1641. 



The inland chain of the west coast, the Cordillera del Norte, 

 seems mainly to l)e made up of tuffite and coral reefs, with the 

 extinct volcano of Monte Date in Lepanto ; its southern pro- 

 longation, the Cordillera Central is of hornblende-andesite. 



This main western chain meets at the gabbro massive of 

 Caraballo Sur with the Sierra Madrés, which runs up the un- 

 explored east coast of North Luzon. 



It is a great pity that our knowledge of the geology of 

 North Luzon is so meagre and defective, that we can draw no 

 inference from it about the geology of Taiwan. 



From the Caraballo Sur massive wliich serves for the water- 

 shed of all the great rivers of Luzon, the axial mountain ridg(> 



* Oebbecke has made a. microscopic analysis of rocks collected by Semper, and he 

 mentiones the occurrence of hornblende-andesite of a pnmiceous stnu-ture in the military 

 districts of Lepanto and Bentok in Northern Luzon, and on tlie vnlcanoes of Iriga, Bulusan, 

 Labo, Isarog in Camarines, and in the island of Leyte. All the rest of the volcanic 

 districts are mainly made up of the oli vine-bearing augite-andesite of a hyaline type. 

 Feldspar-basalt comes from Mindanao besides andésites. Neues Jahrb. f. Mineralogie, etc. 

 Beilage-Band I, S. 452 et seq. 



