118 B. KOTO : THE GEOLOGIC STRUCTURE OF 



that here occurs hornblende-andesite. The eastern sierra of 

 Mindanao lies in tlie direction of it. The ridge is composed of 

 an old slate, dioritic conglomerate (like the Agno bed), limestone, 

 and serpentine. Separated from the sierra by the Butuau-Davao 

 basin, there runs a western ridge, nearly parallel to the former. 

 It is a gold-[)r()ducing chain, being built up of quartzite and 

 clayslate. The eastern sierra ends with Cape S. Augustin, 

 opposite to Gilolo, and the western mountain terminates in Cape 

 Tinaca, })ointing southwards to Miuahassa in North Borneo. 



It now remains for me to consider the volcanic chains. 

 As 1 have already said, the Molucca chain, starting from Ma- 

 kian, goes through Ternate and the north of Gilolo, then through 

 Tulur or Talaut, and Namusa, and finally reaches the solfataric 

 volcano, Apo, in Mindanao, passing by the way a volcano 

 near Cape 8. Augustin. The Sangir chain, on the other hand, 

 comes from the north arm of Borneo and passes through Ruang, 

 Siao, Sangir, Butulan (Sarangani), and the volcano Sanguil near 

 Cape Tinaca, and finally unites with the Molucca system at Apo, 

 9,000 ft. high, the loftiest cone of the Philippines. The united 

 chain reaches the volcano of Caminguin in Butuan Bay, an 

 island formed in 1871, accompanied by a great eruption. It further 

 touches the trachytic island of Biliran, lying to the north of 

 Leyte, and then continues to the Albay chain of Camarines, 

 already referred to. The crater of Cagua, near Cape Eugano in 

 North Luzon, may be looked upon as its prolongation and the 

 same chain goes through the Babuyans, Batans, and the Bashi 

 Islands. It leaves then the Philippines, and enters the island of 

 Kôtô-sho (Botel- tobago) of the new Japanese domain. The island 

 of Claro of the Babuyan group is said to be a lofty active 

 volcano, which serves the purpose of gigantic natural light-house. 



