THE PHILIPPINES. 245 



ridge is also broken by numerous openings, tbe broadest and deepest of wbicli 

 lies off the coast of Mindanao. As shown by the submarine explorations of the 

 Challenger , the two basins enclosed between the Philippines and Borneo resemble 

 the Mediterranean in the temperature of their lower depths. The cold waters of 

 the oceanic depths are unable to penetrate across the intervening isthmuses into 

 these inland seas, where the thermometer nowhere records less than 50^ F. 



These three lines of partly emerged, partly submarine, ridges, stretching from 

 Indonesia towards the Philippines, continue their main axis in the interior of this 

 archipelago, and constitute a great part of its relief. Mindanao, least known of 

 the whole group, although one of the most remarkable for its volcanic phenomena, 

 is formed, at least in the west and centre, by the prolongation of the two eastern 

 ridges, indicated seaward by the Sulu and Sanguir Archipelagoes. The Sulu axis, 

 whose normal direction is south-west and north-east, comprises all the western 

 peninsula of Mindanao, while the Sanguir axis, running south and north, strikes 

 the southern point of the same region at the Saragani volcano. Beyond this 

 point it first continues its northerly trend and then gradually sweeps round to the 

 west. East of this mountain range another parallel chain occupies all the eastern 

 section of Mindanao bordering on the Pacific Ocean. 



A broad survey of the whole orographic system shows in the same way that, 

 from the southern point of Mindanao to the northern extremity of Luzon, the relief 

 of all the islands is disposed in a line with or parallel to the southern isthmuses. 

 Thus the coast range of the east side of Mindanao is continued north-west in a 

 graceful curve through the islands of Leyte, Masbate, Ticao, and Burias ; in the 

 east is developed a parallel curve formed by the island of Samar, the Camarines 

 peninsula in Luzon, and the Isla del Polillo. On the other hand the islands of 

 Bohol, Cebu, Negros, and Panay are disposed in a line with or parallel to the 

 Sulu Archipelago, while Mindoro and the main section of Luzon form the north- 

 eastern extension of Paragua and Borneo. In many places volcanic or other 

 masses mark the points of intersection, and it is noteworthy that in Luzon, most 

 rugged of the Philippines, all the Cordilleras converge like the ribs of a dome in 

 the culminating crest of Caraballo. North of the Philippines the mountain ranges, 

 interrupted by broad straits, are continued through Formosa and the Liu-Kieu 

 group towards Japan. 



The whole surface of the Philippines is essentially mountainous, the only plains 

 that occur being the alluvial districts at the river mouths, and the spaces left at the 

 intersection of the ranges. Most of the surface appears to be formed of old rocks, 

 especially schists, and, in the north of Luzon, granites. Extensive coal-fields are 

 found in the central islands, especially Cebu and Negros, and in many places these 

 carboniferous beds seem to have been buried under more recent lavas. Later 

 limestones have also been developed by the coral-builders round all the seaboard, 

 and there is clear evidence that along extensive stretches of the coastline these 

 formations have been upheaved to a considerable height above sea-level. They 

 form at some points broad horizontal tables round the headlands, and here are 

 found shells and other marine remains belonging to the same species still living in 



