THE MALAYAN ARCHIPELAGO. 113 



From the inner group of the arcliipelago, that is to say, 

 Borneo, Celebes, and Gilolo, radial ridges of cordilleras and 

 chains of volcanoes converge, like the frame of a fan, towards 

 the Philippines, which therefore, present a variety of orographic 

 features. Geologically they have been reconnoitered by v. Dra- 

 sche,'^^ and some others, while Prof. Suess has ably sketched 

 the geology of the whole Philippines from his wide knowledge 

 of the literature of these obscure Spanish islands. From a study 

 of them we learn that they have parallel ridges separated by 

 tectonic valleys, one of which extends from the Bay of Butuan 

 to that of Davao in Mindanao, while another goes from the Bay 

 of Lingayen to Manila, disconnecting the main chain of Luzon 

 from the westerly Zambales. 



The Sierra de Zambales is a meridional ridge, made up of 

 an old stock of gabbro, serpentine, and diabase-like rock, besides a 

 red, hard siliceous slate ( ? Radiolarian chert), and at some place 

 a limestone of unknown age. On the east side of the sierra, 

 the whole seems to be overlaid by an enormous thickness of 

 trachytic tuffite, from which the feldspar sands are derived. The 

 laiter cover the flat and form the ground of Pampanga, north 

 of Manila. Along the west coast near Masingloc, a thinly bedded 

 marly tuffite makes its appearance, and attains a considerable 

 thickness. This was made the subject of study by Karrer, which 

 resulted in the recognition of many species of Foraminifers, 

 identical with those of Kar Nikobar, usually referred to the 

 earlier Miocene."^ The volcanic, southern Zambales trends a 

 little to the south-east, but its main ridge runs close by the 



71) ' Fragmente zu einer Geologie der Insel Luzon ', 1878, Wien. 



72) E. V. Dräsche, ' Fragmente.' etc. 



