vm, a, 4 Saderra Maso and Smith: Seismic Disturbances 211 



(c) Small and large intrusions of diorite, granite, and basalt 

 are innumerable throughout the Islands. In the Central Cordi-. 

 Hera of Luzon the intrusions seem to be generally diorite. They 

 cut both the Tertiary sediments and the overlying extrusives. 

 In the Province of Ambos Camarines in southeastern Luzon 

 granitic intrusions cutting the diorite and possibly the sediments 

 can be seen. In the Sulu Archipelago we have found a number 

 of small basaltic intrusions cutting some of the recent sediments. 

 Owing to the absence of an accurate base map of the Philippine 

 Islands and the fact that our work has been largely of a recon- 

 naissance nature, these intrusions have not been mapped in 

 detail or with sufficient accuracy for us to state whether or not 

 they follow any general system of jointing or earth lineaments. 



(d) Flanking all the Cordilleras on both slopes there is a 

 greater or less development of sandstones, shales, and limestones 

 which have been bowed upward in the general Miocene uplift 

 referred to above, with some minor crumpling at various points. 

 The folding in the northern part of Luzon has apparently been 

 a gradual and gentle uplift of the strata. In Tayabas Peninsula 

 the flexures are sharper. In the Zamboanga Peninsula the 

 strata have been so intensely compressed that schists are the 

 result. These schists have been considered by some to be older 

 than the Tertiary, but there seems to be no good reason for not 

 referring them, in part at least, to the Tertiary. The central 

 portion of Mindanao consists of gently folded sediments. The 

 major axis of folding in the Philippines is in general north and 

 south ; along the outside arc of the Islands, northwest and south- 

 east ; on the inside, northeast and southwest ; but in central Min- 

 danao in the Cotabato Valley the axis of folding is more nearly 

 east and west. 



(e) Metamorphic rocks occur more or less pronounced in 

 various parts of the Islands. In the Province of Ilocos Norte 

 there is a considerable development of schist, and in Ambos 

 Camarines there is schist and gneiss along the border of the 

 granite intrusion referred to above. Schists have been found at 

 one locality in the Central Cordillera of Cebu ; at various points 

 in Palawan; on the Zamboanga Peninsula alluded to above; in 

 the Province of Bukidnon, Mindanao; on the Surigao Peninsula 

 and just east of the Gulf of Davao; at one point on the Tayabas 

 Peninsula; and on the Caramoan Peninsula, southeastern Luzon. 

 These schists appear to be for the most part metamorphosed 

 sediments. 



