THE GEOLOGY OF LUZON, PI. 51 
1. Very little exploration has been carried on in the dissected 
areas of northern Luzon, where we would expect to find the older 
formations. 
2. The Philippine Islands are situated at the outer edge of the 
Continental shelf, where the sediments are all recent and the older 
rocks would naturally be very deeply buried. 
3. Erosion has not as yet progressed very far, owing to the com- 
paratively short period that the archipelago has been above the sea. 
Below are given two sections across Luzon at different latitudes 
(Fig. 5. Infanta to Tanay [Ickis], and Fig. 6. North Central 
Luzon [Eveland]). 
INFANTA 
LACUNA 
DE BAY re Basalt 
PACIFIC 
QCEAN 
Sra level 
cava 
Fic. 5.—Section from Laguna de Bay to the Pacific. (After Ickis.) 
Cordi/lers Central 
Mencayen 47: 2° eae 
ay eu ~ 
ra’ 
Pr 
Yah Paietears 
t t 
Shales and Limestone 
Sandsiones 
Conglomerate 
(Agro Beds») 
Fic. 6.—Section across North Central Luzon. (Eveland.) 
THE IGNEOUS COMPLEX 
By the igneous complex, we mean all those igneous rocks 
overlaid by the tertiary sediments, some of these are diorites, some 
andesite and diorite intrusions and others are granites. They are 
naturally encountered over larger areas in northern Luzon, where 
erosion has been at work longer and more vigorously. ‘The central 
Cordillera then is the principal habitat, if we may use the term 
in this connection, of this class of rocks. Farther south, particu- 
larly in the vicinity of Manila, these rocks are deeply buried and 
only appear in isolated localities as in Ambos Camarines, the 
Loboo Mountains of Batangas, etc. 
Diorite, quartz diorites, metadiorites, granites, gabbros are all 
found in Luzon. Diorite is the commonest deep-seated rock. 
