THE GEOLOGY OF LUZON, P.I. 53 
Iddings, Oebbeke, and the writer have described specimens of 
these rocks from various parts of the Islands, but Iddings is the 
only one who has attempted anything like a systematic study of 
them, with a view of drawing conclusions concerning petro- 
graphic provinces, correlation, etc. He found that pyroxene 
andesites with hypersthene and augite both present predominate, 
next hornblende-pyroxene andesites, and third, hornblende andes- 
ites without pyroxenes, and last, a few with biotite in addition 
to the minerals already named. 
There is a complete gradation from the andesites to the basalts. 
Some of the latter are extremely rich in olivine. 
Dacites have been found in a few localities, Corregidor Island 
at the entrance to Manila Bay being the type locality. 
The greatest distribution of agglomerates and tuffs is to be found 
in the region of Laguna de Bay and over a large part of Batangas 
Province (Fig. 7). The agglomerates are especially well shown in 
a deep and very picturesque gorge at Pagsanjan, Laguna, and from 
there all the way to Mount Banajao, one finds nothing but volcanic 
agglomerate with patches of tuff here and there. This tuff and 
agglomerate have been more particularly discussed by Adams in 
the article already referred to. 
THE METAMORPHIC ROCKS 
Metamorphic rocks have been found in Ilocos Norte, in Ambos 
Camarines and in Benguet, probably in many other parts they 
will be found when more exploration has been carried on. 
In Ilocos Norte, we have actinolite and mica schists, bordering 
a granulite dike, in Benguet marble, due to diorite intrusion, in 
Ambos Camarines gneissic granite and schistose diorite. 
The rocks of the volcanic mountains are by far the most widely 
distributed! of all the rocks in Southern Luzon, and possibly in the 
Island as a whole. The country surrounding Manila and south- 
western Luzon is the principal home of these rocks. The chief 
centers are Arayat, Taal and Banahao, Mariveles, and the south- 
western volcanic cluster. The principal rocks are andesites with 
later flows of basalt. 
t For general distribution of the major formations the reader is referred to the map 
in Regionale Geologie (Steinmann in Bonn), VI, pt. 5, by Warren D, Smith. 
