NORTHWESTERN PANGASINAN. 261 
The basal igneous.—Igneous rocks are found at the north- 
east corner of the area and extend in unbroken line, southward 
and westward, and continue throughout the whole length of the 
Zambales Range. The formation is exceedingly complex, and 
affords a choice field for petrographic study. The parent magma 
has in the process of cooling differentiated itself into types vary- 
ing in a Series extending through granite, syenite, diorite, gab- 
bro, and even to an ultra-basic, olivine rock. These have 
apparently cooled with varying rapidity and have given rise to 
finer-grained equivalents. As a much later phase of igneous 
activity, possibly wholly distinct, andesitic intrusion and ex- 
trusion took place. 
Granite.—Granite, which is rare in the Philippines, is found 
near Pao Bay, near Sual, and on the Balincaguin River, 5 kilo- 
meters south of Barlo. It does not appear to occur over a large 
area, and wherever found was extensively intruded by andesite 
dikes. Its light color stands out in marked contrast to the gen- 
erally black rocks of the region. 
A medium-grained holocrystalline specimen from Pao Bay 
was seen in thin section to consist of quartz and feldspars with 
small amounts of intersertal ferro-magnesian materials. The 
feldspars are occasionally twinned in Carlsbad manner, and gra- 
_ phic intergrowth of quartz and feldspar is common. Small 
grains of magnetite are present. 
A medium-grained specimen from Sual showed an inequigran- 
. ular consertal fabric and was seen in thin section to consist 
of quartz, orthoclase feldspar, and hornblende. Some plagio- 
clase and magnetite are present. 
A porphyritic phase of the granite is shown by the specimen 
from south of Barlo.. In thin section the rock has a seriate por- 
phyroid fabric. The orthoclase shows inclusions of small feld- 
spars and larger shreds of green hornblende. The groundmass 
consists of small prismoids of feldspar and irregular grains of 
quartz. 
Syenite.—Syenites are far more rare in the Philippines than 
granites, yet both rocks were found at Sual and south of Barlo. 
In the latter place the syenite appeared to occupy a position be- 
tween granite and diorite, and apparently indicates a mineral- 
ogical progression between the two types. 
A variety from south of Barlo showed a medium-grained 
granitic texture. The rock is very hard, dense, and dark. In 
thin section the fabric is inequigranular, consertal, and the rock 
consists of orthoclase and light green hornblende. Medium- 
sized magnetite grains are quite numerous. 
1133821——4 
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