20, 3 Schenck: Physiography and Geology of Samar 247 
After leaving the boat and taking the trail once more, the 
course lay over limestone, but farther on shattered shale was 
again encountered, which, with clay, seems to be the principal 
geologic feature between Loquilocan and Bagakay, although a 
bowlder of an igneous rock was picked up in a stream between 
these two places, about 2 kilometers west of Bagakay. This 
proved to be a compact, fine-grained, dark gray rock, weathering 
to brown. Microscopically, it is a seriate porphyritic rock, 
tinged green by chlorite and composed chiefly of partially decom- 
posed plagioclase feldspar, which occurs as lath-shaped simple 
and compound forms, and larger subhedral crystals, some of 
which exhibit wavy extinction. Olivine, augite, and chlorite 
are present. Although the hand specimen resembles andesite 
closely and the thin section shows some internal andesitic charac- 
teristics, this rock, because of its composition, is probably an 
olivine-basalt.?. This may be the rock described by Roth as an 
augite-andesite or dolerite. 
After leaving a settlement. of two houses, east of Bagakay, the 
party observed in the bed of a creek a formation that is unmis- 
takably igneous. It is a reddish rock composed of minute ferro- 
magnesian crystals in a dense, vitreous groundmass, with many 
vugs filled with secondary material. It probably is an amygda- 
loidal basalt. 
The rocks that were most puzzling in the field were specimens 
from the Wright-Taft trail, 5 to 6 kilometers east of Bagakay 
and less than half a kilometer from the basalt just described. 
Weathered specimens of this formation resemble sandstone, ar- 
kose, graywacke, or tuff, according to the mood of the observer 
at the time! At one place (station 30 H. G. S.), there is a 
definite outcrop which strikes north 45° west and dips 30° north- 
east. Megascopically, it is a medium-grained, blue-gray rock, 
and weathers to deep brown. It effervesces but slightly and is 
characterized by small, white feldspar and quartz crystals in 
a blue groundmass or matrix. Microscopically, it exhibits rather 
definite flow structure. It is composed of angular and subangular 
to rounded crystals, all well fractured and embedded in an 
apparently fine-textured matrix. Plagioclase feldspar predomi- 
nates. On some of these crystals it is of interest to note inter- 
secting brushes like an interference figure, showing that the 
minerals of this rock have undergone strain. It is possible that 
"Cf. British Petrographic Nomenclature, Mining Mag. 24 (1921) 278-281. 
184895 ——2 
