﻿PETROGRAPHY OF SOME ROCKS FROM BENGUET 

 PROVINCE, LUZON, P. I. 1 



By Warren D. Smith. 

 (From the Division of Mines, Bureau of Science.) 



CONTENTS. 



Introduction. 

 Benguet hocks. 



Diorite. 



Quartz diorite. 



Dacite. 



Andesite. 



Andesite tuff. 



Andesite porphyry. 



Graywacke. 



Foraminiferal limestone. 



Illustrations. 



introduction. 



Mr. Eveland in his paper. "Notes on tlie Geology of the Baguio 

 Mineral District" 2 has described the field relations of the rocks, the 

 more detailed petrography of which I have taken for the subject of this 

 paper. 



In the following pages I propose to give a description of each rock, 

 which I wish could have been much more minute and exhaustive but 

 time did not permit of more extensive work. I have included diagrams 

 and photomicrographs and in addition have added some tables, using 

 the quantitative classification. 3 Many of our Philippine rocks are clas- 

 sified with difficulty according to this system, owing to their greatly 

 decomposed and altered condition, and it is only applicable to com- 

 paratively fresh rocks, which we rarely obtain except in mines and road 

 cuttings, and of these unfortunately we as yet have few. 



1 Supplementary to the paper by A. J. Eveland on the "Geology and Geography 

 of the Baguio Mineral District." This Journal, Sec. "A," Gen. Sci. (1907), 4, 207. 



- Eveland, A. J. : Notes on the Geography and Geology of the Baguio Mineral 

 District. This Journal, Sec. "A," Gen. Sei. (1007), 4, 207. 



3 Quantitative Classification of Igneous Rocks; Chicago (1903). 



235 



