﻿BENGUET PETROGRAPHY. 249 



variation in the size of the grains, but this has no special significance, save the 

 fact that the material was derived close at hand. 4 



Plate V, fig. 2, is a photomicrograph of a similar rock but not from this 

 precise spot. 



BENGUET NO. 108. — FORAMINIFERAL LIMESTONE. 



Macroscopic. — This is an aphanitic, pink-colored rock with conchoidal 

 to hackly fracture, it contains a few veinlets filled with rusty calcite. 

 The rock on its weathered surface has a dirty, bluish-gray appearance. It 

 effervesces strongly with acids. 



Microscopic. — Under the microscope the rock is seen to consist chiefly 

 of large and small grains of calcite with almost every conceivable shape, 

 stained copiously with iron oxide, which of course gives it its red color. 

 The rock also contains the remains of the two well known Miocene fossils, 

 Operculina complanata Bast, and Lithothamnium ramossissimum Kuess. 



Plate V, fig. 1, is a photomicrograph of this rock. 



Remarks. — I have found these same forms in limestones from Cebu Island, 

 Polillo Island, Lepanto Province, Luzon, and other localities. 



LIMESTONE FROM THE BENGUET ROAD. 



Macroscopic. — In the hand specimen this rock is quite black, in por- 

 tions very fine-grained, in others crystalline; it is occasionally streaked 

 with minute calcite veins. It is very fossiliferous, but as the rock is 

 very hard it is difficult to remove the fossils, which are for the most part 

 large bivalves. 



Microscopic. — The dark color is due to an excessive amount of iron 

 oxide in the matrix. Large amounts of calcite in more or less rounded 

 grains are to be seen in the slide, these practically make up the entire 

 rock. Fragments of foraminifera are quite abundant, but, owing to 

 their state of preservation we can make little more than a guess as to 

 their identity. Some of these very much resemble sections of Operculina 

 and there is another section which suggests a nummulite as it possesses 

 "alar prolongations" between the successive whorls. 



Remarks. — This limestone in its lithology, fossils, and position is quite different 

 from the upper limestone on the Baguio Ridge. It would seem very probably to 

 be Eocene. 



BENGUET NO. 124. — FELDSPAR PORPHYRY. 



Macroscopic. — A hypocrystalline, fine-grained, bluish-gray rock which 

 has xenomorphic shape and hypautomorphic arrangement of its crystals. 

 The rock is rather prominently speckled with small amphiboles or pyro- 

 xenes, difficult to separate in a megascopic examination. 



Microscopic. — Another badly decomposed rock, consisting of pheno- 

 crysts of saussuritized plagioclase in a groundmass of small, lath-shaped 

 feldspars, for the greater part plagioclases, and quite fresh magnetite 



4 Wavy extinction is to be seen in some of the quartz and feldspars. This 

 means strain due to pressure. Also there is evidence of secondary enlargements 

 of some of the minerals, another sign of metamorphic action. 



