﻿222 EVELAND. 



Archipelago which were known at the time his paper was written, and 

 while he points out that there may he a more or less close connection 

 between the Philippine group and Borneo on lithologic grounds, he 

 admits that there is ho inconsistency in Abella's view 2 that the dioritic 

 rocks represent the oldest of the Philippine series, if those schists of 

 similar composition arc included under the head of "dioritic rocks." It 

 is a pleasure to record in the results of work even so little detailed as 

 that given in the present paper, data which coincide with the deductions 

 of Mr. Becker, who had only vicarious observations of varying reliability 

 to serve as criteria and also with the observations of Abella, who, 

 although limited in his scope of work, has proved, for the most part, 

 to be the most trustworthy of the Avorkers in this field. 



BASAL MASS. 



There seems then to be good ground for believing that the diorite 

 I have observed in the Baguio district represents the starting point of 

 our Philippine geology, at least for northern Luzon. I have described 

 it in a former paper, 3 discussing its appearance in Lepanto; it occurs 

 over a large area of the present Benguet field; various observers have 

 noted it over a sufficiently large portion of Luzon; and Abella in 

 particular has verified his field notes with the microscope in order to 

 justify the above hypothesis. 



In the Baguio district the exposures of the basal diorite, as would 

 naturally be supposed, are generally most prominent at the lower eleva- 

 tions, although on the Avestern border of the area, the most prominent 

 exposure is the highest point in the district, namely the crest of Mount 

 Santo Tomas. Here the rock is light green in color, finely grained, holo- 

 crystalline to the eye, hard and compact, with apparently little weather- 

 ing. Plagioclase and amphibole may be distinguished with a lens, 

 together with some chlorite and occasional quartz and magnetite crystals. 

 The valley of the Antamok Eiver shows the best exposures of this diorite 

 and it is here most typical of the large area. 



The rock megascopically is dark green, holocrystalline, massive; it is 

 very hard and apparently more resistant to erosion than any other rock 

 in the district. Only plagioclase, amphibole and a dark-green chloritic 

 mineral can be distingTUshed with the eye. Locally, over a small area, 

 the amphibole is developed to a greater extent. At one of the tunnels 

 of the Bua Mining Conqmny, the main cross-cut to the "main reef," 



" Abella: Apuntes fisicos y geologieos (1884), 30. 



3 Eveland: Preliminary Reconnaissance of the Mancayan-Suyoc Mineral Region. 

 Bull. Min. Bur., Manila (1905), 4. 



