﻿228 EVELAND. 



Many outcrops of andesitic rocks are exposed on the Baguio-Kias 

 Ridge, all more or less closely related in that they evidently represent 

 one period of volcanic activity. These rocks vary from typical augite- 

 andesites and andcsite-porphyries to hornblende-porphyry, and certain 

 other exposures can only strictly be classified as dacites. The rocks are 

 so closely related that they are mapped as "andesitic rocks" to show their 

 occurrence as subsequent and younger formations. 



The rock in general is porphyritic in structure, the light-colored 

 feldspar-phenocrysts showing prominently against the darker ground- 

 mass. Occasional exposures were seen which show a more granitic 

 texture, but these are comparatively rare. Sections from one of the 

 typical exposures on the Copper King Creek at the mill of the mine of 

 the same name, show a rather abnormal cryptocrystalline groundmass 

 with abundant phenocrysts of zonally constructed plagioclase, of horn- 

 blende and of magnetite. Investigation of extinction angles of the 

 feldspar shows it to be labradorite, with occasional twinning according 

 to the pericline law. Actinolite is the representative of the amphiboles, 

 it rarely is unaltered, and then it shows pleoehroism. 



Saussuritization has taken place to a considerable extent and in many 

 instances only outlines of the original feldspar are left. Magnetite is 

 abundant in minute grains and is closeby associated with the actinolite. 



Specimens showing a pronounced porphyritic structure were collected 

 from a dike in the Bued River a half mile above Kias, the plagioclase 

 phenocrysts measuring as much as 0.5 inch in length, set in a dark 

 groundmass. Under the microscope the feldspars show the characteristic 

 alteration of the albite twins, and much caleite and epidote is seen. Oli- 

 goclase and andesine are identified in the fresher crystals. There is 

 a second series of phenocrysts of a smaller size developed in the ground- 

 mass, and these, although badly corroded, are undoubtedly remnants of 

 museovite. Magnetite is present to a considerable extent, and both 

 hematite and limonite scattered through the groundmass and the mus- 

 eovite phenocrysts are in almost all sections. 



A large exposure of a fine-grained andesite which is apparently a 

 transitional rock, is found at a greater distance up the Bued River from 

 this dyke variety of the andesitic eruptives. Its groundmass is light in 

 color and the amphiboles make up the majority of the phenocrysts which 

 are visible to the eye. This variety represents one extreme of the an- 

 desitic series of the district, and that next described, an augite-andesite 

 from the Baguio Plateau, cropping out just south of the civic center of 

 Baguio, the other. Megascopically it is a heavy, dark rock, breaking 

 with a conehoidal fracture with a metallic ring. Small phenocrysts are 

 seen in the groundmass, which can not be identified. It weathers on 

 the surface to a brown clayey soil and decomposition has taken place 



