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University of California. 



[Vol. i. 



metrical sections. This plagioclase is undoubtedly albite. Quartz 

 is wholly absent in this facies of the rock. 



The brown mica is in thin scales, often collected into wisps 

 and tufted aggregates. It has a bright chestnut-brown color, with a 

 strong absorption parallel with the cleavage. Cleavage flakes show 

 a biaxial figure with a very small axial angle, the center of the 

 cross barely opening. 



Garnets are thickly scattered through the slide as inclusions in 

 the albite and glaucophane. They rarely exceed o. I mm. in diame- 

 ter, and are usually much smaller. They have a very faint rose 

 tinge, and when one can be found occupying the full thickness of 

 the section, it is isotropic. The index of refraction is very high. 



There are present, also, a few irregular grains of a mineral having 

 a higher index of refraction than the garnets, and of a faint yellowish 

 or gray color. With nicols crossed no marked change is made in 

 the colors of the grains, and the extinctions are not sharp, owing to 

 the diffusion of light that accompanies a high refractive index- 

 Some grains show a biaxial interference figure, with numerous bril- 

 liantly colored rings. The dispersion is p > v and the optical char- 

 acter positive. The mineral is without doubt titanite, and appears 

 to be identical with that described by Palache in the Berkeley rock. 



A portion of the schist was powdered and the minerals sepa- 

 rated by Klein's solution. A large portion of the feldspar fell at 

 about 2.7 sp. gr., leaving the rest suspended. The heavier portion 

 had a slight pink tinge, and when the grains were examined under 

 the microscope, they were seen to contain abundant crystals of 

 garnet, in the form of apparently unmodified rhombic dodecahe- 

 drons. Their color in incident light is a faint pink or wine yellow- 

 The grains of albite are perfectly clear, with a vitreous luster, and at 

 least one perfect cleavage. Many show the striations due to poly- 

 synthetic twinning. A qualitative examination of the pure white 

 feldspar powder, having a specific gravity of about 2.6, showed the 

 presence of silica, soda, and alumina, with a trace of iron, and no 

 lime or magnesia. It is therefore a very pure albite. 



Another facies of the contact zone outcrops near the eastern end 

 of the strip shown on the map, just south of, and below, the summit 

 of the island. This rock, too, has a white granular groundmass, 



