ransome.i Geology of Angel Island. 235 



Inclusions of the schist are frequent in certain portions of the 

 serpentine, especially in the small area just referred to, where sev- 

 eral occur of large size. Smaller fragments are also visible in the 

 cliff section at the extreme southern end of the main dyke. 



Although the whole area between the various outcrops of ser- 

 pentine just referred to near the south end of the dyke is mapped as 

 metamorphic rock, yet it is not all of the character just described. 

 Away from the immediate contact with the serpentine, it is a green- 

 ish gray, schistose rock, with a fine granular texture and vitreous, 

 rather greasy, lustre. When exposed on the beach it is seen to 

 form thick beds made up of numerous thin lamina,-, parallel with the 

 planes of schistosity. The dip and strike of these beds, and, in fact, 

 their general appearance at a little distance, correspond closely with 

 that of the thinly laminated sandstone to the east of the serpentine. 

 Under the microscope, the rock shows the usual finely crystalline 

 mosaic, in which both feldspar and quartz occur; the former, how. 

 ever, seems to predominate. Scattered through this matrix are a 

 few crystals and bunches of glaucophane. With a high power, a 

 certain cloudiness in the groundmass resolves itself into innumer- 

 able crystal grains and needles. The latter in general show the 

 pleochroism and extinctions of a light green actinolite, and give to 

 the rock its slight greenish tinge. 



The eastern side of the serpentinized dyke shows, as has been 

 stated, far less evidence of metamorphic action than does the west- 

 ern. Nevertheless, at both ends of the dyke, where it is exposed 

 through wave action, alteration can readily be made out, and the 

 probabilities are that a zone of contact metamorphic rock borders 

 the eastern edge also, but is concealed by the soil. 



At the southern extremity of the dyke, the rock immediately 

 adjoining the serpentine on the east is a light-greenish schist, with 

 fine granular texture and oil)' lustre, standing in nearly vertical lay- 

 ers. These layers or laminse appear to represent the original bed- 

 ding planes of the sandstone into which the schist gradually passes, 

 the schistosity having been developed parallel with them. Under 

 the microscope, it shows a thick felt of prisms and needles of pale 

 greenish-white actinolite imbedded in a feldspathic base, the grains 

 of which possess shadowy boundaries and hazy, uncertain extinc- 



