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University of California. 



[Vol. 3. 



form. The orthoclase on the contrary forms a cement inclosing, 

 with the possible exception of quartz, all the other minerals of 

 the rock. The basal reflections, mottled by the inclusions, are 

 continuous over areas about 2 cm. in diameter. These areas are 

 apparently not bounded by crystallography; planes, and the 

 inclusions occur in greater quantity than the inclosing feldspar. 

 In these respects the habit of the orthoclase is different from that 

 of the phenocrysts in typical porphyritic granites. 



The microscope reveals the presence of accessory magnetite, 

 apatite, and zircon, which present no unusual characters. A few 

 grains of epidote are seen, which appear to be original. 



The hornblende, which is unaltered, is of the deep green 

 pleochroic variety that is usually found in quartziferous rocks. 

 The biotite is generally of a deep greenish brown, though in some 

 cases it has become grass-green on the edges, without notable 

 change in strength of double refraction. Cleavage flakes 

 examined in convergent light show a distinct separation of the 

 optic axes. 



The plagioclase feldspar, as optically determined, is mainly 

 andesine-oligoclase, but zonal banding is always present, and 

 the outer shells often belong to acid oligoclase. The alkali- 

 feldspar, which is in somewhat smaller amount than the plagio- 

 clase, always occurs inter stitially. 



The quartz is about equal to the orthoclase in amount. While 

 mainly in the form of allotriomorphic grains, it also occurs in 

 mierographic intergrowth with the plagioclase feldspar. 



The period of crystallization for the quartz would thus appear 

 to overlap the final stage in the growth of the plagioclase, and to 

 be anterior to the solidification of the orthoclase, although only 

 one instance of the inclusion of quartz in orthoclase was observed. 

 The order of crystallization is in other respects normal. 



The alteration suffered by the minerals has been but slight; 

 it consists of an incipient kaolinization of the feldspars, and the 

 change noted above in the color of the biotite. The rock, how- 

 ever, breaks up readily under the hammer, and the tendency for 

 the grains to break apart causes difficulty in the preparation of 

 slides. 



The classification of the rock, without chemical analysis, is 



