IO 



University of California. 



[Vol. i. 



sketch of a slab in the quarry showing this parallelism or stream-like 

 distribution of the orthoclase phenocrysts in the ground-mass. 

 The appearance is very suggestive of a flow structure in a viscous 

 mass slowly crystallizing. 



Figure i. — Diagram to illustrate the parallelism of the orthoclase phenocrysts 

 in the Santa Lucia granite, at the old granite quarry, Carmelo 

 Cove. 



The basal cleavages of the phenocrysts are very lustrous, but 

 they all show in a marked degree the appearance known as " luster 

 mottling," due to the inclusions of foreign minerals in the crystals. 

 These inclusions were found on microscopic investigation to com- 

 prise crystals of plagioclase, orthoclase, quartz, biotite, and musco- 

 vite. The first four of these are very abundantly represented. 

 The muscovite is more sparing. In some cases these inclusions 

 are so abundant as to constitute, on an estimate, as much as 20 per 

 cent, of the phenocryst. With the exception possibly of the micas, 

 these inclusions are arranged in definite planes and lie parallel to 

 either the clinopinacoid or to the prism faces. While the pheno- 

 cryst host is usually quite fresh and glassy, the included feldspars 

 are frequently cloudy, owing to partial decomposition, and the regu- 

 lar arrangement of these cloudy inclusions gives the large ortho- 

 clases a distinct zonal appearance. The inclusions are in the sec- 

 tions examined very commonly about .25 to 1 mm. in length, while 



