1906.] 



SMITH— PARAGENESIS OF MINERALS. 215 



The basic mica schists have been studied from Camp Meeker, 

 and from the Junction School-house in Sonoma County ; from near 

 Reed's Station on the Tiburon Peninsula ; from Oak Hill near San 

 Jose ; from the Arroyo Hondo at the northern end of Calaveras Val- 

 ley ; and from Hilton Gulch on Oak Ridge, about five miles east of 

 Calaveras Valley. At the two last localities the basic mica schists grade 

 over into pargasite eclogites, and the micaceous mineral appears to 



be margarite. 



VH. Glaucophane Gneiss. 



I. Feldspathic Gneisses. — The feldspathic gneisses of the glauco- 

 phane series are of two different types, the one w^ith abundant 

 orthoclase, and the other with albite as the dominant mineral. 

 Neither type forms independent rock-masses, but both occur as 

 bands in the ordinary glaucophane schists. 



Orthoclase gneiss is known from but two places in the glauco- 

 phane rocks. The best example is that from a locality near Melitta 

 in Sonoma County,- California. This rock, which was found only 

 in float, near a glaucophane schist outcrop, is massive and banded, 

 with long prisms of glaucophane and actinolite in a groundmass of 

 orthoclase and quartz. Small dodekahedrons of pink garnet and 

 thin plates of muscovite are visible in the hand specimen. Thin 

 slides show also abundant titanite in perfect rhombic sections. The 

 glaucophane appears to have been formed after the actinolite, for it 

 replaces the latter around the edges of the crystals. Part of the 

 actinolite has a bluish color, suggesting that it may be carinthine. 

 The glaucophane in this rock has the normal orientation of the axes 

 of elasticity, but has an extremely narrow angle of the optical axes. 

 Some of the bands are composed entirely of quartz with innumerable 

 minute crystals of pink garnet and a few radial tufts of glaucophane. 

 This rock was probably made put of an arkose, for no normal sedi- 

 ments could have the chemical nature necessary for its genesis, and 

 it is hardly likely that an igneous rock would be interbanded with 

 siliceous layers. It may, however, have been made from thin dykes 

 of a granitic nature that were intrusive in the siliceous sediments. 



Becker^ has described from Sulphur Bank in Colusa County 

 (No. 31, Sulphur Bank), a rock similar to that from MeHtta. The 



' Mon. XIII.. U. S. Geol. Survey, p. 102. 



PROC. AMER. PHIL. SOC, XLV. 183N, PRINTED JANirARY 9, I907. 



