214 SMITH— PARAGENESIS OF MINERALS. [Octobers, 



Pargasite schists have been studied only from the Arroyo Hondo 

 near the north end of Calaveras Valley ; and from Hilton Gulch 

 on Oak Ridge, about four miles east of Calaveras Valley. At the 

 latter place carinthine is even more abundant in the rocks than 

 pargasite. At both localities the pargasite schist grades over into 

 pargasite eclogite. 



VI. Mica Schists. 



There are two distinct types of mica schists in the glaucophane 

 rocks of California, one associated with acid sediments, altered 

 quartzites or cherts, and the other associated with basic schists, 

 probably made out of diabases or diabase tuffs. 



The acid schists are interbedded with layers rich in quartz, and 

 probably represent clay-shale layers in original siliceous sediments. 

 The mica in them is chiefly muscovite, although biotite sometimes 

 occurs in considerable quantities. Garnet is almost invariably present 

 in this type, and epidote almost never. No pyroxenes of any sort 

 are found in them, and actinolite but rarely. 



The basic mica schists are associated with eclogites and green- 

 stones, and have no quartz. They are composed of paragonite or 

 margarite, glaucophane, epidote, pargasite and carinthine. Where 

 garnet is abundant in them they grade over into eclogite, and where 

 garnet is lacking, and where mica is less abundant they grade over 

 into greenstones. Neither the acid nor the basic mica schists make 

 up independent rock-masses, but occur as bands in quartz glauco- 

 phane schists and in eclogites. 



No chemical analyses have yet been made of either type, but 

 slides have been studied of these rocks from many localities. The 

 acid schists have been studied from Pine Flat, and the Junction 

 School-house near Healdsburg in Sonoma County ; from the Tiburon 

 Peninsula, about one and a half miles north of Tiburon Ferry ; from 

 Belmont Hill, one mile southwest of Belmont ; from Oak Hill near 

 San Jose ; from the Arroyo Hondo at the northern end of Calaveras 

 Valley ; from near Cayucas in San Luis Obispo County ; and from a 

 localitv three miles west of Redwood, and a half mile southeast of 

 the Hopkins reservoir. Biotite occurs in these as an abundant con- 

 stituent only in the rock from near the Hopkins reservoir, and in 

 that from the Tiburon Peninsula. 



