218 SMITH— PARAGENESIS OF MINERALS. [Octobers, 



but grades over into thin bedded acid mica schists. The constituent 

 minerals are quartz, glaucophane, pink garnet, muscovite, actinolite 

 and titanite, sometimes with a httle feldspar. These rocks are 

 undoubtedly siliceous sediments, either quartzite or chert, but every- 

 thing in them is recrystallized, so that it is usually impossible to 

 distinguish the product of the alteration of the quartzite from that 

 of a chert. 



Washington^ has described from Four Mile Creek in Oregon a 

 quartz glaucophane schist or gneiss, consisting of quartz, glauco- 

 phane, pink garnet, muscovite, and a little chlorite. The analysis 

 given by Washington is quoted below. 



A similar rock, but more massive and gneissic, occurs near Pine 

 Flat, Sonoma County, on the Foss road from Calistoga to the 

 Geysers, and near the house of J. Mueller. This locality is about 

 two miles from the Geysers, and four miles from the Eureka mine. 

 The rock is a massive banded gneiss, with abundant quartz, and 

 muscovite, many long prisms of glaucophane, very small pink gar- 

 nets, and a little actinolite. The glaucophane and actinolite are 

 badly shattered, showing that at least a part of the crushing took 

 place after they were formed. 



A similar rock to that from near Pine Flat was studied by Nutter 

 and Barber from the Junction School-house near Healdsburg. 



On the Tiburon Peninsula, a mile and a half northeast of the 

 Tiburon ferry is found a massive quartz gneiss. The rock contains 

 abundant quartz, muscovite and biotite, numerous very small pink 

 garnets, and a little actinolite, and small crystals and aggregates 

 ^f titanite. There are numerous prisms that resemble glaucophane 

 in appearance, but the pleochroism is more intense and the plane of 

 the optical axes transverse, hence the mineral is the variety crossite. 

 All the crystals in the rock are shattered, displaced and healed with 

 secondary silica. Some of the clear glassy minerals may be albite, 

 but none were found giving a biaxial figure. 



Ransome^ has described from Angel Island a quartz glaucophane 

 gneiss very similar to that from the Tiburon Peninsula, and the two 

 localities are not over two miles apart. But the Angel Island 



^Amcr. Jour. Set., IV. Ser.. Vol. XI. (1901), p. 53- 

 '^Bull. Dept. Geol. Univ. of California, Vol. I., p. 215. 



