212 SMITH-PARAGENESIS OF MINERALS. [Octobers. 



such a rock from Sulphur Bank, under the name of zoisite- 

 glaucophane schist, but, as shown above, the so-called zoisite is 

 probably a pale epidote. Besides this mineral Becker noted abun- 

 dant glaucophane, and a little albite, white mica, quartz, and titanite. 

 The analysis given of this rock by Becker is quoted below. A similar 

 epidote-glaucophane schist has been described by Washington^ from 

 Winston's Bridge, near Roseburg, Oregon. The analysis given by 

 Washington is quoted below, along with an analysis of an epidote- 

 glaucophane schist from Syra in the Grecian Archipelago. 



These rocks all agree in the abundance of epidote, the occasional 

 presence of zoisite, and the absence of garnet. Chemically they agree 

 exactly with the garnet-glaucophane schists, and with the pseudo- 

 diabases and fourchite, and they were all doubtless formed from 

 metabasalt. 



The chief occurrences in California of epidote-glaucophane schist 

 that have been studied in detail are : Sulphur Bank in Colusa County ; 

 Junction School-house near Healdsburg ; North Berkeley ; Arroyo 

 Hondo in Calaveras Valley, San Juan Mine at Oak Hill near San 

 Jose. 



3. Glaitcophane-lawsonite schists. — Associated with the ordinary 

 types of schists at a few places in California are found rocks com- 

 posed almost exclusively of lawsonite and glaucophane. The glau- 

 cophane in fine needles forms a compact grouridmass in which are 

 imbedded rectangular prisms of lawsonite. Sphene is scattered 

 through the mass in irregular patches. Neither garnets nor epidotes 

 occur in any quantity in this type of schists. Talc is a common con- 

 stituent of the lawsonite-glaucophane schists, and is apparently not a 

 product of weathering, but was made at the same time with the 

 other minerals. The original rock was either a basic igneous rock 

 rich in lime and magnesia, or a basic tuff. When glaucophane was 

 formed out of primary hornblende or pyroxene the excess of silicate 

 of magnesia crystallized out as talc. No analyses have been made 

 of the lawsonite-glaucophane schists, but estimates, based on a 

 study of numerous thin sections, show them to have the constitution 

 of diabases or diabase tuffs. They have been studied in detail at 

 Guerneville ; on the Hellman ranch three miles west of Redwood ; 



^ Amer. Jour. Set., IV. Ser., Vol. XL, p. 53. 



