i9o6] SMITH— PARAGENESIS OF MINERALS. 231 



quartz diorite. Even the quartz, which makes up about one-third of 

 the rock, is secondary, for there could not have been any such quan- 

 tity of free quartz in the original rock with only 66 per cent, of 

 silica. The original minerals were probably oligoclase, hornblende, 

 and quartz, and the addition of 4 per cent, water has lowered the 

 silica from 68 per cent, to 65.9 per cent. The original hornblende 

 was probably titaniferous, for numerous small aggregates of titanite 

 are visible in the slides. The original rock was probably a quartz 

 diorite similar to that of Oak Ridge described above, but with the 

 readjustment complete. A chemical analysis of this rock by Mr. W. 

 O. Clark, assistant in geology at Stanford University, gave the 

 following results : 



Lawsonite Diorite with 



Gneiss. Crossite. 



I. II. 



Si02 65.91 61.55 



AI0O3 1 1.62 17.28 



Fe203 2.21 1.49 



FeO 5.30 3.50 



MgO 1.92 3.00 



CaO 5.89 3.12 



NaaO 1.95 8.47 



K2O 0.04 0.07 



H2O (100° C.) 0.28 0.12 



H2O ' (above 110° C.) 4.38 1.21 



MnO trace trace 



Ti02 0.17 0.28 



Total 99.67 100.12 



I. Lawsonite gneiss, three miles west of Redwood, W. O. Clark, analyst. 



II. Quartz diorite with some secondary crossite and lawsonite, Oak Ridge, 

 five miles east of Calaveras Valley, W. O. Clark, analyst. 



A comparison of these two analyses shows the lawsonite gneiss 

 to have been more like an ordinary quartz diorite in composition ; 

 while the diorite with secondary crossite is somewhat allied chem- 

 ically to the soda syenite porphyries. 



About one mile soutl of the mouth of Coyote Canon, Santa Clara 

 County, is a mass composed of glaucophane schist, lawsonite-garnet- 

 glaucophane gneiss, and lawsonite-glaucophane schist. In the latter 

 phase both lawsonite and glaucophane are perfectly fresh, but there 

 is a large amount of talc formed, which was clearly not made at the 



PROC. AMER. PHII,. SOC. , XLV. 183O, PRINTED JANUARY 14, I907. 



