1895.]. Petrography. 41 
PETROGRAPHY:' 
The Serpentines of San Francisco.—The serpentine of the 
Protero, a district within the limits of the city of San Francisco, is an 
eruptive rock intrusive in sandstone. .It was originally a lherzolite, 
which by the usual processes of alteration has been changed to ser- 
pentine. Two varieties of the rock are noticed by Palache.? One is a 
massive form, while the other is slickensided along so many planes 
close together that the rock has became schistose. Between the slick- 
ensided surfaces are often spheroidal masses of the massive rock. 
The massive serpentine is of the usual character. It consists now of a 
felt of serpentine fibres in which are imbedded numerous crystal-like 
areas of enstatite and diallage, and grains of olivine, magnetite and 
chromite. The crystal-like particles of the pyroxenes are remnants 
of larger grains that were shattered by dynamic action. The pyrox- 
enes and the olivine have yielded the serpentine. Intrusive into the 
serpentine is a hypersthene diabase, composed of labradorite, mono- 
clinic and orthorhombic pyroxenes and green hornblende, supposed to 
be derived from the pyroxene. Its structure is ophitic. A second 
variety of the rock consists essentially of plagioclase and hornblende. 
Portions of it are schistose. Its structure is sometimes granitic and 
sometimes ophitic, and in the latter case it contains small quantities of 
pyroxene. Hence it is regarded as an altered form of the diabase. 
An analysis of the hornblende variety follows : 
SiO, Al,O, Fe,O, FeO MnO CaO MgO K,O Na,O PO TiO, H,O Total 
47.41 16.03 2.66 7.05 tr 12.33 5.81 4.47 tr 1.29 9.19—99. 24 
Density = 2.96. i 
The Blue Hornblende in the California Schists.—In many 
of the schists of the Coast Range, Cal., isa blue amphibole that has 
for some years past gone under the name of glaucophane. Palache* 
has recently found it in large quantities and in well developed column- 
ar crystals in aschist-boulder near Berkely. The matrix of the schist 
is a granular aggregate of clear, fresh albite, containing numerous 
liquid and solid inclusions. The latter consist largely of small grains 
1 Edited by Dr. W. S. Bayley, Colby University, Waterville, Maine. — 
2 Bull. Geol. Dept. Univ. of Cal., Vol. 1, p. 161. 
Tb, Vol. 1, p. 181. 
