194 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. 
[BULL. 168. 
6. NEVADA CITY AND GRASS VALLEY. 
Rocks of a mining district in Nevada County, described by Lind- 
gren in 17th Ann., Part II, p. 1. 
A. Granodiorite, 1 mile southeast of Nevada City. Contains horn- 
blende, biotite, quartz, plagioclase, orthoclase, magnetite, apatite, 
sphene, and pyrite. Analysis by W. F. Hillebrand, record No. 1478. 
B. Granodiorite, Kate Hayes Hill, Grass Valley. Contains plagio- 
clase, orthoclase, quartz, hornblende, pyrite, magnetite, apatite, sphene, 
and zircon. Analysis by Hillebrand, No. 1478. 
C. Hornblende-porphyrite, Nevada City. Contains feldspar, horn- 
blende, quartz, epidote, sericite, and biotite. Analysis by H. N. 
Stokes, record No. 1531. 
D. Quartz-porphyrite, New Ophir claim, Grass Valley. Contains 
plagioclase, quartz, uralite, epidote, and augite, and hornblende altered 
into chlorite. Analysis by Stokes, No. 1531. 
E. Diabase, near Maryland mine, Grass Valley. Contains feldspar, 
augite, hornblende, ilmenite, pyrrhotite, pyrite, and some chlorite. 
Analysis by Stokes, No. 1522. 
F. Diabase, Grass Valley. Contains feldspar, pyroxene, hornblende, 
ilmenite, pyrrhotite, pyrite, and chlorite, and probably a little quartz. 
Analysis by Stokes, No. 1522. 
A. 
B. 
c. 
D. 
E. 
F. 
Si0 2 
66.65 
16.15 
1.52 
2.36 
1.74 
4.53 
3.40 
2.65 
.18 
.72 
.38 
.10 
63. 85 
15. 84 
1.91 
2.75 
2.07 
4.76 
3.29 
3.08 
.28 
1.65 
.58 
.13 
62.09 
16.69 
1.45 
3.76 
1.93 
6.08 
3.36 
1.84 
.19 
1.47 
.32 
.39 
63.39 
16.58 
1.41 
3.08 
2.15 
4.76 
3.47 
2.79 
.22 
1.87 
.44 
.14 
51.01 
11.89 
1.57 
6.08 
8.87 
10.36 
4.17 
.15 
.24 
2.09 
.98 
.17 
.04 
trace 
53.19 
17.12 
, 4.35 
5.16 
3.98 
9.39 
2.79 
.28 
.17 
1.21 
1.34 
.13 
none 
trace 
A1 2 0, 
Fe 2 0, 
FeO 
MgO 
CaO 
Na 2 
K 2 
H 2 OatllO°... 
H 2 above 110° 
Ti0 2 
P„0. 
Cr 2 3 
MnO 
.10 .07 
trace tra.r.e 
trace 
trace 
SrO 
BaO 
.07 
trace 
.06 
trace 
.10 
.11 
none 
trace 
Li 2 
SO, 
.10 
FeS 2 
.02 
.04 
1.73 
trace 
.94 
CuS (?) 
100. 57 
100. 36 
99.77 
100. 41 
99.35 
100. 05 
