220 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. 
[xo. 228. 
3. PLUMAS COUNTY. 
Other rocks from this county are described under the heading of the 
Lassen Peak area. The following rocks, with two exceptions, were 
collected by H. W. Turner, who supplies the descriptions: 
A. Granite, dike in serpentine, south slope of Grizzly Hill. Near 
alashose. Described by Turner in Amer. Geologist, vol. 17, p. 375. 
Contains quartz, albite, and muscovite. Analysis by H. N. Stokes, 
record No. 1562. P. R. C. 757. 
B. Metarhyolite, near Tower Rock, Grizzly Mountains. Toscanose. 
Described by Turner in 11th Ann., p. 111. Contains porphyrinic 
quartz, feldspar, and p}^rite, in a fine groundmass. Analysis by W. 
F. Hillebrand, record No. 1273. P. R. C. 711. 
C. Metarhyolite, near Greenville. Yukonose. Collected by Diller, 
who finds phenocrysts of quartz in a groundmass chiefly of quartz and 
feldspar. Analysis by Hillebrand, record No. 1158. 
D. Granodiorite, southwest base of Mount Ingalls. Yellow stonose. 
Description supplied by Turner. Contains plagioclase, quartz, ortho- 
clase, brown mica, green hornblende, iron oxide, and a little apatite, 
sphene, and epidote. Analysis by Hillebrand, record No. 1156. 
P. R. C, 727. 
E. Granodiorite, Spanish Peak. Tonalose. Description supplied by 
Turner. Contains plagioclase, quartz, orthoclase, biotite, hornblende, 
iron ore, and apatite; also abundant secondary epidote and chlorite. 
Analysis by Stokes, record No. 1562. P. R. C. 756. 
Si0 2 . 
A1 2 0„ 
Fe 2 3 
FeO 
MgO 
CaO 
Na,0 
K 2 
H 2 OatlOO°.... 
H 2 above 100 c 
Ti0 2 
MnO. 
SrO. 
BaO. 
Li 2 
co 2 . 
so 3 . 
CI... 
F... 
FeS, 
76.00 
14.88 
.65 
.10 
.06 
.19 
3.52 
2.77 
.20 
1.42 
.04 
.11 
trace 
trace 
trace 
trace 
trace 
99.94 
73.25 
13.25 
1.74 
.28 
2.23 
2.69 
3.79 
.07 
1.03 
trace 
trace 
trace 
trace? 
trace 
trace 
1.05 
58 
99.96 
C. 
72.77 
13.00 
1.28 
2.65 
.67 
2.47 
4.95 
.34 
.07 
1.16 
.22 
.04 
.08 
trace 
trace 
trace 
.47 
100. 17 
i). 
67.33 
.36 
.11 
.09 
trace 
.08 
trace 
100. 18 
59. 68 
17.09 1 
2.85 
2.75 
3.54: 
6.62 
3.87 
1.31 
.15 
1.00 
.65 
.25 
tra 
tra 
.04 
trace 
.2C; 
to 
100.' 
