182 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY, 
[BULL. 168. 
P. Hypersthene-andesite, 1 mile west of summit on Bidwell's road, 
Butte County. Rich in small phenocrysts of plagioclase and pyroxene, 
mostly hypersthene, in a groundmass of the same minerals, with magne- 
tite, and probably some amorphous matter. Analysis by W. F. Hille- 
brand, record No. 410. 
Q. Hypersthene-andesite, old crater at head of Mill Creek. Contains 
small phenocrysts of plagioclase and hypersthene, in a groundmass of 
plagioclase, pyroxene, magnetite, etc. Some greenish pseudomorphs 
suggest former olivine. Analysis by T. M. Chatard, record No. 409. 
R. Hypersthene-andesite, 2 miles south of Suppans Mountain, 
Tehama County. Abundant plagioclase and hypersthene, with traces 
of hornblende, in a microlitic groundmass. Analysis by Hillebrand, 
No. 672. 
S. Secretion in R. Composed chiefly of plagioclase and hypersthene, 
with some quartz and amorphous matter. Analysis by Hillebrand, 
No. 673. 
T. Hypersthene-andesite, westb ase of Suppans Mountain, near Las- 
sen Peak, Tehama County. Contains numerous microscopic crystals of 
plagioclase and hypersthene, in a microlitic groundmass. Analysis by 
Hillebrand, No. 676. 
Rocks dried at 100° to 110° before analysis. 
p. 
Q. 
Pv. 
s. 
T. 
Si0 2 .. 
55.20 
18.68 
3.14 
4.42 
4.59 
8.02 
3.66 
1.01 
.51 
.92 
.24 
.14 
.02 
.03 
none 
57.11 
17.78 
3.54 
2.74 
3.41 
7.21 
3.81 
1.86 
.98 
.95 
.26 
.33 
trace ? 
.03 
63.47 
16.75 
2.15 
2.75 
3.04 
5.72 
3.94 
1.62 
.55 
.37 
.13 
.09 
.04 
.04 
trace 
57.04 
19.11 
4.37 
2.48' 
3.94 
7.34 
3.48 
1.16 
1.09 
.47 
.08 
.12 
.02 
trace ? 
trace 
58.08 
18.37 
2.92 
3.38 
3.35 
7.05 
3.66 
1.33 
1.09 
.44 
.16 
.13 
.02 
.03 
trace 
A1 2 3 
Fe 2 3 
FeO 
MgO 
CaO 
Na 2 
K 2 
H 2 
Ti0 2 
P 2 5 
MnO 
SrO 
BaO 
Li 2 
100. 58 
100. 01 
100. 66 
100. 70 
100. 01 
