•LARKE.] 
IGNEOUS AND CRYSTALLINE ROCKS. 
119 
P. Pitchstone, or rhyolite-dacite obsidian, Butte Phenocrysts of 
andesine, quartz, and orthoclase in a glassy base. 
Q. Rhyolite, Hyde Park dike, Butte district. Contains sanidine, 
quartz, plagioclase, and biotite in a groundmass of quartz and feldspar. 
R. Rhyolite, top of Red Mountain, Rimini. Quarts and feldspar 
phenocrysts in a groundmass of the same minerals. 
S. Quartz-porphyry, Modoc mine, Butte district. Contains quartz, 
orthoclase, and plagioclase in a groundmass of quartz and feldspar. 
A few small biotites are present. Feldspar partly altered to sericite. 
T. Andesite- porphyry, Hiawatha Creek, above basin. Contains pla- 
gioclase, orthoclase, and augite. 
U. Andesite-porphyry, Zosel mining district, near Da^ylight. Some- 
what altered. Contains augite, andesine, and olivine in a groundmass 
of plagioclase, augite and iron oxide. Ferromagnesian minerals 
altered to serpentine. 
Analysis S by Hillebrand, record No. 1692. P, Q, R, T, and U by 
Stokes, record Nos. 1686, 1787. 
P. 
Q. 
R. 
s. 
T. 
U. 
Si0 2 
67.55 
15.68 
.98 
1.02 
1.11 
2.51 
4.15 
2.86 
.38 
2.76 
.34 
.12 
none 
trace 
.03 
.11 
none 
none 
none 
74. 34 
12.97 
.75 
.54 
.86 
.85 
2.49 
4.72 
1.03 
1.11 
.18 
.07 
.05 
trace 
trace 
.07 
trace 
none 
.03 
75.30 
11.95 
^ 2.17 
.05 
.62 
3.09 
4.96 
.36 
.61 
.17 
trace 
69.95 
15.14 
.38 
.83 
.56 
1.45 
2.70 
6.36 
.40 
.91 
.24 
.10 
.02 
.08 
.02 
.13 
trace 
.37 
62.53 
19.01 
1.96 
1.44 
1.29 
5.17 
3.45 
3.30 
.21 
.45 
.65 
.17 
54.61 
15.23 
3.51 
4.80 
4.69 
7.41 
1.46 
2.70 
.32 
2.47 
.86 
.35 
none 
.09 
.04 
.11 
trace 
1.46 
none 
A1 2 3 
Fe 2 3 
FeO 
MgO 
CaO 
Na 2 
K 2 
H 2 OatllO°... 
H 2 above 110° 
Ti0 2 
P 2 5 
Zr0 2 
MnO 
trace 
none 
trace 
trace 
none 
.44 
.03 
.04 
.13 
trace 
none 
none 
SrO 
BaO. 
Li 2 
C0 2 
SO, 
FeS 2 
a. 39 
undet. 
.03 
CI 
.05 
none 
trace 
none 
Cu 
Organic matter 
.45 
99.65 
100. 06 
100. 17 
100. 06 
99.83 
100. 11 
a Other sulphides than pyrite present. 
