IGNEOUS AND CRYSTALLINE ROCKS. 
211 
1. RHYOLIT 
A. Rhyolite, a short distance northwest of Willow Lake, near the 
Geyser, Plumas County. Alaskose. A light-gray rock with occa- 
sional phenocrysts of quartz and feldspar in a granular groundmass of 
the same materials. Analysis by W. F. Hillebrand, record No. 414. 
B. Rhyolite, 2 miles northwest of Deer Creek Meadows, Tehama 
County. Tehamose. Shows many small crystals of quartz, feldspar, 
and biotite in a spherulitic groundmass. Analysis by Hillebrand, 
No. 415. 
C. Rhyolite, Slate Creek, west of Deer Creek Meadows. Tehamose. 
Composed wholly of spherulites, some of which include crystals of 
feldspar or biotite. Analysis by Hillebrand, No. 410. 
D. Rhyolite, summit of Mount Stover, Plumas County. Toscanose. 
Composed almost wholly of spherulites, with a few crystals of feldspar 
and hornblende. Analysis by Hillebrand, No. 417. 
E. Rhyolite, near Slate Creek, west of Deer Creek Meadows. Tos- 
catio.se. A pearlite, composed chiefly of little glass balls, with a few 
spherulites, and crystals of feldspar and biotite. Analysis b}^ Hille- 
brand, No. 418. 
F. Rhyolite, 1£ miles northeast of Clipper Mills, on tramway to 
Rock Creek, Shasta County. Tehamose. A spherulitic rock contain- 
ing a few microscopic particles of feldspar and hornblende. Analysis 
by Hillebrand, No. 678. 
G. Rhyolite-tuff, divide between the west fork of Willards Creek 
and the stage road, in Lassen County. Elevation, 5,800 feet. Com- 
posed almost wholly of fine angular particles of clear glass. Analysis 
by George Steiger, record No. 1427. 
Materials for A to F dried at 110° previous to analysis. 
A. 
B. 
C. 
D. 
E. 
F. 
G. 
Si0 2 
A1 2 3 
Fe 2 3 
74.24 
14. 50 
1.27 
.67 
.25 
.11 
3. 00 
3.66 
74.65 
14. 11 
1.08 
.29 
.20 
.80 
2.81 
4.59 
73.62 
14.24 
. 93 
.67 
.33 
1.07 
3.25 
4.28 
72.40 
14.81 
.81 
.88 
.47 
1.114 
3.91 
3.90 
73.64 
13. 44 
.60 
.74 
.26 
1 . 26 
3.51 
4. 50 
74. 60 
13.41 
1.28 
.30 
.26 
1.08 
3.38 
4. 50 
70. 01 
12.61 
1.47 
FeO 
.50 
M^O 
.72 
pa( ) 
1.06 
Na 2 < ) 
1.94 
K 2 
5.12 
H 2 Oatl00° 
2.37 
H 2 above 100° 
Ti0 2 
2.04 
.20 
.07 
.06 
trace 
.is 
none 
. 03 
1.40 
.21 
trace 
.11 
trace 
.08 
none 
1. 29 
.21 
.02 
.08 
trace 
.10 
none 
.59 
.18 
.03 
.07 
.04 
.10 
trace 
1.91) 
.11 
.06 
.06 
.02 
.11 
trace 
.85 
.16 
.03 
.06 
none 
.11 
trace 
4.68 
PA 
.04 
MnO 
SrO 
BaO 
Li 2 
trace 
so 3 
100. 28 
100.33 
100.09 
100. 13 
100. 30 
100. 02 
100. 52 
