178 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. 
[bull. 168. 
1st. rhyolites. 
A. Rhyolite, a short distance northwest of Willow Lake, near the 
Geyser, Plumas County. A light-gray rock with occasional pheno- 
crysts 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. 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. Composed 
wholly of spherulites, some of which include crystals of feldspar or 
biotite. Analysis by Hillebrand, No. 416. 
D. Rhyolite, summit of Mount Stover, Plumas County. Composed 
almost wholly of spherulites, with a few crystals of feldspar and horn- 
blende. Analysis by Hillebrand, No. 417. 
E. Rhyolite, near Slate Creek, west of Deer Creek Meadows. A 
pearlite, composed chiefly of little glass balls, with a few spherulites, 
and crystals of feldspar and biotite. Analysis by Hillebrand, No. 418. 
F. Rhyolite, 1^ miles northeast of Clipper Mills, on tramway to 
Rock Creek, Shasta County. A spherulitic rock containing a few 
microscopic particles of feldspar and hornblende. Analysis by Hille- 
brand, 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 
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 
1.94 
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 
.50 
.72 
1.06 
1.94 
5.12 
2.37 
4.68 
ALO a *...*- 
Fe 2 3 
FeO 
MgO 
CaO 
Na 2 
K 2 
H 2 at 100° 
H 2 above 100° 
TiO a 
2.04 
.20 
.07 
.06 
trace 
.18 
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 
1.99 
.11 
.06 
.06 
.02 
.11 
trace 
.85 
.16 
.03 
.06 
none 
.11 
trace 
P„(X 
.04 
trace 
MnO 
SrO 
BaO 
Li 2 
SO. 
100. 28 
100. 33 
100. 09 
100. 13 
100. 30 
100. 02 
100. 52 
