180 
ANALYSES OF ROCKS, TJ. S. GEOLOGICAL SURVEY. 
[bull. 168. 
F. Dacite, east end of Chaos, northwest base of Lassen Peak. The 
youngest dacite of the region. Contains quartz, feldspar, biotite, and 
hornblende, embedded in a clear pumiceous glass. Analysis by W. F. 
Hillebrand, record No. 670. Described by Diller in Bull. 150, p. 218. 
G. Secretion in F. Consists chiefly of plagioclase and hornblende, 
with some olivine and clear glass. Analysis by Hillebrand, No. 671. 
H. Dacite (?), west side of old crater rim near the Thumb, at the 
head of Mill Creek, Shasta County. Shows phenocrysts of hornblende, 
plagioclase, and pyroxene, and apparently of quartz, in a gray, micro- 
litic groundmass. Analysis by Hillebrand, No. 674. 
I. Streaked dacite, falls of south fork of Bear Creek, Shasta County. 
Contains plagioclase with a little sanidine, hornblende, quartz, mag- 
netite, some pyroxene inclusions, and glass base. Analysis by R. B. 
Riggs, record No. 524. P. R. C. 80. Described by Diller in Bull. 
150, p. 213. 
J. Dacite-tuff, Rice's quarry, 6 miles southeast of Paskenta, Tehama 
County. Clear glass, with fragments of quartz, feldspar, and horn- 
blende. Analysis by George Steiger, record No. 1427. 
F. 
G. 
H. 
I. 
68.10 
15. 50 
3.20 
none 
.10 
3.02 
4.20 
3.13 
J. 
65.78 
14.87 
1.27 
1.00 
1.89 
2.41 
2.58 
2.71 
2.87 
4.32 
Si0 2 
68.72 
15.15 
1.16 
1.76 
1.28 
3.30 
4.26 
2.78 
53.35 
19.22 
3.28 
4.48 
4.86 
9.76 
2.89 
.99 
63.81 
17.07 
2.11 
2.15 
2.28 
4.97 
4.08 
1.96 
A1 2 3 
Fe 2 3 
FeO 
MgO 
CaO 
N^O 
K 2 
H 2 at 100° 
H 2 above 100° 
Ti0 2 
.74 
.31 
.09 
.11 
.03 
.07 
trace 
.77 
.56 
.10 
.15 
.03 
trace ? 
trace 
♦ 1.03 
.38 
.10 
.09 
.03 
.04 
trace 
2.72 
.15 
.03 
trace 
trace 
.06 
none 
P„O fi 
.08 
trace 

MnO 
SrO 
BaO 
Li 2 
99.76 
100.44 
100. 10 
100. 21 
99.78 
