216 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. [no. 228. 
U. Hypersthene-andesite, 1 mile southwest of Thumb, head of Bailey 
Creek, near Lassen Peak. Tonalose. Abundant but inconspicuous 
plagioclase and hypersthene, in a microlitic groundmass containing 
many small crystals of plagioclase. Analysis by W. F. Hillebrand, 
record No. 675. 
V. Hypersthene-andesite, west summit of Crater Peak, Shasta 
County. Yellowstonose. Microphenocrysts of feldspar and hyper- 
sthene in a groundmass consisting largely of the same minerals, with 
some amorphous matter. Analysis by Hillebrand, No. 679. 
W. Hypersthene-andesite, north slope of Crater Peak. Tonalose. 
Phenocrysts of plagioclase and hypersthene in a groundmass containing 
much dark amorphous matter. Analysis by Hillebrand, No. 680. 
X. Secretion in W. Hessose. Composed chiefly of plagioclase, 
hypersthene, and a globulitic base, Analysis by Hillebrand, No. 681. 
Y. Andesitic tuff, Stillwater Creek, 8 miles northeast of Redding. 
Contains plagioclase, hornblende, rare hypersthene, magnetite, and 
glass. Fragments of andesite are inclosed. Analysis by W. H. Mel- 
ville, record No. 1346. Described by Diller in Bull. 150, p. 211. 
P. R. C. 79. 
Rocks dried at 100° to 110° before analysis. 
Si0 2 . 
A1 2 3 
Fe 2 3 
FeO. 
MgO 
CaO. 
Na 2 
K 2 0. 
H 2 0. 
Ti0 2 _ 
PA- 
Cr 2 :i 
MnO 
SrO . 
BaO. 
LLO 
59. 84 
16.81 
1.88 
3.60 
3. 85 
6.30 
3. 63 
2.13 
1.04 
.57 
.19 
trace? 
.14 
.02 
.07 
trace 
100. 07 
68.12 
16.24 
1.26 
2.08 
1.35 
3.80 
3.89 
2.54 
. .40 
.25 
.14 
none 
.10 
.02 
.09 
trace 
100. 28 
W. 
61.17 
17.74 
1.78 
3.51 
2.76 
5.90 
3.79 
1.71 
.83 
.45 
.14 
none 
.12 
.04 
.06 
trace 
100. 00 
53.85 
18. 53 
1.96 
5.30 
5.88 
9.66 
2.98 
.74 
.45 
.50 
.05 
trace 
.12 
.04 
.03 
trace 
100. 09 
69.51 
15.61 
.56 
1.27 
.61 
2.80 
3.43 
2.81 
3.63 
trace 
100. 23 
