106 
ANALYSES OF EOCKS, U. S. GEOLOGICAL SURVEY. 
[BULL. 168. 
L. Trachy tic rhyolite-tuff, Two Ocean Pass. Analysis by Whitfield, 
No. 906, hitherto unpublished. Reported by Iddings as containing 
sanidine, labradorite, biotite, magnetite, and augite, in a somewhat 
altered, glassy groundmass. Also contains fragments of andesite. 
M. Glassy trachyte, approaching rhyolite, Sunset Peak, Bear Gulch. 
Contains phenocrysts of sanidine, plagioclase, and biotite. See Iddings, 
Bull. Phil. Soc. Washington, vol. 12, p. 205; also Mon. XXXII, 
Pt. II. Analysis by L. G. Eakins, record No. 1378. 
N. Altered rhyolite, " Iron Pot," Lower Basin. Collected by W. H. 
Weed. Analysis by Whitfield, No. 546, hitherto unpublished. 
O. Dacite-porphyry, Echo Peak. 
P. Same as O, Mount Holmes. Analyses O and P by Whitfield, 
Nos. 421, 422, hitherto unpublished. Reported by Iddings as con- 
taining plagioclase, probably oligoclase, quartz, little biotite, and 
magnetite. 
Si0 2 .. 
A1 2 3 . 
Fe 2 3 
FeO . 
MgO. 
CaO.. 
K 2 0. 
H 2 0. 
Ti0 2 
PA 
MnO 
BaO. 
Li 2 
SO, . 
61.15 
15.70 
4.31 
1.12 
3. 04 
2.84 
1.54 
2.22 
7.05 
.69 
.75 
trace 
none 
.18 
100. 59 
69.45 
14.92 
3.16 
.23 
.05 
1.19 
3.19 
5.95 
1.69 
.19 
.06 
.07 
.03 
100. 18 
N. 
89.20 
2.39 
1.21 
none 
trace 
trace 
1.11 
.79 
5.09 
none 
none 
.44 
100. 23 
74.51 
14.83 
1.09 
trace 
.47 
.81 
4.38 
2.72 
.92 
none 
trace 
none 
.02 
.24 
99. 99 
69.54 
17.95 
2.50 
.22 
.50 
1.80 
4.30 
1.21 
1.96 
none 
none 
none 
trace 
.37 
100. 35 
