108 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. [bull. If 
U. Hornblende-mica-andesite, Crescent Hill. Analysis by Whi 
field, No. 432, hitherto unpublished. Reported b}^ Iddings as coi 
taining oligoclase-andesine, biotite, and subordinate decompose 
hornblende, in a groundmass of feldspar and quartz, with a littl 
magnetite and biotite. 
V. Hornblende-andesite, Tower Creek. Analysis by Gooch, Nc 
117, hitherto unpublished. Reported by Iddings as containing plagic 
clase, hornblende, and a little augite. 
W. P}^roxene-andesite, Agate Creek. Analysis by Whitfield, Nc 
432, hitherto unpublished. Reported by Iddings as containing augite 
ivypersthene, labradorite, and magnetite, in a glassy, microliti 
groundmass. 
X. Rhyolitic perlite, described by Iddings, Bull. 150, p. 158 
Analysis by H. N. Stokes, No. 1314, hitherto unpublished. From i 
bluff opposite the Midway Geyser Basin. Reported by Iddings a 
containing quartz, sanidine, plagioclase, and rarely augite and mag 
netite, with microscopic zircon and apatite, in a glassy groundmass 
P. R. C. 61. 
Si0 2 . 
A1 2 3 
Fe 2 3 
FeO. 
MgO 
CaO. 
Na 2 
K 2 0. 
H 2 0. 
TiCV 
PA- 
MnO 
Li 2 
so 3 . 
CI... 
co 2 . 
64.61 
18.62 
2.78 
.95 
.85 
4.20 
4.37 
2.36 
.93 
none 
.30 
trace 
.01 
trace 
trace 
.25 
100.23 
61.56 
14.73 
4.47 
1.23 
3.57 
4.87 
5.10 
2.24 
1.42 
.87 
.04 
.34 
100. 44 
W. 
61.45 
15.07 
4.46 
1.18 
3.02 
5. 37 
4.00 
1.22 
1.23 
2.80 
trace 
none 
.05 
.29 
100.14 
73.84 
12.47 
.32 
.90 
.25 
1.08 
2.88 
5.38 
9. 7fi 
trace 
99.88 
