130 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. 
[BULL. 168. 
H. Feldspar-porphyry, dike below Castle. Contains orthoclase, less 
plagioclase, hornblende, biotite partly altered to chlorite, sometimes 
allanite, and occasional iron ore, apatite, and zircon. P. R. C. 555. 
I. Rhyolitic tuff, near forks of Checkerboard Creek. Contains 
fragments of shale, quartz, plagioclase, sanidine, and hornblende, in a 
brownish material carrying pumiceous glass. Much decomposed, with 
formation of kaolin. P. R. C. 562. 
J. Syenitic mass included in granite, head of Cottonwood Creek. 
Contains orthoclase, plagioclase, quartz, hornblende, biotite, apatite, 
and iron ore. A hornblende-mica-syenite. P. R. C. 554. 
K. Diorite, between Blackhawk and Robinson. Contains plagio- 
clase, orthoclase, quartz, biotite, diallage, hypersthene, iron ore, apa- 
tite, and zircon. P. R. C. 559. 
L. Basalt, Volcano Butte. Contains labradorite, augite, olivine, a 
little serpentine, occasional quartz grains, small patches of glass, iron 
ore, chiefly ilmenite, apatite, a trace of calcite, and a mineral which 
may be nephelite or analcite. P. R. C. 565. 
M. Augite -vogesite, dike on west side of upper Fourmile Creek. 
Contains augite, hornblende, iron ore, a little plagioclase, orthoclase, 
calcite, and some decomposition products. P. R. C. 563. 
N. Monchiquite-like dike rock, west side of upper Willow Creek. 
Contains augite, olivine, biotite, ilmenite, and a colorless base which 
appears to be partially zeolitized glass. Also a little serpentine, 
chlorite, and calcite. P. R. C. 564. 
H. 
I. 
J. 
K. 
L. 
M. 
N. 
Si0 2 
A1 2 3 
Fe 2 3 
FeO 
MgO 
CaO 
Na 2 
K 2 
H 2 
Ti0 2 
p 2 o 5 
Xa 
65.87 
16.82 
1.58 
1.23 
1.54 
2.65 
4.72 
3.15 
1.43 
.37 
trace 
61.21 
15.67 
4.06 
.62 
1.58 
2.18 
1.57 
2.75 
10.20 
.56 
61.87 
17.26 
2.35 
2.43 
1.82 
3.23 
5.18 
3.83 
1.07 
.87 
trace 
56.80 
18.30 
1.64 
5.58 
3.63 
5.31 
4.35 
3.28 
.53 
.46 
trace 
46.52 
10.48 
4.40 
7.79 
10.58 
9.49 
3.12 
1.55 
1.79 
2.98 
.83 
.73 
.11 
trace 
trace 
45. 15 
15.39 
2.76 
5.64 
6.38 
8.83 
2.67 
2.77 
2.85 
2.80 
.56 
42.46 
12.04 
3.19 
5.34 
12.40 
12.14 
1.21 
2.68 
4.03 
2.47 
.84 
MnO 
Li 2 
trace 
.10 
trace 
.03 
trace 
trace 
trace 
.14 
trace 
4.27 
.16 
trace 
.55 
C0 2 
Sp-gr 
99.36 
2.62 
100. 50 
99.94 
2.67 
99.88 
2.83 
100. 37 
2.99 
100. 21 
2.70 
99.51 
2.94 
a Unseparated rare earths or metallic acids, such as columbic, tantalic, etc. 
