160 
ANALYSES OF ROCKS U. S. GEOLOGICAL SURVEY. 
[BULL. 168. 
8. WEST ELK MOUNTAINS. 
Rocks described by Cross in 14th Ann., p. 165. 
A. Hornblende-mica-porphyrite, Cliff Creek. Contains plagioclase, 
hornblende, and biotite, in agroundmass of quartz, feldspar, and mica. 
Analysis by W. F. Hillebrand, record No. 1429. 
B. Porphyrite, Storm Ridge. Contains plagioclase, biotite, hyper- 
sthene, hornblende, and augite, in a groundmass of quartz and ortho- 
clase. Analysis by L. G. Eakins, record No. 1238. P. R, C. 517. 
C. Porphyrite - diorite, Mount Marcellina. ■ Contains plagioclase, 
hornblende, and a little biotite, in a groundmass of quartz and ortho- 
clase. Analysis by T. M. Chatard,* record No. 1238. P. R. C. 516. 
D. Quartz-porphyrite, Mount Carbon. Contains plagioclase, ortho- 
clase, biotite, hornblende, augite, and quartz. Analysis by Chatard, 
record No. 1238. P. R. C. 518. 
E. Quartz-porphyrite, Crested Butte. Contains plagioclase, ortho- 
clase, hornblende, biotite, quartz, and a little augite. Analysis made 
by Eakins in the Denver laboratory. P. R. C. 515. 
A. 
B. 
c. 
D. 
E. 
Si0 2 
63.05 
15.58 
2.92 
2.11 
' 1.70 
4.15 
3.77 
3.66 
.55 
1.38 
.60 
.27 
.12 
.07 
.13 
trace 
61.42 
17.69 
4.24 
1.74 
1.81 
5.29 
3.14 
3.19 
| .97 
.37 
.14 
.19 
62.85 
16.21 
3.08 
1.46 
1.47 
4.72 
3.49 
3.10 
.29 
2.03 
.41 
.48 
.15 
65.36 
15.48 
3.09 
1.21 
1.53 
4.14 
3.58 
3.41 
.82 
.70 
.52 
.25 
.19 
65.71 
18.30 
1.19 
1.53 
.98 
2.17 
5.00 
3.95 
} 1.39 
undet. 
A1 2 3 
Fe 9 0, 
FeO 
MgO 
CaO 
Na 2 
K 2 
H 2 Oatl00° 
H 2 above 100°..... 
Ti0 2 
P,0. 
MnO 
.02 
SrO 
BaO 
.09 
.11 
.08 
Li 2 
100. 06 
100. 28 
99.85 
100. 36 
100. 24 
