174 
ANALYSES OF KOCKS, U. S. GEOLOGICAL SURVEY. [no. 228. 
L). Gray porphyry, Johnson Gulch, near Leadville. Yellowstonose. 
Slightly altered. Contains orthoclase, plagioelase, biotite, and quartz, 
with decomposition products probably derived from original horn- 
blende. Sp. gr., 2.736, 16°. Analysis by Hillebrand. 
E. Pink orthoclase crystals from D. Analysis by Hillebrand. 
F. Hornblendic porphyrite, lower Buckskin Gulch. Andose. Con- 
tains plagioelase, orthoclase, quartz, hornblende, biotite, magnetite, 
apatite, and zircon, with a little secondary calcite and chlorite. Sp. 
gr., 2.768, 16°. Analysis by Hillebrand. P. R. C. 89 and 506. 
G. Biotite-porphyrite, dike in gneiss in the North Mosquito amphi- 
theater. Tonalose. Composition like F, but with no hornblende, 
much biotite, and some pyrite. Sp. gr., 2.740, 16°. Analysis by 
Hillebrand. P. R. C. 507. 
Si0 2 .. 
A1A- 
FeA 
FeO.. 
MgO . 
CaO.. 
Na 2 0. 
K 2 0.. 
H 2 0.. 
Ti0 2 . 
PA - 
MnO. 
SrO . . 
C0 2 .. 
CI.... 
FeS 2 . 
68.10 
14.97 
2.78 
1.10 
1.10 
3.04 
3.46 
2.93 
1.28 
.07 
.16 
.09 
.08 
.92 
.03 
100. 11 
62.22 
20.33 
2.95 
3.45 
8.31 
1.90 
99.16 
F. 
56.62 
16.74 
4.94 
3.27 
4.08 
7.39 
3.50 
1.97 
.92 
trace 
.15 
trace 
1.15 
100. 73 
G. 
64.81 
15.73 
1.68 
2.91 
2.82 
4.22 
3.98 
1.43 
.62 
.08 
.23 
.08 
trace 
1.08 
.04 
.90 
100. 61 
