CLARK K.J 
IGNEOUS AND CRYSTALLINE ROCKS. 
155 
D. Gray porphyry, Johnson Gulch, near Leadville. Slightly al- 
altered. Contains orthoclase, plagioclase, biotite, and quartz, with 
decomposition products probably derived from original hornblende. 
Sp. or. 2.736, 10°. Analysis by Hillebrand. 
E. Pink orthoclase crystals from D. Analysis by Hillebrand. 
F. Hornblendic porphyrite, lower Buckskin Gulch. Contains pla- 
gioclase, 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. 506. 
G. Biotite-porphyrite, dike in gneiss in the North Mosquito amphi- 
theater. Composition like F, but with no horblende, much biotite, 
and some pyrite. Sp. gr. 2.740, 16°. Analysis by Hillebrand. P. 
K. C. 507. 
Si0 2 .. 
A1 2 3 - 
Fe 2 3 . 
FeO.. 
MgO. 
CaO.. 
Na 2 0. 
K 2 . . 
H 2 0.. 
Ti0 2 _. 
PA- 
MnO. 
SrO.. 
C0 2 .. 
01.... 
FeS,.. 
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. 1 1 
62.22 
20.33 
2.95 
3.45 
8.31 
1.90 
99. 16 
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 
