162 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. [bull. 168. 
G. Syenite, between Tirbircio and Schurman gulches, La Plata 
Mountains. Contains much alkali feldspar, some oligoclase, augite, 
biotite, and hornblende, with a little titanite, magnetite, and apatite, 
Analysis by H. N. Stokes, record No. 1764. Sp. gr. 2.701, 25°. 
H. Monzonite, Babcock Peak, La Plata Mountains. Contains ortho- 
clase and plagioclase in about equal amounts, with augite and horn- 
blende, and a little quartz, titanite, magnetite, and apatite. Analysis 
by Stokes, record No. 1761. Sp. gr. 2.767, 26°. 
I. Porphyritic lamprophyre, allied to camptonite, Snowstorm Peak, 
La Plata Mountains. Contains numerous phenocrysts of green horn- 
blende, augite, and plagioclase, in a groundmass of plagioclase, ortho- 
clase, augite, magnetite, and apatite. Some secondary calcite. Anal- 
ysis by Hillebrand, record No. 1640. Sp. gr. 2.906, 21°. 
Si0 2 
A1 2 3 
Fe 2 3 
FeO 
MgO 
CaO 
Na 2 
K 2 
H 2 OatllO°... 
H 2 above 110 c 
Ti0 2 
PA 
VA-- 
NiO, CoO 
MnO 
SrO 
BaO 
Li 2 C) 
CO, 
so 8 ..: 
Cl 
FeS, 
55. 53 
16. 78 
4.06 
3. 35 
3. 00 
6.96 
4.31 
3. 57 
.09 
.55 
.95 
.47 
.02 
trace 
.16 
.11 
.13 
trace 
.09 
01 
100. 17 
60.44 
16. 65 
2.31 
3.09 
2.18 
4.22 
5.18 
2.71 
.36 
1.07 
.60 
.29 
.02 
none 
.13 
.11 
.12 
trace 
.48 
99. 96 
59.79 
17.25 
3.60 
1.59 
1.24 
3.77 
5.04 
5. 05 
.19 
.39 
.67 
.35 
.20 
.11 
.14 
trace 
.72 
.04 
trace 
100. 14 
H. 
57. 42 
18.48 
3.74 
2.10 
1.71 
6.84 
4.52 
3.71 
.08 
.28 
.86 
.36 
.09 
.08 
.15 
trace 
none 
none 
.03 
100. 45 
47.25 
15.14 
5.05 
4.95 
6.87 
9.98 
2.39 
2.60 
.40 
2.12 
1.22 
.25 
.05 
.02 
.17 
.05 
.08 
100. 46 
J. Porphyritic lampropLryre, allied to camptonite, Indian Trail 
Ridge, La Plata quadrangle. Contains phenocrysts of green horn- 
blende and colorless dioxide in a subordinate groundmass of plagioclase, 
orthoclase (?), augite, magnetite, and apatite. Much secondary cal- 
cite and some serpentine. Analysis by W. F. Hillebrand, record No. 
1610. Sp. gr. 2.912, 19.5°. 
