CLARKE.] 
IGNEOUS AND CRYSTALLINE ROCKS. 
141 
Rocks V, W, and X are described by Wolff in Bull. 150, pp. 197, 199, 
Y. Altered theralite, head of Shields River, west of Loco Mountain. 
Received from W. H. Weed. Analysis by H. N. Stokes, record No. 
1517. 
Z. Hornblende-picrite, Conical Peak. Aiwergnose. Data supplied 
by J. P. Iddings. Contains hornblende, plagioclase, hypersthene, 
augite, olivine, very little primary quartz, and probably some magnet- 
ite and apatite. Analysis by L. G. Eakins, record No. 1379. 
Si0 2 
A1A 
Fe 2 3 
FeO 
MgO 
CaO 
Na 2 
K 2 
H 2 OatllO°.... 
H 2 above 110° 
Ti0 2 
PA 
Cr 2 3 
MnO 
SrO 
BaO 
Li 2 
C0 2 
so 3 
CI L.. 
44. 65 
13.87 
6.06 
2.94 
5. 15 
9.57 
5.67 
4.49 
.96 
2.10 
.95 
1. 50 
.17 
.37 
.76 
trace 
.11 
.61 
trace 
92 
44.31 
17.20 
4.64 
3. 73 
6.57 
10. 40 
4.45 
3.64 
.77 
3.30 
undet. 
10 
47.67 
18.22 
3.65 
3.85 
6.35 
8.03 
4 93 
3.82 
.38 
2.97 
undet. 
28 
99.11 
100. 15 
48. 90 
14.70 
4.14 
3. 68 
3. 95 
8.26 
5.22 
.56 
.52 
2.44 
.95 
.70 
.03 
.13 
.31 
trace 
5.42 
.04 
100.04 
45. 71 
10. 80 
4.43 
9.35 
13. 75 
10.48 
1.58 
.85 
.97 
1.83 
.11 
.10 
.17 
trace 
100. 13 
5. LITTLE BELT MOUNTAINS. 
Rocks collected by W. H. Weed and L. V. Pirsson. Described in 
a paper on the Neihart and Barker mining districts in Pt. Ill of the 
20th Ann. Analyses by W. F. Ilillebrand, record No. 1170, and 
H. N. Stokes, record No. 1547. 
A. Quartz-porphyry, Yogo Peak, sheet at head of Belt and Run- 
ning Wolf creeks. Toscanose. Phenocrysts of orthoclase and quartz 
in a groundmass of quartz and alkali feldspar, with a little white mica 
and some kaolin. Chlorite, limonite, and calcite are also present, 
pseudomorphons after biotite and perhaps hornblende. Total amount 
of secondary minerals very small. Analysis by Ilillebrand. 
