124 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. 
[BULL. 168. 
Y. Altered theralite, head of Shields River, west of Loco Mountain. 
Received from W. H. Weed. Analysis by H. N. Stokes, record No. 
1547. 
Z. Hornblende-picrite, Conical Peak. Data supplied by J. P. 
Iddings. Contains hornblende, plagioclase, hypersthene, augite, oli- 
vine, very little primary quartz, and probably some magnetite and 
apatite. Analysis by L. G. Eakins, record No. 1379. 
Si0 2 . . 
A1A- 
FeO 
MgO 
CaO 
Na 2 
K 2 
H 2 OatllO°... 
H 2 above 110 c 
Ti0 2 
PA 
CrA 
MnO 
SrO 
BaO 
C0 2 
CI.. 
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 
99.92 
w. 
44.31 
17.20 
4.64 
3.73 
6.57 
10.40 
4.45 
3.64 
.77 
3.30 
undet. 
10 
99.11 
47.67 
18.22 
3.65 
3.85 
6.35 
8.03 
4.93 
3.82 
.38 
2.97 
undet. 
28 
100. 15 
Y. 
48.90 
14.70 
4.14 
3.68 
3.95 
8.26 
5.22 
.56 
.52 
2.44 
.95 
.79 
.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 
4. LITTLE BELT MOUNTAINS. 
Rocks collected by W. H. Weed and L. V. Pirsson, who furnish the 
petrographic data. To be described in a paper on the Neihart and 
Barker mining districts in Pt. Ill of the 20th Ann. Analyses by 
W. F. Hillebrand, record No. 1476, and H. N. Stokes, record No. 1547. 
A. Quartz-porphyry, Yogo Peak, sheet at head of Belt and Running 
Wolf creeks. 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, pseudomorphous after 
biotite and perhaps hornblende. Total amount of secondary minerals 
very small. Analysis by Hillebrand. 
