122 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. 
[BULL. 168. 
M. Diorite, head of Rock Creek. Contains biotite, labradorite, and 
augite, in a groundmass of plagioclase, orthoclase, and quartz, with 
accessory magnetite, apatite, and hornblende. 
N. Diorite, main stock, Big Timber Creek. Contains biotite, augite, 
labradorite, quartz, orthoclase, apatite, and magnetite. 
O. Olivine-gabbro, Big Timber Creek. Contains labradorite (?), 
brown hornblende, augite, olivine, and magnetite. 
P. Rock from Musselshell River, north of Crazy Mountains. Re- 
ceived from J. S. Diller, but undescribed. Regarded by W. H. Weed 
as monchiquite. Analysis by L. G. Eakins, record No. 1021. 
Q. Hornstone, metamorphosed shale, contact zone, Sweet Grass 
Creek. An aggregate of augite, quartz, triclinic feldspar, and biotite. 
M. 
N. 
0. 
P. 
Q. 
Si0 2 
57.97 
15. 65 
.73 
2.80 
4.96 
10.93 
3.03 
3.16 
.22 
.38 
.60 
.15 
50. 73 
19.99 
3.20 
4.66 
3.48 
8.55 
4.03 
1.89 
.11 
.66 
1.59 
.81 
40.42 
9.98 
9.83 
10.67 
11.56 
10.78 
1.26 
.60 
.45 
1.17 
2.51 
.63 
.02 
.25 
.02 
.05 
trace 
44.66 
12.12 
5.81 
3.20 
8.77 
8.14 
4.47 
2.75 
1 4.33 
1.02 
2.02 
57.31 
14.24 
1.00 
3.24 
4.60 
11. 31 
2.64 
4.55 
.25 
.24 
.52 
.18 
A1 2 3 
Fe 2 3 
FeO 
MgO 
CaO 
Na 2 
K 2 
H 2 at 110° 
H 2 above 110° 
Ti0 2 
P 2 5 
(CoNi) 
MnO 
trace 
.02 
.09 
trace 
.05 
.11 
.27 
trace 
.21 
.08 
trace? 
.19 
trace? 
.17 
SrO 
BaO 
Li 2 
C0 2 
2.19 
CI 
F 
trace 
trace 
100.69 
100. 13 
100. 20 
99.69 
100. 52 
