138 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. [no. 228. 
G. Porphyrite, intrusive sheet, north of Shields River Basin. Aker- 
ose. Contains plagioclase, hornblende, and biotite, in a groundmass 
of plagioclase, a little orthoclase, augite, hornblende, and magnetite. 
H. Porphyrite, intrusive sheet, northern part of the mountains. 
Akerose. Contains brown hornblende, green augite, and plagioclase, 
in a groundmass of plagioclase, augite, and magnetite, with accessory 
apatite. 
I. Syenite, ridge north of Shields River Basin. Aherose. Con- 
tains hornblende, green augite, and anorthoclase, with accessory 
sphene, apatite, and magnetite. 
J. Diabase-porplryrite (?), dike south of Shields River Basin. 
I. 5. 3. If. Contains labradorite and decomposed augite in a ground- 
mass of plagioclase, epidote, and chlorite. 
K. Diorite-porphyrite, Big Timber Creek. Andose. Contains 
labradorite, augite, hornblende, biotite, orthoclase, quartz, magne- 
tite, and apatite. 
L. Quartz-diorite, main stock on Sweet Grass Creek. Andose. 
Contains hornblende, biotite, augite, labradorite, orthoclase, and 
quartz, with accessory apatite, magnetite, olivine, and hypersthene. 
Si0 2 .. 
A1A- 
Fe 2 3 
FeO.. 
MgO. 
CaO.. 
Na 2 . 
H. 2 OatllO°... 
H 2 above 110 c 
Ti0 2 
PA 
MnO 
SrO 
BaO 
Li 2 
CI 
co 2 
56. 75 
16.40 
4.78 
3.10 
3.22 
5. 34 
4.19 
3.36 
.40 
.82 
.86 
.52 
.17 
.10 
.33 
trace? 
100. 34 
II. 
54. 69 
16.53 
4.54 
2.83 
2.99 
5. 3,4 
5. 19 
3. 93 
.32 
1.05 
.91 
.73 
.07 
.06 
.37 
trace? 
trace 
.83 
100. 38 
58. 28 
17.89 
3.20 
1.73 
1.51 
3,. 69 
5. 89 
5. 34 
.17 
.98 
.64 
.26 
.06 
.05 
.36 
trace 
100. 05 
58.28 
19.37 
1. 35 
2.98 
1.30 
4.78 
4.40 
3. 75 
.44 
1.78 
.96 
.35 
.07 
.09 
.25 
trace? 
33 
100. 48 
54. 56 
17.58 
4.30 
4.98 
2.86 
6.00 
4.43 
2.70 
.02 
.38 
1.34 
.60 
.06 
.08 
.27 
trace 
100.16 
53. 48 
19.35 
2.37 
4.90 
3.67 
7.55 
4.07 
1.41 
.16 
.80 
1.07 
.62 
.06 
.11 
.19 
trace? 
.08 
99. 89 
