CLARKE.] 
IGNEOUS AND CRYSTALLINE ROCKS. 
101 
The four following rocks were collected by A. C. Spencer in 
Encampment quadrangle. Petrographic data supplied by Spencer. 
Analyses by E. T. Allen, record No. 2018. 
K. Norite, near head of Cow Creek, about three-fourths of a mile 
from Bridger Peak. Auvergnose. Contains chiefly hypersthene and 
labradorite, the latter slightly altered to sericite. Biotite and magnet- 
ite are present, with a few grains of diallage and a little hornblende. 
L. Diorite derived from norite, altered form of K. The pyroxene 
is completely changed to uralite, and the feldspar is largely decom- 
posed. 
M. Diorite derived from norite, 2 miles west of the Verdi mine. 
Contains uralite and labradorite, with a little biotite and magnetite. 
N. Diorite, probably derived from gabbro, near head of Big Sand- 
stone Creek. Contains much zoisite derived from the feldspars. 
Si0 2 .. 
Al-A- 
FeA 
FeO . . 
MgO. 
CaO.. 
Na,0 . 
H 2 at 105° . . . 
H 2 above 105° 
Ti0 2 
C0 2 
PA 
s 
CrA 
MnO 
BaO 
NiO, CoO. 
CuO 
K. 
52. 00 
11.59 
2.72 
7.18 
12.87 
10.49 
1.06 
.92 
.18 
.37 
.99 
none 
trace 
trace 
trace 
trace 
trace 
.04 
100. 41 
50. 08 
10.89 
2. 32 
7.99 
11.84 
9.73 
1.66 
.57 
.46 
2.61 
1.23 
.78 
.02 
trace 
trace 
trace 
.04 
none 
100. 1\ 
46. 39 
16. 17 
2. 65 
9. 30 
8. 58 
8. 90 
2.25 
.73 
.47 
2.59 
1.59 
none 
.06 
.01 
trace 
trace 
.02 
trace 
.02 
99. 73 
N. 
50.20 
15.54 
2. 14 
6.49 
7. 33 
11.96 
2.03 
.40 
.43 
2.52 
1.00 
none 
.09 
.03 
trace 
trace 
none 
100.16 
