IGNEOUS AND CRYSTALLINE ROCKS. 
171 
3. COLFAX COUNTY. 
Descriptions, hitherto unpublished, supplied by Whitman Cross. 
Analyses by W. F. Hillebrand, record No. 1719. 
A. Phonolite, Pleasant Valley. Contains much nephelite, some 
segirite, alkali feldspar, a scanty dust of magnetite, and a few decom- 
posed grains of noselite or sodelite. Sp. gr. 2.619, 22°; 40.8 per 
cent soluble in dilute (1 : 10) nitric acid, of which soluble portion 43. 5 
per cent is silica. 
B. Pyroxene-andesite, Sierra Grande. Contains augite, less hyper- 
sthene, microliths of plagioclase, apatite, magnetite, and a smoky-brown 
glassy base. Sp. gr. 2.635, 21°. 
C. Plagioclase-basalt, end of San Rafael flow. Contains plagio- 
clase, augite, olivine, with much iddingsite, magnetite, and apatite. 
Sp. gr. 2.970, 21.5°. 
D. Nepheline-basanite, Ciruella. Contains augite, olivine, nephe- 
lite, plagioclase, magnetite, apatite, and a little biotite. Sp. gr. 3.122, 
22°. 0.55 per cent K 2 and 2.10 per cent Na 2 soluble in 1: 40 nitric 
acid. 
Si0 2 . 
Fe 2 3 . 
FeO.. 
MgO . 
CaO.. 
Na 2 0. 
H 2 at 110 c 
H 2 
Ti0 2 
P 2 5 
Zr0 2 .--. 
CrA-- 
V 2 3 . ... 
NiO, CoO 
MnO .... 
SrO 
BaO 
Li 2 
SO s 
s 
CI 
F 
56.24 
21:43 
2.01 
.55 
.15 
1.38 
10.53 
5.74 
.12 
.86 
.26 
.06 
.09 
none 
none 
.08 
.03 
.08 
trace 
.10 
.03 
.12 
trace 
B. 
60.16 
15.34 
3.07 
2.18 
3.41 
5.79 
3.88 
2.59 
.25 
1.79 
.84 
.46 
.01 
trace? 
trace 
.08 
.08 
.14 
trace 
.08 
trace 
midet. 
nndet. 
C. 
48. 35 
15.47 
4.80 
7.58 
8.15 
8.81 
3.09 
.95 
.28 
.73 
1.33 
.33 
none 
trace 
99.86 
100. 15 
.02 
.21 
.03 
.06 
trace 
.07 
trace 
undet. 
undet. 
100. 26 
42.35 
12.29 
3.89 
7.05 
13.09 
12.49 
2.74 
1.04 
.32 
1.50 
1.82 
.99 
none 
.10 
.04 
.03 
.21 
.09 
.10 
trace 
.05 
trace 
undet. 
undet. 
100. 19 
