194 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. 
[no. 228. 
2. MOUNT TAYLOR REGION. 
Rocks received from J. S. Diller. Analyses by T. M. Chatard, 
record Nos. 219, 227, 228, 235, 271, 268, and 269. Not hitherto pub- 
lished. Petrographic details furnished by Diller. 
A. Lava, canyon on east side of San Mateo Mountain. Kallerudose. 
B. Phonolitic andesite, can}^on on east side of San Mateo Mountain. 
JSfordmarlcose. Contains feldspar and corroded augite, with some- 
times olivine, in a groundmass of feldspar and a green ferromagnesian 
silicate. 
C. Mica-andesite, can}^on on east side of San Mateo Mountain. 
Lassenose. Shows prominent plagioclase, with augite and biotite. 
D. Mica-andesite, 6 miles northeast of Grant's. Principally plagio- 
clase and biotite, with less epidote, quartz, sphene, and carbonates. 
E. Basalt, 6 miles northeast of Grant's. Auvergnose. Contains 
chiefly plagioclase, augite, and olivine, with much magnetite. 
F. Augite from E. 
G. Feldspar from E. Analysis on three-fourths gramme of material. 
Si0 2 
AlA---- 
FeA ... 
FeO 
MgO .... 
CaO 
Na,0 .... 
K 2 
H 2 
TiO, . . . . 
PA.... 
CrA---- 
MnO . . . . 
(CoNi)O 
BaO 
CO., 
A. 
68.40 
17.99 
2.66 
1.63 
.49 
.67 
4.54 
3.54 
.52 
21 
100. 65 
B. 
65.51 
16. 89 
1.41 
2.52 
.39 
1.19 
6.42 
5.02 
.16 
.92 
.07 
31 
c. 
D. 
65. 78 
49. 80 
17.32 
15.33 
3.68 
.46 
7.44 
.47 
6.61 
1.66 
7.19 
5.23 
2.71 
4.64 
4. 36 
.14 
1.38 
.27 
2.67 
.13 
.73 
.32 
.30 
100. 81 
100. 10 
2.56 
101. 08 
47.54 
16. 73 
6.69 
6.67 
6.38 
8.74 
2.81 
1.10 
.36 
2.76 
.51 
.19 
. 03 
(?) 
100. 51 
47.06 
7.77 
1.30 
8.15 
13. 52 
19.33 
.33 
.11 
.20 
1.82 
.06 
trace 
.20 
traces 
99. 85 
G. 
52.54 
31.26 
.28 
12.34 
3.55 
.42 
.26 
undet. 
trace? 
100. 65 
3. COLFAX COUNTY. 
Descriptions, hitherto unpublished, supplied by Whitman Cross. 
Analyses by W. F. Hillebrand, record No. 1719. 
A. Phonolite, Pleasant Valley. MiasJcose. Contains much nephe- 
lite, some aegirite, alkali feldspar, a scanty dust of magnetite, and a 
