74 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. 
[no. 228. 
Rocks N to U collected by R. T. Hill in the trans-Pecos region. 
Descriptions supplied by Whitman Cross. Analyses, hitherto unpub- 
lished, by W. F. Hillebrand, record No. 1901. 
N. Rhyolite, summit of Chisos Mountain, Big Bend of the Rio 
Grande. Liparose near alaskose. Pink porphyry. Rich in alkali 
feldspars and quartz, with very little riebeckite and barkevikite (?). 
Sp. gr., 2.602, 15.5°. 
O. Rhyolite, near Shafter, Shafter quadrangle. Liparose near 
alaskose. Phenocrysts of sanidine and quartz. Groundmass of 
alkali-feldspars, quartz, riebeckite (?), and regirite. Spherulitic bands 
traverse the rock. Sp. gr., 2.017, 15.5°. 
P. Rhyolite, north summit of Chisos Mountain. Liparose. Con- 
sists chiefly of alkali-feldspars and quartz, with riebeckite and a little 
magnetite. Sp. gr., 2.611, 15. 5 C . 
Q. Rhyolite, west^of Paisano Mountain, Alpine quadrangle. Lip- 
arose. Contains alkali-feldspars, quartz, arfvedsonite, and segirite. 
Sp. gr., 2.635, 15.5 . 
x. 
Si0 2 76. 30 
ALA ! 11-53 
1.83 
76 
.03 
16 
4.01 
4.70 
19 
34 
I .16 
11 
trace 
none 
FeA 
FeO 
MgO 
CaO 
Na 2 
K,0 
H 2 at 105° . . . 
H 2 above 105 c 
Ti0 2 
Zr0 2 
C0 2 
PA 
SO, 
s 
MnO 
BaO 
SrO 
Li 2 
Rare earths . . . 
trace 
trace 
none 
none 
trace 
.02 
0. 
75.12 
10.94 
2.88 
.86 
.07 
.20 
4.46 
4.54 
.18 
.19 
.20 
.13 
.04 
none 
none 
.05 
.08 
none 
none 
trace 
.04 
100.14 99.98 
74.85 
12.83 
1.40 
.37 
.04 
.48 
4.24 
5.12 
.24 
.30 
.15 
.09 
trace? 
trace 
100.18 
72.86 
11.74 
2.71 
1.66 
.06 
.24 
4.63 
4.92 
.51 
.40 
.20 
.28 
trace 
trace 
trace 
trace 
trace 
.07 
none 
none 
none 
none 
trace 
trace 
.07 
.05 
100.33 
CI and F not looked for. 
