168 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. 
[BULL. 168. 
3. MISCELLANEOUS ROCKS. 
A. Rhyolite, Thomas Range. Analysis made by L. G. Eakins in the 
Denver laboratory. Described by Cross in Proc. Colo. Sci. Soc., vol. 
2, p. 69. Contains phenocrysts of quartz and sanidine in a ground- 
mass mainly made up of quartz and alkali feldspar. 
B. Rhyolitic glass or pitchstone, edge of Gold Mountain mining dis- 
trict, 8 miles north of west from Marys vale. Identified by Whitman 
Cross, but not published. Sp. gr. 2.25 at 23.5°. Analysis by W. F. 
Hillebrand, record No. 1833. 
Si0 2 .. 
ALA- 
Fe 2 8 . 
FeO.. 
MgO . 
CaO.. 
Na 2 0. 
K 2 . . 
H 2 0.. 
Ti0 2 .. 
MnO. 
Li 2 0.. 
74.49 
14. 51 
.57 
.32 
trace 
1.03 
3.79 
4.64 
.64 
trace 
trace 
70.17 
11.83 
.93 
none 
.06 
.76 
3.85 
3.74 
8.72 
.17 
100. 23 
