152 
ANALYSES OF ROCKS, U. S. GEOLOGICAL SURVEY. 
[BULL. 168. 
The following analyses, all by L. G. Eakins, do not appear in the 
published memoir just cited. A and B were made in the Denver lab- 
oratory. The petrographic details have been supplied by Whitman 
Cross. 
A. Spherulite in rhyolite, ridge west of Mount Tyndall. Mainly 
composed of quartz and feldspar needles, with some f erritic coloring 
due to decomposition of trichites. 
B. Rhyolitic residual glass, same locality as A. 
C. Interspheruiitic mass, Rosita. Record No. 1285. 
D. Spherulite, Rosita. Record No. 1286. 
E. F, G. Spherulites, Silver Cliff. Record Nos. 1285, 1286. 
These spherulites, C, D, E, F, and G, are made up of orthoclase 
needles, with free silica in libers or grains, or rarely as tridymite. 
The "soluble silica" is that which is dissolved by sodium carbonate 
solution. 
Si0 2 . . 
A1 2 3 . 
Fe 2 3 
FeO.. 
MgO. 
CaO- 
K 2 0. 
H 2 0. 
PA 
MnO 
Soluble Si0 2 
71.27 
16.02 
1.41 
.17 
trace 
.35 
5.76 
4.08 
1.14 
trace 
trace 
100. 20 
B. 
85.50 
7.42 
1.23 
.34 
.82 
.37 
.74 
2.64 
1.22 
none 
100. 36 
C. 
74.47 
13.87 
trace 
.51 
2.10 
7.46 
1.88 
100. 29 
12.72 
80.61 
10.94 
.09 
.26 
2.90 
3.02 
2.20 
100. 02 
11.12 
E. 
83.91 
9.54 
trace 
.19 
.62 
5.06 
.69 
100. 01 
1.06 
79.21 
12.24 
.11 
.43 
2.58 
5.26 
100. 49 
1.27 
G. 
78.77 
12.46 
.09 
.34 
2.12 
5.84 
.70 
100. 32 
1.25 
