CLARKE.J 
IGNEOUS AND CRYSTALLINE ROCKS. 
159 
7. ELK MOUNTAINS. 
Analyses made by L. G. Eakins in the Denver laboratory, and hith- 
erto unpublished. Petrographic data supplied by Whitman Cross. 
A. Rhyolite, East Mountain, Crested Butte district. Phenocrysts 
of orthoclase, oligoclase, quartz, and biotite, in a microspherulitic and 
|ryptocrystalline groundmass. P. R. C. 514. 
B. Rhyolite, Round Mountain, Crested Butte district. Small phe- 
nocrysts of quartz, sanidine, biotite, and oligoclase, in a groundmass 
of quartz and orthoclase. P. R. C. 513. 
C. Diorite, Brush Creek, Gunnison County. Contains several varie- 
ties of plagioclase, with orthoclase, quartz, hornblende, biotite, augite, 
bhene, apatite, and magnetite. P. R. C. 93. 
Si0 2 . 
AU), 
Fe 2 3 
FeO. 
MgO 
CaO. 
Na 2 
MnO 
Sp. gi 
74.84 
14.05 
.17 
.31 
trace 
1.57 
3.66 
3.14 
2.33 
100. 07 
2. 38, 17° 
B. 
71.56 
14.91 
1.47 
1.04 
.08 
1.98 
3.78 
4.94 
.44 
trace 
100. 20 
2. 59, 18° 
c. 
62.71 
17.06 
3.79 
2.74 
1.78 
5.51 
3.54 
2.96 
.24 
none 
trace 
100. 33 
2. 791, 30 c 
