IGNEOUS AND CRYSTALLINE ROCKS. 111 
7. ELK MOUNTAINS. 
Analyses made by L. G. Eakins in the Denver laboratory. Petrographic data 
supplied by Whitman Cross. 
A. Rhyolite, East Mountain, Crested Butte district. Alsbachose. Phenocrysts of 
orthoclase, oligoclase, quartz, and biotite, in a microspherulitic and cryptocrystalline 
groundmass. P.R. C. 514. 
B. Rhyolite, Round Mountain, Crested Butte district. Toscanose. Small pheno- 
crysts of quartz. sanidine, biotite, and oligoclase, in a groundmass of quartz and 
orthoclase. P. R. C. 513. 
C. Diorite, Brush Creek, Gunnison County. Tonalose. Contains several varieties 
of plagioclase, with orthoclase, quartz, hornblende, biotite, augite, sphene, apatite, 
and magnetite. P. R. C. 93. 
100.07 | 100.20 100. 33 
Biyori ctcr Renata Sea a terete ot ni ecracte ter chetceth oa 2.38, 17° | 2.59, 18° aber 
8. WEST ELK MOUNTAINS. 
Rocks described by Cross in 14th Ann., p. 165. 
A. Hornblende-mica porphyrite, Cliff Creek. Adamellose. Contains plagioclase, 
hornblende, and biotite, in a groundmass of quartz, feldspar, and mica. Analysis 
by W. F. Hillebrand, record No. 1429. 
B. Porphyrite, Storm Ridge. Yellowstonose. Contains plagioclase, biotite, hyper- 
sthene, hornblende, and augite, in a groundmass of quartz and orthoclase. Analysis 
by L. G. Eakins, record No. 1238. P.R. C. 517. 
C. Porphyrite-diorite, Mount Marcellina. Yellowstonose. Contains plagioclase, 
hornblende, and a little biotite, in a groundmass of quartz.and orthoclase. Analysis 
by T. M. Chatard, record No. 1238. P. R. C. 516. 
D. Quartz porphyrite, Mount Carbon. Amiatose. Contains plagioclase, ortho- 
clase, biotite, hornblende, augite, and quartz. Analysis by Chatard, record No. 1238. 
P.R. C. 518. 
E. Quartz porphyrite, Crested Butte. Lassenose. Contains plagioclase, orthoclase, 
hornblende, biotite, quartz, and a little augite. Analysis made by Eakins in the 
Denver laboratory. P. R. C. 515. a 
