IGNEOUS AND CRYSTALLINE ROCKS. 117 
K. Tinguaite (?), Two Buttes. Laurdalose. Collected by G. K. Gilbert; petro- 
graphic data supplied by Whitman Cross. Consists chiefly of pale-green augite, horn- 
blende, apatite, magnetite, and occasional crystals of alkali feldspar, in an obscure, 
largely isotropic groundmass. Sp. gr., 2.79, 25° P. R. C. 1393. 
L. Pyroxene from I’. Sp. gr., 3.43, 28°. 
M. Portion of F soluble in 1:40 nitric acid. 
N. Syenitic lamprophyre (?), Two Buttes. Prowersose. Collected by Gilbert; 
described by Cross in Jour. Geol., vol. 14, p. 165. Chief constituents, diopside, 
alkali feldspar, considerable biotite, magnetite, and olivine. The ferromagnesian 
minerals predominate. Sp. gr., 2.88, 29°. P. R. C. 1394. 
QO. Pyroxene from I. Sp. gr., 3.45, 25°. 
P. Portion of I soluble in 1:40 nitric acid. 
Analyses F to K by W. F. Hillebrand, record No. 1604. 
trace | trageE| carcas satiate oon 
100.68 | 100.21 | 33. 06 | 100. 42 | 100.27) 5.81 
| 
Rocks Q to V collected by Whitman Cross, who supplies the petrographic data. 
Hitherto unpublished, except when otherwise stated. 
Q. Rhyolitic vitrophyre, near Del Norte, Rio Grande County. Toscanose. Re- 
ported by Cross as containing phenocrysts of oligoclase, quartz, biotite, and augite in 
a dark, fresh, glassy groundmass, the latter being predominant. Analysis made by 
Eakins in the Denver laboratory. Sp. gr., 2.423, 14°. P.R. C. 164. 
R. Rhyolite, Summit district, Rio Grande County. Toscanose. Large pheno- 
crysts of sanidine, with smaller ones of oligoclase and biotite, in a groundmass of 
orthoclase, quartz, oligoclase, biotite, and magnetite. Analysis by Eakins, made in 
the Denver laboratory. Sp. gr., 2.489, 14° ; 
8. Quartz monzonite, Sultan Mountain, San Juan County. <Amiatose. Contains 
plagioclase, orthoclase, quartz, augite, biotite, magnetite, and apatite. Some chlorite 
and epidote as alteration products. Analysis by L. G. Eakins in the Denver labora- 
tory. Sp. gr., 2.751, 14°. Described by Cross in 21st Ann., pt. 2. P.R. C, 204. 
T. Pyroxene-hormblende andesite, Falls Creek, Lake City quadrangle. Consists 
chiefly of plagioclase, augite, hypersthene, and hornblende, with little magnetite 
and apatite, and an abundant glass base. Analysis by G. Steiger, record No. 2244. 
U. Decomposed andesite, Slumgullion mud flow, Lake City quadrangle. Analysis 
by W. T. Schaller, record No. 2368. 
V. Trachyte, Grayrock Peak, Engineer Mountain quadrangle. Analysis by 
Steiger, record No. 2374. 
15619—Bull, 419—10——9 
