IGNEOUS AND CRYSTALLINE ROCKS. 43 
I. Nepheline basalt, Black Mountain, Uvalde quadrangle. Uvaldose. Contains 
olivine, augite, nephelite, magnetite, and apatite. Sp. gr., 3.200, 21.5° PLR. «©, 
1066. 
J. The portion of I soluble in 1:40 dilute nitric acid. 
K. Augite from I. Violet in color, very pure. 
L. Nepheline-melilite basalt, from about 3 miles southwest of Uvalde. Casselose. 
Contains nephelite, melilite, olivine, augite, magnetite, and apatite. Sp. er., 3.150, 
20.5° P.R.C. 1064. 
M. The portion of L soluble in 1:40 dilute nitric acid. 
Rocks N to U collected by R. T. Hill in the trans-Pecos region. Descriptions sup- 
plied by Whitman Cross. Analyses by W. F. Hillebrand, record No. 1901. 
N. Rhyolite, summit of Chisos Mountain, Big Bend of the Rio Grande. Liparose 
near alaskose. Pink porphyry. Rich in alkali feldspars and quartz, with very little 
riebeckite and barkevikite (?). Sp. gr., 2.602, 15.5° 
O. Rhyolite, near Shafter, Shafter quadrangle. Liparose near alaskose. Pheno- 
crysts of sanidine and quartz. Groundmass of alkali fieldspars, quartz, riebeckite(?), 
and egirite. Spherulitic bands traverse the rock. Sp. gr., 2.617, 15.5° 
P. Rhyolite, north summit of Chisos Mountain. Liparose. Consists chiefly of 
alkali feldspars and quartz, with riebeckite and a little magnetite. Sp. gr., 2.611, 
15.5° 
Q. Rhyolite, west of Paisano Mountain, Alpine quadrangle. Liparose. Contains 
alkali feldspars, quartz, arfvedsonite, and egirite. Sp. gr., 2.635, 15.5°. 
