PANAMINT RANGE, IGNEOUS ROCKS. 
the area surveyed. The rock is light greenish gray in color and has 
prominent white feldspar phenocrysts from one-eighth to one-fourth 
inch in length, which are in parallel alignment t trough flow. The 
rock has suffered considerable epidotization. Under microscope ii 
proves to be a much-altered diorite porphyry with a groundmass of 
plagioclase laths and a little orthoclase. Aggregates of epidote, 
zoisite, and chlorite and a smaller amount of calcite are evidently 
pseudomorphs of plagioclase and hornblende phenocrysts. Tli 
rock is evidently the pre-Tertiary diorite porphyry. 
Basalt. — Six small masses of basalt occur in the southern portion 
of the Panamint Range, and the same rock caps a considerable area 
at the north end of the range, where it occurs in several flows, each 
500 or more feet thick, interbedded with the older alluvium. The 
small basalt mass If miles south of west of the head of Cottonwood 
Creek is a north-south dike 250 feet wide. The basalt on the borders 
of this dike is vesicular and includes numerous quartz-monzonite 
fragments. The outcrop on the Cottonwood Canyon trail three- 
fourths of a mile above its entrance into the mountains may also be 
a dike cutting the Carboniferous limestone. The other masses are 
erosional remnants of a single flow or of contemporaneous flows. 
The prebasaltic mature Panamint Range in consequence must have 
been cut deeply by canyons on its borders, while the old surface to the 
south and southwest of the area mapped was but little dissected when 
the basalt was extruded. The flow on the east side of Emigrant 
Wash forms a black bluff 200 feet high, which is a prominent land- 
mark for many miles. The flow 4 miles east of the dike is 400 feet 
thick and forms a mesa. 
The basalt has a dense dark-gray groundmass mottled by light- 
gray areas. It is more or less vesicular, the largest cavities being - 
inches long and usually elongated parallel to the direction of flow. 
Calcite, quartz, and zeolites fill the vesicles more or less completely. 
The phenocrysts, which are usually subordinate to the groundmass, 
include blebs of olivine, more or less altered, and striated feldspars 
up to one-fourth inch in length, some of them showing zonal growth. 
Greenish-black augite is less commonly present. Under the micro- 
scope the basalt shows a dark, greasy groundmass, in which are 
microlitic laths of basic plagioclase and pyroxene col minis. The 
phenocrysts include laths of basic plagioclase; rounded grain- of 
olivine, usually fresh, although in places altered to iron-stained ser- 
pentine, and columns of grayish pyroxene, much of it twinned. The 
basalt is usually well jointed and weathers into spheroidal masses. 
The basalt east of Emigrant Wash and the flow on the Cottonwood 
Canyon trail lie unconformably below the older alluvium. 
Bull. 308—07 m 14 
