156 SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
is a glassy quaytz in which are many biotite flakes one-eighth inch in 
diameter. A few black tourmaline rods up to one-fourth inch long 
occur in a quartz-rich muscovite pegmatite. While some of the 
tourmaline occurs in nests of clustered rods, some also forms along 
minute cracks and appears to be of pneumatolitic origin. Pegma- 
titic quartz vein- with small quantities of feldspar and muscovite are 
very common, and it is probable that many of the older quartz veins 
were deposited by waters from the granite magma. The pegmatite 
dikes cut Paleozoic rocks and arc included in the Tertiary volcanic 
rocks, and arc probably post-Jurassic in age. They closely resemble 
the pegmatite- west of Bullfrog. 
D.iorite porphyry. — Bowlders of the biotite-monzonite porphyry 
or diorite porphyry occur on an alluvial fan a( the northwest edge of 
Bare Mountain. Dikes of this rock, possibly of pre-Tertiary age, 
probably cut the Paleozoic rocks. 
Tertiary rhyolite and basalt. — Flows of rhyolite and basalt form 
the north end of the Bare Mountain hills. These are similar litho- 
logieally to the rhyolite and later basalt of the Bullfrog Hills. (See 
pp. 180-181.) 
STRUCTURE. 
The Paleozoic rocks of P>are Mountain form a faulted monocline, 
the beds of which strike from north of west to northwest and dip 
from 15° to 80 c NK. Superimposed upon the monocline are minor 
cross fold-. The schist and in a less degree the limestone are closely 
crenulated and small isoclinals and overturned folds are common. 
The folding was so intense that schist hand- between limestone and 
quartzite are severed on the limbs of the folds and greatly thickened 
at the crests and troughs. At least two profound normal faults of 
over 1,000 feet displacement cut the Paleozoic rocks, and other faults 
of almost equal magnitude exist. Small faults, both normal and 
reverse, are common. Joints traverse all the formations, but are 
particularly developed in the quartzite, which in consequence breaks 
down into squared block'-. 
Prior to the extrusion of the Tertiary rhyolite the range stood out 
boldly and was probably a- high or almost as high as at present. The 
differential movement which has occurred at the contact of the Pale- 
ozoic and Tertiary rocks is unimportant. 
ECONOMIC GEOLOGY. 
Quartz veins are common in the north end of the range, and min- 
eral locations were made on some of them early in 1905. Older veins, 
which were folded with the Paleozoic rocks, are cut and faulted by 
a younger set. All the quartz veins are characterized by rather 
abrupt variations in width. 
The Decillion claim is located in the northwestern portion of the 
