192 SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
nesian limestones, usually rather thin bedded, and some impure me- 
dium-grained quartzites of purple, gray, or white color. Hounded 
hills of gentle slope are developed in these slightly metamorphosed 
rocks. The Cambrian rocks are intensely metamorphosed near 
granite, and these facies have been described in the section on the 
Gold Mountain ridge (p. 183), along which they are more extensive! v 
developed. 
Xo fossils were found in these rocks, but from their lithologic simi- 
larity to the rocks in the vicinity of Lida and Cuprite they are with- 
out much doubt of Lower Cambrian age. 
Later tuffs. — Beneath the later rhyolite at several places is exposed 
a thin band of white tuffaceous sandstones, possibly to be correlated 
with the later tuffs of the Goldfield hills and Pahute Mesa. 
IGNEOUS ROCKS. 
Post -Jurassic granite. — Granite forms a considerable batholith on 
the west end of Slate Ridge and smaller intrusive masses and dikes 
occur in the Cambrian rocks. This rock is a coarse-grained biotite 
granite of pinkish tone. The pink or white feldspar and slightly 
smoky quartz individuals reach a maximum diameter of one-half 
inch, while the black biotite plates are smaller. The granite tends to 
weather into spherical masses. The surface, of these bowlders ap- 
pear- to undergo a kind of cementation, and on further weathering 
the hardened surface protrudes beyond the soft interior, forming 
mushroom-like forms. The granite breaks down into a soil of the 
constituent minerals and mechanical disintegration is so rapid that 
recent detrital deposits extend as broad basins well up into the hills. 
The granite is cut by parallel sheeting in certain localities and on 
weathering assumes the appearance of a sedimentary rock. Micro- 
scopic examination shows the texture to be allotriomorphic. The 
feldspar is orthoclase, considerably kaolinized and sericitized. Zir- 
con and magnetite are present as accessory minerals. 
Dikes of fine-grained biotite aplite, rather more siliceous than the 
granite, cut it, and these on weathering protrude from the granite 
mass. The granite is also cut by dikes and in turn grades into irregu- 
lar masses of coarse-grained pegmatite. Some quartz veins are evi- 
dently of pegmatitic origin, since they grade into less siliceous peg- 
matites. In some instances microscopic examination shows quartz 
individuals at the contact of granite and pegmatite to be common to 
both rocks. At the Bullfrog-George mine fluorite and molybdenite 
occur in a quartz vein which is without much doubt of pegmatitic 
origin. Molybdenite occurs sporadically in small tablets and irregu- 
lar areas in and between the quartz individuals. A bright-yellow 
mineral in minute crystals and tufted aggregates, apparently sec- 
ondary to molybdenite, was determined by Dr. Waldemar T. Schaller 
