KAWICH RANGE, IGNEOUS ROCKS. 
north end of the Reveille Range. If the correlation of the earlier 
rhyolite with the Tonopah rhyolite-dacite is correct, these beds 
probably the Siebert lake beds, of Miocene age. The last-mentioi 
exposure may, like the conglomerates of the Grapevine Range, be a 
shore deposit of this lake. 
IGNEOUS ROCKS. 
Post-Jurassic granite. — One mile west of Sumner Spring is an out- 
crop of gray granite porphyry with a dense groundmass containing 
many phenocrysts of feldspar three-fourths of an inch in length and 
rounded quartz individuals one-fourth inch in diameter. Under the 
microscope the groundmass shows as a fine mosaic of quartz and or- 
thoclase with a little plagioclase. With the phenocrysts of orthoclase 
and embayed quartz are some of plagioclase and very small tablets 
)f biotite altered to muscovite and a rutilelike substance. Apatite, 
zircon, and magnetite are accessory minerals. The relations of this 
mass to the earlier rhyolite are poorly exposed, but on lithologic 
grounds it is considered a post-Jurassic granite porphyry. 
Granite inclusions in rhyolite were observed at five widely sepa- 
rated localities. The varieties include fine- or medium-grained biotite 
granites, coarse-grained muscovite granite, pegmatitic quartz, and 
biotite granite with porphyrinic feldspar crystals similar to the gran- 
ite of Lone Mountain. Large bowlders of medium-grained biotite 
granite are so abundant in the Siebert lake beds 4 miles east of north 
)f Silverbow that a granite outcrop was probably near at hand when 
;he sandstone was deposited. 
Diorite porphyry. — Bowlders of diorite porphyry are associated 
vith those of granite in the area of Siebert lake beds just mentioned. 
The rock has a white, finely crystalline groundmass, in which are 
mbedded numerous white striated feldspar phenocrysts with a maxi- 
num length of one-fourth inch and smaller biotite phenocrysts. The 
ock is similar to the diorite porphyry of the Lone Mountain foothills 
md is probably a later manifestation of the post- Jurassic granite 
ntrusion. 
Monzonite porphyry. — Monzonite porphyry occupies an area 4 
niles long and 3 miles wide west of Kawich. It has a fine-grained 
lark or medium-gray groundmass, in which are embedded abundant 
menocrysts, many one-fourth inch, a few one-half inch long, of white 
>r greenish-white striated feldspar., brown biotite, and altered horn- 
blende. While both hornblende and biotite are usually present the 
Relative porportion of the two varies widely throughout the area. 
Oxidation of the iron of the rock produces pink and purple varieties. 
Ivhile kaolinization gives a white color. 
Microscopic examination shows the groundmass to be a medium- 
drained interlocking mosaic of orthoclase and plagioclase. Plagio- 
