BELTED RANGE. IGNEOUS HOCKS, 125 
acies, clearly bridges the interval between granite and granite 
mrphyry.. The granite cuts Pennsylvanian limestone and is doubtless 
ne of the post-Jurassic series. It rather strikingly resembles the 
|ranite outcropping 5 miles north of Ammonia Tanks. 
Several smaller masses of similar granite occur near the main 
?toek. The mass 11 miles east of south of Oak Spring lacks pheno- 
•rysts, and, since it is only 200 yards in diameter, is very similar in 
)ther respects to the contact facies of the main mass. It is medium 
pained or in a few places medium coarse grained. The granite is 
pore altered than that of the main mass, and the mica is usually 
nuscovite. apparently secondary to biotite. The granite grades into 
i coarse pegmatite, which in turn grades into pegmatitic quartz, 
Beh of which contains pyrite altered to limonite. The larger of the 
imonite cubes are one-half inch in diameter, and the pyrite was 
mdoubtedly an original constituent of the pegmatite. The pegmatite 
las some miarolitic cavities into which quartz and feldspar crystals 
I inch long project. A third mass of granite lies between the two 
ilready described, and two small outcrops isolated in the alluvial 
leposits appear to have been separated from the largest mass by 
rosion. 
\Andesite. — About 2! miles west of Wheelbarrow Peak is an ex- 
posure of andesite partially covered by the earlier rhyolite liows. 
The rock has a dense reddish-black groundmass, in which are em- 
)edded many medium-sized striated feldspar phenocrvsts, which are 
uther glassy and colorless or cloudy and white. Hand specimens 
suggest the presence of hornblende. v Under the microscope the 
groundmass appears as a glass containing many tiny laths of plagio- 
lase. The phenocrvsts are plagioclase (labradorite), brown horn- 
)lende, with a reaction rim of magnetite, which in some instances 
completely replaces the hornblende, and a little augite. The plagio- 
lase phenocrvsts, some of which are complex crystals, are somewhat 
ounded by magmatic corrosion and, as a rule, show beautiful zonal 
rowth. Inclusions of a greenish-gray andesite, rather similar, altho 
itli smaller feldspar phenocrvsts, occur in rhyolite near Cliff Spring, 
n the gravels of the. valley H miles west of Wheelbarrow Peak' are 
bowlders of a greenish-gray andesite. Phenocrysts of altered 
greenish-white feldspar are abundant, and associated with these are 
)iotite and either hornblende or pyroxene phenocrysts. The source 
>f this andesite is unknown) It strikingly resembles the post- 
hy otitic andesite of the Kawich Range and may perhaps be younger 
man the earlier rhyolite of the Belted Range. Certainly in this 
ange andesite older than the rhyolites occurs, while andesitic erup- 
ions may also have followed the rhyolitic effusion. 
Earlier rhyolite. — The earlier rhyolite is the predominant rock 
\t the northern part of Belted Range, and from its rather striking 
