KAWICH RANGE, IGNEOUS ROCKS. 
miles east of Rose Spring is intrusive in shaly sediments that are 
probably interbedded with the earlier rhyolite. This dacite is litho- 
logically identical with the daeite of the Goldfield hills and the two 
are probably contemporaneous and of middle Miocene age. 
Later rhyolite. — Forming the gently sloping flanks of the range 
west of Silverbow and capping some of the hills to the south of the 
same village is a brown, dense, and in many places glassy rhyolite 
characteristically poor in biotite and rich in quartz phenocryst 
Vesicles, elongated parallel to the flow banding, and vertical joints 
of cooling occur. In some places this rhyolite apparently lies upon 
the slightly eroded surface of the earlier rhyolite, and 5 miles south 
of Blakes Camp it appears, at a distance, to overlie the Siebert lake 
beds. The later rock has suffered much less erosion man the earlier 
rhyolite. The rock, so far as seen, was not altered by the mineraliz- 
ing waters which formed the ore deposits This rhyolite is younger 
than the supposed Siebert lake beds and is perhaps about contem- 
poraneous with the later rhyolite of the Belted Range. 
Later basalt and associated andesites. — Basalt caps the Kawich 
Range south of Quartzite Mountain. A number of basalt hills outcrop 
in the Reveille Valley, and on the east side of the range are a number of 
iow buttes partly of the same rock. The basalt of the south end of 
the range is black, dense, and more or less vesicular. The cone on the 
east flank of the mountains 10 miles east of north of Kawich is com- 
posed of a similar rock, in which a few small feldspar laths are the 
only conspicuous phenocrysts. Olivine basalts occur in the Reveille 
Valley. Basalt also forms a mesa 5 miles west of Silverbow. Andesite 
is associated with some of the basalt. The andesitic rocks of the 
Reveille Valley have a dense mottled reddish-gray or lilac-gray 
^roundmass. which is locally vesicular. The medium-sized pheno- 
crysts, which equal the base in mass, include glassy striated feldspar 
laths, many of which are twinned according to the Carlsbad law: 
fewer biotite plates, and hornblende or pyroxene columns. -Sphe- 
noidal weathering is rather characteristic. Flow breccias occur in 
)ands, and the rock appears to be closely related to the associated 
>asalts, each partially burying the small earlier rhyolite outcrop. A 
similar rock, although practically lacking biotite, forms a number of 
low, flat-topped hills G miles south of Kawich. Phenocrysts are 
ibundant in some facies and in others lacking. The rock occurs in 
lows which dip to the east. The hill 6 miles N. 30° E. of Kawich is 
capped by vesicular basalt beneath which are gray andesitic rocks 
vith glassy striated feldspar phenocrysts up to one-fourth inch in 
liameter. 
The basalt is similar to that of the Belted and Reveille ranges and 
s probably of late Pliocene or early Pleistocene age. The andesites 
re doubtless earlier manifestations of the same periods of volcanism. 
