132 SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
down, they broadly represent the main features. The latest rhyolite 
and later tuffs beneath the basalt in the northwestern portion of the 
mesa are not differentiated from the basalt, while the separation of 
the Siebert lake beds and the middle rhyolite near the Belted Range 
is only approximate. 
The list of the formations of Pahute Mesa, from the oldest to the 
youngest, is as follows: Mica schist, pre-granite monzonite, post- 
Jurassic granite, earliest rhyolite, biotite andesite, Siebert lake beds, 
middle rhyolite, latest rhyolite, later tuffs, and basalt. 
M ETAMORPHIC ROCKS. 
Mica schists. — At Trappmans Camp the granite contains fragments 
of mica schist, and an outcrop several hundred yards in diameter, 1 
mile east of Trappmans Camp, may extend eastward a considerable 
distance beneath the Tertiary lavas. These rocks are crenulated and 
foliated schists. One facies is a dark-brown schist apparently com- 
posed of tiny plates of biotite and muscovite well arranged in the 
plane of foliation. The microscope shows that the two micas are dis- 
tributed in rather distinct bands parallel to one another. Andalusite. 
sillimanite, and finely divided magnetite are present as accessories. 
Another facies is a silvery schisi composed of muscovite, with here 
and there an ellipsoidal aggregate of deep-green chlorite. Under thei 
microscope this proves to be a schist composed of the essential con- 
stituents, muscovite. chlorite, and quartz, and the accessory constitu-i 
ents, sillimanite, zircon, andalusite. and rutile. Nothing is know! 
concerning the age of these intensely metamorphosed rocks beyond the 
fact that they are much older than a granite of supposed post-Jurassi« 
age. They are perhaps of Cambrian age, since they somewhat resem- 
ble the more metamorphosed Cambrian schists near granite at Golc 
Mountain. 
SEDIMENTABY EOCKS. 
Paleozoic quartzite. — Prospectors report that quartzite occurs 01 
the north slope of Mount Helen, but the locality was not visited h} 
(lie writer. 
Siebert lajce beds. — The Siebert lake beds west of the Belted Rang< 
are similar to those described in the vicinity of Oak Spring. (See p 
122.) The beds are either horizontal or tilted up to angles of 30° 
Probably to be correlated with these are the white conglomerate 
sandstone 10 miles north of Tolicha Peak, and green tuffaceous sedi 
ments 7 miles southwest of Trappmans Camp. From the tuffaceou 
beds, which contain quartz, feldspar, and biotite crystals, Mr. B. E 
Stewart collected pieces of silicified wood which Dr. F. H. Knowltoi 
states belonged to a deciduous tree not older than the Tertiary. 
Later tuffs. — Beneath the basalt of Pahute Mesa east of Stonewal 
Mountain are tuffs and rhyolite flows which appear to be similar t ■ 
