ORDOVICIAN DEVONI AN . 
and Panamint ranges and in Bare Mountain, while transitional beds 
between it and the Eureka qnartzite occur in the Kav ich Range and 
a small area of what is probably the Pogonip limestone is situate 
in the Cactus Range. The limestone is dark gray, fine to medium 
grained, and dense. It is distinguished from the Cambrian lime- 
stones, already described, by a somewhat lighter color, ;i 
coarser and less crystalline texture, and rather more massive bed- 
ding. Near the center of the section, which ranges in thickness from 
2,000 to 4,000 feet, is about 100 feet of white or pinkish quartzite. 
The transitional rocks from the Pogonip to the overlying Eureka 
quartzite are an interbedded series of limestone, shale, and quartzite. 
The Eureka (Ordovician) quartzite described by Hague as over- 
lying conformably and without transitional beds tlu Pogonip lime- 
stone was recognized on stratigraphic grounds in the Amargosa 
and Kawich ranges, in the Bullfrog Hills, and on Bare Mountain, 
while in the Cactus Range and the hills between it and the Kawich 
Range quartzite areas isolated in Tertiary or Recent rocks are con- 
sidered its equivalent. The Eureka quartzite in southwestern Nevada 
is a typically white or pink, fine to medium grained, pure metamor- 
phosed quartzose sediment. Some beds, however, are conglomeratic 
quartzites, while others are argillaceous and grade into thin, inter- 
beaded sheets of dark-colored slaty shale. It varies from the quartz- 
ite of Hague chiefly in two characteristics — first, its greater thick- 
ness, reaching 1,200 to 1,500 feet in the Kawich Range, and, second, 
in being underlain by interbedded quartzites, shales, and limestones, 
transitional beds from the Pogonip limestone. 
Hague a gave to the uppermost division of the Ordovician and 
Silurian rocks at Eureka the name " Lone Mountain limestone.' 1 This 
formation lies unconformable upon the Eureka quartzite and is 
1,800 feet thick. It consists of black, gritty limestones at the base, 
which pass upward into light-gray, siliceous limestones. Its fos- 
sils include both Trenton and Niagara faunas. In the Amargosa 
and Kawich ranges and the Bullfrog Hills the Lone Mountain lime- 
stone is a gray, dense rock, of which about 400 feet is exposed. 
DEVONIAN. 
No Devonian formations were found in the course of the present 
work, and while such rocks may have been overlooked or may lie 
mrieel beneath Tertiary lavas it is tentatively believed that this 
Dortion of Nevada was a land mass during at least the greater part 
)f Devonian time. The alternative hypothesis is that the Devonian 
)eds were eroded away during post-Mississippian and pre-Penn 
ylvanian time, a period of important erosion in many portions of 
he West. 
a Hague, Arnold, Mon. U. S. Geol. Survey, vol. 20, 1892, pp. 57-59. 
