66 SOUTHWESTERN NEVADA AND EASTERN CALIFORNIA. 
MOUNT JACKSON AND THE HILLS TO THE NORTHEAST. 
TOPOGRAPHY AND GEOGRAPHY. 
Mount Jackson is a prominent butte which rises 800 feet above its 
alluvial base. Northeastward from it extends a ridge on which are 
superimposed buttes of the Mount Jackson type, capped by resist- 
ant lava flows. At its north end this ridge is divided by a valley into 
two parts. These lull- arc separated from the (Joldfield hills to the 
north by basalt lava Hows. For convenience the mesa-capped hill east 
of Cuprite 1 and the isolated hills 10 miles east of north of Mount Jack- 
son will be described here. 
Water is unknown in these hills, and with the exception of scat- 
tered groves of the tree yucca they are hare. Grass is fairly abundant 
on the upper portions of the encircling alluvial slopes. 
GENERAL GEOLOGY. 
The formations exposed in these hills, named from the base up- 
ward, are Cambrian sedimentary rocks, diorite porphyry, Siebert lake 
beds, rhyolite, and basalt. 
SI m \i I \T \i;y ROCKS. 
Cambrian. — An area in the southern ridge and another at the north 
end of the northern ridge are occupied by Cambrian sedimentary 
rocks, and the same rock- also in part form the isolated hills in the 
valley traversed by the Goldfield-Lida road. 
A compact fine-grained black or dark-gray limestone, locally silici- 
fied to a black jasperoid of conchoidal fracture, is the dominant mem- 
ber of the Cambrian series. Both rocks are intricately cut by white 
calcite veinlets. Layers of thin-bedded green slaty shale, in place! 
schistose, are interbedded with the limestone, as are smaller amounts 
of white medium-grained quartzite. A total thickness of 3,000 to 
3,500 feet of Cambrian rock is exposed. These sediments form gentle 
hills elongated in the direction of strike, the shales being character- 
ized by few. the limestone and quartzite by many exposures. 
Mr. E. <). Ulrich determined the following fossils collected by the 
writer near the (ioldfield-Mid way-Bullfrog mining camp, 2 miles south 
of west of Cuprite: Olenellus, near O. gilberti; Hyolithes, closely 
related to or identical with //. americanus; undetermined orthoid 
shell. 
He states: " So far as this imperfect material will permit of deter- 
mining age, it points to a Lower Cambrian horizon." Girranella-Yflsa 
forms similar to those from the Silver Peak Range were also found 
in these Cambrian rocks. The Lower Cambrian age of portions of the 
series is thus demonstrated, although other portions may be somewhat 
younger. The rocks are correlated with those of the north spur of the 
Silver Peak Range and of the Lone Mountain foothills. 
