264 The American Geologist. May, 1902. 
peints. Although a part of the complex, this white granite is 
regarded as later than the overlying dolomyte for it appears to 
be intrusive in it. Coarse white pegmatyte dikes cut all the 
rocks of the complex. They are probably genetically related 
to the white-granite. 
The Algonkian Era. 
Mr. C. D. Walcott has established a lower limit for the 
Cambrian rocks, which if: applied in this district will place 
some of the dolomytes and quartzytes of the Silver Peak quad- 
rangle in the Algonkian. He writes: *““At present I draw the 
basal line of the Cambrian in Utah and Nevada at the bottom 
of the arenaceous shale carrying the Olenellus fauna. This 
refers to the quartzyte and siliceous shales of the Wasatch and 
similar sections, including that of the Eureka district, and that 
of the Highland range of Nevada, to the Algonkian Period 
(Era). On this basis, the dolomyte, quartzyte and the green 
knotted schists, underlying the Olenellus zone, north of the 
Clayton valley, must be called of Algonkian age. This might 
apply as well to some of the quartzyte and quartz-schist im- 
inediately west of the village of Silver Peak, and to the basal 
dolomyte generally of the Mineral Ridge, as well to some sim- 
ilar rocks, south of Cow Camp. 
The Paleozoic Era. 
Lower Cambrian. In the mountains north of Clayton val- 
ley and in those to the south-east crossed by the road from 
Silver Peak to Lida valley, and also in the Silver Peak range, 
Lower Cambrian rocks form large areas. The section north of 
Clayton valley shows at the base, a massive dolomyte, next 
a massive green quartzyte, both barren of fossils, with over- 
lying knotted schists, then Archeocyathus limestone and green 
Olenellus slate with dark limestone and some quartzyte and 
thin bedded slate near the top of the series, the general dip 
of which is here to the east. 
Along Barrel Spring ravine by the side of the Lida road, 
an even better section may be seen. Here the rocks dip south- 
east for a distance of two miles, at an average angle of 25 
degrees. Fossils are found in nearly all parts of this section 
* Am. Jour. Sci., Vol. 37, 189, pp. 374-392, 
