PALEOZOIC SEDIMENTARY SEMES 239 



confined to the Cambrian and Ordovician periods. The Lower Cambrian 

 beds are best seen in the northeast and southeast portions of the quad- 

 rangle. They are, however, well exposed on Mineral ridge west and 

 northwest of Silver Peak. The Upper Cambrian rocks, lying unconform- 

 ably on the Lower Cambrian, are best seen in the north end of the Silver 

 Peak range, near Emigrant pass. The Ordovician rocks appear to rest 

 conformably on the Upper Cambrian, forming one series, but have been 

 separated from them on account of the difference in age and lithological 

 differences. The Ordovician series is well developed in the Palmetto 

 mountains. Except where there are intrusions of granolites, the Paleozoic 

 rocks do not show much evidence of great disturbances before the period 

 of uplift of the present ranges, which was probably near the close of the 

 Tertiary era. 



LOWER CAMBRIAN 



The lowest Cambrian rocks are well seen in a remarkably fine section 

 in the southeast portion of the quadrangle in Barrel Spring ravine, by 

 the road from Silver Peak to Lida. From the mouth of the ravine up 

 which the Lida road goes, at the north base of the hills to the south edge 

 of the quadrangle, these rocks dip very evenly to the east of south at 

 angles from 20 to 50 degrees, the average dip being in the neighborhood 

 of 30 degrees. The lowest exposed beds are mica-slates and quartzites, 

 with some limestone layers containing well preserved Olenellus of large 

 size, more than one species of Archeocyathus, and other fossils, with a 

 higher horizon of green slates and limestone beds also containing Olenel- 

 lus 17 and in their upper portions little conical shells, probably Salterella. 

 A still better section of the basal Cambrian beds is to be found in the 

 hills north of Clayton valley. Here the base of the section is a dolomitic 

 limestone and marble, perhaps 2,500 feet in thickness, overlain by massive 

 quartzites and green knotted schists perhaps 4,000 feet in thickness. 

 Neither the dolomite nor the quartzite contain any fossil remains, but 

 underlie with apparent conformity the higher fossiliferous series. These 

 beds have already been referred to as being possibly of Algonkian age. 

 These knotted schists are seen under the microscope to be composed of 

 minute colorless grains, probably both quartz and feldspar, with very 

 abundant minute fibers nearly colorless, which seem to be sericite. The 

 knots are in part chlorite and in part aggregates of opaque grains. There 

 is a distinct schistosity, the dip being southwest at an angle of 30 degrees, 

 and obscure traces of an original sedimentary structure dipping east 

 55 degrees. The bedding planes of the knotted schists are conformable 



17 All of the Cambrian fossils from the Silver Peak quadrangle have been determined 

 by C. D. Walcott. 



XXI — Bull. Geol. Soc. Am., Vol. 20, 1908 



