130 GEOLOGY OF TUB EUREKA UISTRIOT. 



exceeding 20°, forming- the entire slope as far as tlie Lookout fault. There 

 is little doubt that this quartzite is correctly referred to the Silurian, 

 although no direct evidence exists. Nearly everywhere else the Eureka 

 quartzite may be determined upon structural grounds alone, but here the 

 entire body from Lookout Mountain to Pinnacle Peak has been uplifted 

 between two longitudinal faults, with limestones of different age brought 

 to the surface on opposite sides of the displacements and lying unconform- 

 ably against the quartzite. In contrast with the ([uartzite on the west side 

 of the Lookout fault, limestones form the east wall stretching southward 

 until beds on both sides of the fault are buried beneath volcanic lavas. 

 This body of limestone extends eastward until cut off by the fault, bring- 

 ing up the basal members of the Cambrian limestone of Prospect Ridge. 

 Between these two faults the beds are broken by iiregular outbursts of 

 andesites and in places have undergone considerable alteration, due to sol- 

 fataric action, the beds being frequently intersected by calcite and quartz in 

 narrow seams and veins. So much disturbed are the beds that structural 

 features are of little value, although it may be well to add tliat the general 

 dip is eastward. These limestones have been referred to the Pogonip, 

 although e-\ddence of their position is not in all respects satisfactory. 

 Obscure fragments of fossils may be obtained in a number of places, but 

 only in one was anything like a grouping of forms observed. This fauna 

 was collected on the west side of Sierra Canyon, nearly due south from 

 Surprise Peak and just west of the Prospect Mountain limestone, in dis- 

 tinctly bedded strata inclined at an angle of about 40° eastward. All the 

 species obtained have been found in the Pogonip limestones elsewhere, but 

 singularly enough they are all known in the Hamburg limestone, every 

 species having a wide vertical range. They probably I'epresent beds not 

 far from the base of the Pogonip and possibly should be referred to the 

 same horizon as the beds east of Lookout Mountain, although at the latter 

 locality the fauna distinctly indicates the Hamburg period. This refer- 

 ence to the Pogonip, however, is justified by the occurrence of undoubted 

 Silurian beds underlying Suiprise Peak: a further search would certainly 

 determine the question. 



