154 GEOLOGY OF THE EUllEKA DISTRICT. 



by Quaternary deposits. They measure over 2,000 feet. This sectiou was 

 made east of Sugar Loaf, where the underlying- limestones are exposed, 

 passing conformably beneath the broadest expansion of overlying shales. 

 The occiurence of this limestone is exceedingly fortunate, as upon it 

 rests the evidence of the position of the overlying shales, whereas, north of 

 Charcoal Canyon no limestones occur beneath the shale, and as the beds 

 trend to the northwest with a greater angle than the course of the Rescue 

 fault, the lower strata are cut off along the line of the displacement. Direct 

 evidence is wanting of the precise position of the beds lying next the 

 fault. From Silverado Canyon northward to Packer Basin the sti-ata dip 

 uniformly eastward. Charcoal Canyon, Ox Bow Canyon, and the other 

 di-ainage channels traversing the formation, fail to give any good sections 

 across the beds, as the valleys, though broad, are extremely shallow, with 

 the underlying rocks more or less covered with soil and gravel, derived from 

 the disintegration of the friable interbedded sandstones. The stream bed 

 coming from Packer Basin has eroded somewhat more deeply into the shale 

 formation, the beds lying more highly inclined, but shortly after leaving 

 the mountains it enters the tuffs which overlie the shales. 



Cliff Hills.— South of Silverado Hills, and separated from them by the 

 broad expanse of Fish Creek Valley, lies a low ridge designated Cliff Hills 

 on account of the mural-like escarpment which they present to the Quater- 

 nary plain. These hills have no direct topographical connection with the 

 Eureka Mountains and are referred to here only because they happen to 

 come in on the southeast corner of the map. By reference to atlas sheet 

 XII, their relations to the Eureka Mountains may be seen at a glance. Geo- 

 logically they are of great interest, as the White Pine shale, which has 

 been recognized over such limited areas, occurs here under conditions simi- 

 lar to those found east of Sugar Loaf. Low undulating ridges of shale and 

 sandstone formed of westerly dipping beds pass beneath a broad, flat-topped 

 body of pyroxene-andesite. It is this andesite which gives the cliff-like 

 appearance to the hills, the dark bare rocks presenting a forbidding aspect 

 as they rise above the desert valley. In their mode of occurrence and 

 petrographical habit these andesites closely resemble those of Richmond 

 Mountain, and show the same modification in color, density, and chemical 



