GEOLOGICAL CROSS-SECTIONS. 215 



as a precipitous wall, abutting against Carboniferous limestones, followed 

 by a great development of Nevada Devonian. The former are estimated 

 at 1,700 feet and the latter at 4,500 feet across the lower and middle mem- 

 bers of the Nevada series. At Basalt Peak igneous intrusions spread out east- 

 ward for 9,400 feet, concealing the sedimentary beds and completely obscur- 

 ing the structural features produced by the Rescue fault. Beneath these 

 basalts the section is constructed wholly upon observed data, both to the south 

 and east, and will be understood by reference to the map. From here to the 

 end of the atlas sheet basalt flows or Quaternary accumulations cover every- 

 thing with the exception of two outcrops one, easterly-dipping beds of 

 Weber conglomerate, almost wholly encircled by igneous rocks, and the 

 other, a low, gentle swell of Carboniferous limestones, rising out of the 

 valley deposits not much above the base level of the sections. 



section GH-iK. This section (atlas sheets ix and x) is drawn across the 

 southern end of the mountains in a continuous line from west to east, pass- 

 ing through Grays Peak, Gray Fox Peak, Carbon Ridge, and Century Peak, 

 and crossing at right angles the Hoosac, Pinto, and Rescue faults. It 

 crosses the mountains about 4 miles south of section CD-EF, and for the 

 most part runs along the extreme southern end of the different mountain 

 blocks, touching, however, the Fish Creek Mountains at their northern end, 

 but passing far to the south of the Diamond Range. The section passes 

 along the base of the Mahogany Hills, following the Lone Mountain lime- 

 stones approximately parallel with their strike, the beds dipping northward 

 into the hills beneath the Nevada Devonian. Across Spring Valley, for a 

 width of 6,000 feet, all Paleozoic strata are concealed beneath the Quater- 

 nary, but with the rising of the hills on the east side the Pogonip lime- 

 stones come in capped on the summit of the ridge by the Eureka quartz- 

 ites. Here the broad anticlinal structure of the Fish Creek Mountains is 

 clearly brought out, but without the fault recognized on the east side of the 

 higher portion of the mountains. East of Castle Mountain there occurs a 

 shallow basin or depression in quartzite occupied by Lone Mountain and 

 Devonian beds, beyond which there is a second anticline, with the Eureka 

 beds arching over the summit. At Lamoureux Canyon occurs a slight dis- 

 placement, the walls on both sides where the section crosses exposing the 



