222 J. E. SPURR — ORIGIN AND STRUCTURE OF THE BASIN RANGES 



Peoquop range. — Mr King * describes the Peoquop range as showing 

 through most of its extent a monoclinal dip ; but in the southern por- 

 tion of the range this apparent monocline is seen to be really one of the 

 limbs of a distinct syncline, and this syncline gives place to an adjacent 

 anticline in the region of Antelope buttes. 



For the same reason as above stated, in the case of the Gosiute moun- 

 tains, we may infer that the Peoquop range owes its form mainly to long 

 continued erosion. 



• Humboldt range. — The Humboldt range f has as its principal structural 

 feature a great anticlinal fold, which strikes ap])roximately parallel with 

 the range. The northern portion of the range has a central core of 

 Archean schists and granites, from which the Paleozoic rocks dip away 

 on both sides. From Fremont pass southward to Hastings pass the 

 range is entirely made up of these Paleozoic rocks, which are separated 

 from the Archean area to the north by a great fault at Fremont pass. 

 Mr King states that the eastern face of the range from Fremont pass 

 northward to Eagle lake is the result of a powerful fault by which the 

 dislocated eastern half of the anticlinal fold has sunk out of sight. 



The fault which King notes at Fremont pass (and which has also been 

 observed from the base of the range by the present writer) is transverse 

 to the general trend of the mountains or a))proximately east and west. 

 The vertical dis[)lacement is enormous, the Carljoniferous and Devonian 

 rocks on the south abutting against the granite and Arcliean on the 

 north. There is, however, no scarp, only the transverse gap which has 

 been called Fremont pass. The mountains to the north are, to be sure, 

 higher and more rugged than those to the south, but not at all in pro- 

 portion to the amount of differential uplift, and wliat difference there is 

 is evidently due to the greater resistance to erosion of the granitic rocks 

 as compared with the softer Paleozoic strata. The writer suspects that 

 a north-and-south fault lies along the west base of the range, by which 

 the Silurian rocks are brought uj) against the Carboniferous. If this 

 fault exists, the relatively downthrown side forms the mountains, while 

 the upthrown part lies in the valley. Aside from these considerations, 

 the whole rugged and deeply dissected topography bespeaks long con- 

 tinued erosion. The governing anticlinal structure of the range is easily 

 explained, for the core consists of granites and quartzites, which are more 

 resistant than the limestones which overlie, so that the center of the 

 fold when completely denuded still forms the most conspicuous topo- 

 graphical feature and determines the main ridge. 



* Ibid. 



t King: Op. cit., p. 738. 



