230 J. E. SPURR — ORIGIN AND STRUCTURE OP THE BASIN RANGES 



above referred to transverse gaps several thousand feet deep, with tribu- 

 tary gulches, have been excavated. 



Rmime of structure of eastern central Nevada. — In ever}^ case which has 

 been described, except the last, the ranges appear to have been formed 

 chiefly by erosion. Synclinal ridges are frequent and faults not espe- 

 cially abundant. When faults liave been found to be present they 

 have no primary effect upon the topography, except in rare cases. In 

 general, indeed, they stand as witnesses of the greater power of erosion 

 by their lack of scarps, by the reversed scarps (that is, scarps where the 

 eminence is on the downthrown side of the fault), or by the deep gulches 

 which have been eroded along them. The Tertiary volcanic rocks wliich 

 are found in this region also show very deep erosion. 



The Hot Creek range belongs to an exceptional type, whose deforma- 

 tion features have apparently not been overbalanced by erosion, and this 

 is very likely due to ])rotection by overlying lavas, which have them- 

 selves suffered deep erosion. 



RANGES OF WESTERN CENTRAL NEVADA 



Toquiwa range. — Most of the Toquima range consists of Tertiar}^ vol- 

 canics, eroded so profoundl)' that in places (as near Belmont) dikes, 

 which were, perhaps, the feeders, are exposed. The stratified rocks, which 

 lie near Belmont and south of it, appear to be bent into an anticlinal fold, 

 which trends north and south. Along the axis of this is a minor valle3% 

 I)ro])abl,y one of erosion. 



We ma}^ conclude that this range owes its origin to differential ero- 

 sion plus vulcanism. 



Toyahe range. — This range lies immediatel}'' west of the Toquima range. 

 Its southern portion is entirely buried beneath immense flows of rluj'o- 

 lite. Farther north * the structure is a distinct anticlinal fold, running 

 nearly north and south. A little south of latitude 40 degrees this fold 

 is cut by an east-and-west fault. The axis of the anticlinal, according 

 to Mr Emmons,t has suffered from a pressure coming from a direction 

 different from that which originally formed it, so that it is curved and 

 the folds distorted. This deformation of the original north-and-south 

 fold is probably connected with the east-and-west faulting. At Ophir 

 canyon Mr Emmons noted a syncline adjacent and to the east of the 

 main anticline. 



The anticlinal structure is explained when we find that the rock ex- 

 posed along the axis of the fold is a heavy quartzite, more resistant than 

 the limestone which overlies. This structure, then, instead of indicating 



*King: Geological Explorations of the Fortieth Parallel, vol. i, p. 740. 

 tGeological Explorations of the Fortieth Parallel, vol. iii, Mining Industry, p. 32G. 



