238 J. E. SPURR — ORIGIN AND STRUCTURE OP THE BASIN RANGKS 



Worthingtnn monntnin. — This is a single mountain, and would not be 

 mentioned except tliat it lias been described by Mr Gilbert/'^ It lies 

 northwest of the Pahranagat range, with which it is connected by a 

 series of hills. Mr Gilbert, apparently viewing it from its southern end, 

 sketched the structure as nearly horizontal.* The mountain rises with 

 the ordinar}^ degree of declivity from the desert valleys at its base, and 

 its slopes were believed b}'^ Mr Gilbert to indicate faults. He says: 



" I can conceive of no erosion that slionld have left this thin segment as the 

 remnant of an inclined table or of a fold. Its narrowness, its straightness, and 

 its isolation marked it as a mass of strata thrust npward between two faults, of 

 which the companion parts lie beneath the debris at its feet." 



The range was observed by the present writer at its northern end, and 

 a view was also obtained southward along its eastern face. The dip, 

 which at the southern end is nearly horizontal, with a slight easterly 

 inclination, becomes westerly farther north and increases gradually 

 until at the northern end, some 14 or 15 miles from the southern end, 

 it reaches 30 degrees and follows the general surface slope. Therefore 

 Mr Gilbert's reasons for assuming faults on both sides do not appl}^ to 

 the northern end, for, seen from the north, the mountain might be 

 explained by followers of the fault h3^pothesis as a faulted monocline ; 

 but the change in dip suggests that the mountain is i)artof an anticlinal 

 fold. It has been observed by the writer, and previously by Mr Clar- 

 ence King,t that many of the monoclinal ridges of the Great basin 

 belong to folds from which the other })arts have been removed by ero- 

 sion, and that very often, by following a range, a portion may be reached 

 where the whole fold is shown. 



Resume of ranges of southern Nevada. — The known evidence indicates 

 that the ranges of central southern Nevada are almost entirely due to 

 erosion, which has worked on a series of folded and faulted rocks so 

 strongly as to overcome any direct effects of deformation on the surface. 

 But on the margins of the region, in the Mormon range, and possibly in 

 the Spring Mountain range, there are features of relief which a}>pear to 

 be primarily due to deformation, expressed chiefly by folding and to a 

 less degree by faulting. The deformation which is expressed in the 

 topography is evidently younger than that which has been subdued. 



RANGES OF CALIFORNIA ADJACENT TO SOUTHERN NEVADA 



White Mountain range. — The White Mountain range shows several ad- 

 jacent folds broken by faults. J The chief fold, according to Mr Walcott, 



♦Surveys West of the Hundredth Meridian, vol. iii, Geology, p. .37. 



t Geological Explorations of the Fortieth Parallel, vol. i, p. 737, ete. 



JG. K. Gilbert : Wheeler Surveys West of the llundredtii ^Meridian, vol. iii, Geology, p. 34. 



C. D. Waleott : Am. Jour. Sei., :',d sen, vol. xliv, lS9;j, p. Itj'j. 



