550 C. R. KEYES — PROFILES AND STRUCTURES IN DESERT RANGES 



given by King,^ Gil^^ert/ Spurr/^ and others, at once discloses the fact 

 that there is a general independence of mountain profile and geologic 

 structure. This feature is still more impressive in the field. Concerning 

 this point, Lauterback^s discussion of the Humboldt Mountains and their 

 structure has a special bearing.^^ 



TYPES OF ANCIENT STRUCTURES OF THE BASIN RANGES 



Some of the more frequently occurring t3rpes of geologic structures 

 which the Basin ranges present may be especially noted for the reason 

 that, notwithstanding the great variety displayed, there appears to be so 

 little direct or genetic relationship existing between the tectonics and the 

 configuration of the mountains. It is to be noted that the several flexed 

 types are all of the most open character. It is a significant fact that in 

 nearly all of the original representations of the geologic cross-sections 

 the actual presence of faults is so rarely recognized. This doubtless 

 arises from several obvious and distinct causes. It is for such reasons 



Figure 1. — Gross-section of the Humtoldt Range 



as these that Dana,^^ after exhaustively reviewing the literature of the 

 subject in all its various phases, was led to the conclusion that the fault 

 hypothesis of Basin Eange structures was insufficiently supported by the 

 data published. 



Field investigations recently carried on seem to demonstrate that in 

 the cases of many of the ranges in which faults have been wholly un- 

 represented in the diagrams dislocations are not only actually present, 

 but some of them are of great throw. These faults are not necessarily 

 normal ones. It now seems quite possible that some of them at least 

 may be thrusts, which also originally reared mountains. The entire 

 provincial geologic column being made up of hard and brittle rocks, the 

 zones of shearing would be very thin and the angles of the planes with 

 the horizontal very high. 



8 U. S. Geological Survey of the 40tli Parallel, vol. i, p. 451 et seq. 



» U. S. Geological and Geographical Survey West of the 100th Meridian, vol. iii, p. 27. 



i<» Bulletin of the Geological Society of America, vol. 12, pis. 24 and 25. 



"• Bulletin of the Geological Society of America, vol. 15, 1904, pp. 289-346. 



^ Manual of Geology, fourth edition. 



