54 GEOLOGY OF THE HIGH PLATEAUS. 



plateau summits is rarely so great as 3°; the inclination of the structure- 

 slopes of the Basin Ranges is rarely so little as 8° or 10 D . 



As bearing upon the general hypothesis that the great structural feat- 

 ures are produced by the action of tangential forces generated by the secu- 

 lar contraction of the earth's interior, it may be remarked that the displace- 

 ments of the Plateau Province do not furnish any evidence of the operation 

 of such forces. A careful study of the system of the Kaibabs and High 

 Plateaus has established the conviction that in those districts no such force 

 has operated. Evidence, however, is often discerned that the strata, while 

 undergoing displacement, have been subject to tension arising from the 

 increased length of profile caused by the undulations so produced. This 

 lengthening of profiles in the vicinity of the monoclinals is indicated by 

 the repetitive faults with an oblique hade or underlie; and sometimes also 

 by the dropping of a long wedge of strata between two faults with con- 

 verging hades. Complications of this character often appear as super- 

 imposed features upon the great monoclinal flexures. 



