DISPLACEMENT. 179 



and we have a faulted flexure to the south and an abrupt flexure to the 

 north; the southern branch, farther westward, becomes a simple flexure, 

 and the northern branch changes its course somewhat, so that the beds are 

 greatly warped; then it becomes a faulted flexure, and finally a clean fault. 



Thus the great Uinta block was uplifted, behaving in part as an integer 

 to the extent that it was separated by flexure and fracture from the adjacent 

 country, and as a body of minute parts as it was flexed along the axial line. 



We are interested to know at what rate this great uplift progressed. 

 The evidence bearing on this point is of three classes: first, that derived 

 from the character of the displacement itself; second, that derived from 

 degradation; and third, that derived from sedimentation. 



The displacement is partly by faulting, partly by flexing. A priori, it 

 would appear that whether any given displacement should be by faulting 

 or flexing would be determined by four conditions, severally or conjointly: 

 first, rate of displacement; second, constitution of the beds displaced, flexi- 

 ble and brittle beds being contrasted; third, the depth of the beds consid- 

 ered, for the deeply seated beds, being less free to move, would be more 

 liable to bend, and beds nearer the surface, being more free to move, more 

 liable to break; and fourth, the nature or application of the force producing 

 displacement. Observed facts show that two at least of these a priori condi- 

 tions, the second and third, are true conditions. Both Mr. Gilbert and myself 

 have observed in the transverse section of a displacement that the hard beds 

 have been broken and the soft beds bent, and I have elsewhere published 

 such a section. 



In a region of country visited by Mr. Gilbert during the past season, 

 he found that the displacement in one district was by faulting, and in an- 

 other by flexing. In the region of faulting there had been but little sub- 

 sequent degradation ; in the region of flexing, much subsequent degrada- 

 tion; and these conditions led Mr. Gilbert to the conclusion that the 

 depth of the beds below the general surface at the time of the displacement 

 had determined these characteristics, and in studying facts which had been 

 collected in other regions by myself, he was able to show that they also 

 lead to the same conclusions. The places where these facts were observed 

 are so widely spread throughout the Plateau Province that it will not ' be 



