26 GEOLOGY OF THE SIGH PLATEAUS. 



really taken place, how they are related to each other, what dislocations 

 have been produced by them, and what are the present and what were 

 probably the former attitudes of the disturbed masses ; and yet there are 

 very few subjects in the range of geology so difficult to study. It seems as 

 if Nature were ashamed of her scars, and resorted to numberless tricks and 

 devices to hide them from sight ; here smoothing over the break and deftly 

 hiding it with a mantle of soil ; there confusing the inquisitive student by a 

 multiplicity, of perplexing forms, which are sure to worry if not to mislead 

 him ; and always shy of the truth. Throughout the greater part of the 

 Plateau Province, Nature is so poorly clad in the raiment of soil and vege- 

 tation and the earth is so well dissected by erosion that these features do 

 not easily escape the scrutiny of the determined and experienced investi- 

 gator. In the High Plateaus, however, the faults are less readily scruti- 

 nized than in some other parts of the province, though much more conspic- 

 uously displayed than in smoother and moister countries or than in countries 

 of more complicated structure. While I suspect that many minor faults 

 have escaped detection, I am confident that all of the grander ones have been 

 discovered and their principal features and relations unraveled. 



All of the greater displacements of the district present certain well- 

 marked habitudes. Most important among them is the strict homology of 

 the faults with monoclinal flexures. In truth, so close is the homology, that 

 we are justified in calling a monoclinal in some of its aspects a modified 

 fault. The onh T difference for structural purposes is that in the case of a 

 typical fault of the simplest form the shearing is along one plane, while in 

 the monoclinal the shearing lies between two planes. We have also cumu- 

 lative or repetitive or " step-faults,'' where the shearing is subdivided among 

 several planes. All have this in common, that the passage from the uplifted 

 to the lowest thrown side is through a verv narrow zone, which has its width 

 reduced to zero in the case of the single or simple fault, All of the great 

 lines of displacement assume all of these modifications in different parts of 

 their extent. In one place the fault is simple. A few miles farther along 

 its course it may become subdivided into a series of "step-faults;" still far- 

 ther on, into a perfect unbroken monoclinal ; it may be at another locality 

 a faulted nioiioelinal — a part of the displacement being through flexing and 



