SYSTEM OF PLATEAU FAULTS. 27 



a part through shearing. In any case the effect is in its broader aspects 

 the same. One side has been uphfted, the other side " thrown." 



The true monocHnal in its perfect form is much more common in the 

 sedimentary than in the volcanic beds The latter seem to lack that flexi- 

 bility or rather adaptability which enables strata to undergo differential 

 distortion without fracture. In the sedimentaries, on the other hand, the 

 monoclinal seems to be the favored form of displacement, though trenchant 

 faults are common enough. In the volcanics there is a tendency to the 

 monoclinal form, but the unyielding nature of the rocks has produced com- 

 minuted fracture in places where a monoclinal would doubtless have been 

 produced had the strata been more compliant. Hence the volcanics seldom 

 preserve the vmbroken monoclinal, though there is one good example of this 

 preservation. This comminution is a source of perplexity in resolving the 

 displacement into its constituents, and frequently renders it necessary to 

 stay long and scrutinize abundantly before the extent of it and its true 

 method can be properly ascertained. 



Another striking characteristic of these displacements is their sys- 

 tematic arrangement. Viewed in one way they approach parallelism, but 

 there is a noticeable convergence of the lines as we trace them from south 

 to north. In disturbed regions the faults and flexures usually tend to paral- 

 lelism, and while the tendency is as decided here as it is elsewhere, yet the con- 

 verging tendency is a noticeable characteristic. These great displacements 

 of the High Plateaus are the northward continuations of those which have 

 been described by Powell and Gilbert in the vicinity of, and crossing, the Col- 

 rado River at the Grand Canon. But in the Grand Canon district (where 

 they gave origin to the Kaibabs) the belt of faulted country is wider and 

 the intervals between the faults and flexures are greater than in the High 

 Plateaus. This width diminishes northward, and several of the grander 

 faults at length become merged into one vast monoclinal flexure, forming 

 the western flank of the Wasatch Plateau. South of the Colorado these 

 faults have not been studied, but the indications now are that they also 

 converge in that direction, giving the greatest expansion to the nystem just 

 where the Colorado cuts across it. It is impossible to separate the faults of 

 the High Plateaus from their systematic association with those of the Kai- 



