X GEOLOGY OF THE HIGH PLATEAUS. 



zones of diverse displacement: these districts are broken into smaller 

 blocks by faults and flexures, and often the blocks have been excessively 

 tilted and warped in diverse directions. On the flanks of plateaus and 

 mountain systems of the Uinta type where monoclinal flexures occur mono- 

 clinal ridges are frequently seen The position of these monoclinal ridges 

 is frequently varied by the occurrence of transverse faults. Where a great 

 Kaibab, Uinta, or anticlinal upheaval is found broken by a transverse fault, 

 that portion of the grand upheaval which has the greater amplitude will 

 have its monoclinal ridges placed more distant from the axis of upheaval and 

 that portion which has the less amplitude will have its monoclinal ridges 

 nearer the axis. In this manner, by vertical movements in transverse 

 faulting, the monoclinal ridges may be placed back and forth from the axis 

 of grand upheaval in such a manner as to give the appearance of lateral 

 faulting, i. e., faulting in a horizontal direction. 



On the plateaus stand buttes, lone mountains, and groups of mountains. 



The buttes are mountain cameos, composed of horizontal strata with 

 escarped sides — they are mountains of circumdenudation. 



The mountains are composed in whole or in part of extravasated matter 

 and may be classed structurally under three types. 



I. Those having the Henry Mountain Structure — where the locus of vol- 



canic deposition is below the base level of degradation. 



II. Those liaving the Tushar Structure — where the locus of volcanic 



deposition is at the base level of degradation. 



III. Those having the Uimcaeet Structure — where the locus of extrava- 

 sation is above the base level of degradation. 



In the first, the mountains are composed in part of volcanic and in 

 part of sedimentary materials. The volcanic matter exists as laccolites, over 

 which sedimentary strata have extended in great mountain domes, but such 

 strata may have been carried away, more or less, by atmosplieric degra- 

 dation. In this class each mountain is a mass of volcanic material, with 

 sedimentary beds upon its flanks, and often these sedimentary beds extend 

 high up or even quite over the volcanic materials. 



In the second, the mountains are composed wholly of volcanic mate- 

 rials erected upon a base of sedimentary strata. The mass is composed of 



