GEOGRAPHIC STRUCTURE OF THE PLATEAU PROVINCE. 25 



upheaved by the production of a fault and part passu with the upheaval, 

 eroded into irregular forma and modified by flows of eruptive matter from 

 beneath. While this is the general structure throughout the region under 

 consideration, there are many exceptions, as indicated by Mr. Gilbert. Of 

 especial interest are the "uplifts limited by parallel faults (G), and to these 

 maybe assigned a few instances of isolated synclinals (D), occurring under 

 circumstances that preclude the idea that they are remnants omitted by 

 denudation," and the "many ranges built of faulted and dislocated rock- 

 masses (F) with an imperfect anticlinal arrangement." 



Perhaps the latter are what I have called Zones of Diverse Displace- 

 ment. 



In the northern portion of the province other modifications of the gen- 

 eral structure seem to appear. Mr. King, in the third volume of the "Geo- 

 logical Survey of the Fortieth Parallel," page 451, says: "These low mount- 

 ain chains which lie traced across the desert with a north and south trend 

 are ordinarily the tops of folds whose deep synclinal valleys are filled with 

 Tertiary and Quaternary detritus." 



That there should be exceptions to the general type of structure in this 

 province is not strange, for similar exceptions occur in each of the other 

 provinces, as will appear hereafter; but I have myself seen no true- anticlinal 



mountains in the Basin Province. 



\ 



The mountains of eruptive origin in this province are chiefly accessory 

 masses to the simple ridges of upheaval, and so far as my observations 

 extend, are of the Tu-shar type. 



OROGRAPHIC STRUCTURE OF THE PLATEAU PROVINCE. 



In the Plateau Province the Kaibab structure prevails, but other types 

 of structure are found. The Uinta Range, which furnishes the type for the 

 Uinta structure is found within this province, and a number of simple anti- 

 clinals have been discovered ; we have also found many Zones of Diverse 

 Displacement. 



The mountains of eruptive origin are of all the types above mentioned ; 

 table mountains have been observed in the region drained by the Grand, 

 White, and Yampa Rivers. Pilot Butte has already been mentioned, and 



