WHITE.] DISPLACEMENTS. 43 



ward, and neither this diameter nor the short one coincide with the di- 

 rection of the axis of the main uplift. Its independence of the great 

 axis, however, is not without some analogy in that of the Plateau Up- 

 lift and the Yampa Mountain Upthrust, for the main axis of the Uinta 

 system makes a broad bend to the northward opposite Yampa Plateau, 

 which the axis of the Plateau Uplift does not coincide with ; and it is 

 the short axis of the Yampa Mountain Upthrust, and not the long one, 

 that coincides approximately with the general direction of the main 

 Uinta axis. These diverse positions of the axes of the accessory uplifts 

 and upthrusts in relation to the main axis, as well as the separateness 

 of each of these displacements, seem to be in keeping with the assumed 

 superaddition to the primary Axial Uplift, as has been before sug- 

 gested. 



The amount of the relative upward displacement of the strata that 

 now constitute Junction Mountain is easily computed from the known 

 thickness of the intervening groups in that region. For example, the 

 top of the Weber quartzite, as seen in the canon which Yampa Eiver 

 has cut through Junction Mountain, has been raised to a height that is 

 about equal to that of the top of the Colorado Group, as it now exists 

 in immediate proximity, or the plane that its top would now occupy there 

 if it had not been removed by erosion. Therefore, the sum of the thick- 

 ness of the whole of the Carboniferous, the Jura-Trias, and the Dakota 

 and Colorado groups is equal to the entire upward displacement of the 

 strata that now constitute Junction Mountain, because all these groups 

 of strata intervene between the top of the Uinta sandstone and the top 

 of the Colorado group. The amount of this displacement is, therefore, 

 not less than 8,000 feet, as will be seen by referring to the thickness 

 that I have assigned to those groups in Chapter III. Such an extraor- 

 dinary displacement as this, and the no less extraordinarily small limit 

 within which it has been confined, seems to justify the use of the term 

 " upthrust," as distinguishing it from ordinary uplifts. 



The illustration of the manner of this upthrust that has been used, 

 by comparing it to the action of a dull punch upon a plate of iron, so 

 that the sides of the hole would be somewhat torn in places instead of 

 being everywhere cleanly cut, is appropriate, from the fact that at three 

 or four places upon the borders of the upthrust, and near or at the base 

 of the mountain, there are portions of Triassic strata that have been 

 separated in the upward movement, but have been dragged up and 

 thrown over backward, or otherwise tilted, and, as it were, caught in 

 the jaws of the fault. The position of some of these dragged portions 

 is shown upon the geological map. 



The illustration of the action of a dull punch that has just been used, 

 is still further applicable to the broadly-rounded surfaces of the uplifted 

 strata, producing a gentle quaquaversal dip from the center to near 

 the borders of the upthrust, where the dip becomes suddenly greater, 

 or a fault. The outline of the upthrust, as before remarked, is oval, and 

 the faulting seems to have taken place only, or mainly, at the sides. At 

 the ends, the strata appear not to be faulted, but only strongly iiexed. 



Yampa Mountain Upthrust. — The general description that has been 

 given of Junction Mountain, as to its origin and structure, will apply in 

 almost every particular to Yampa Mountain. The amount of displace- 

 ment which its strata have suffered in relation to those that immediately 

 surround the upthrust, is a little greater than that of Junction Mount- 

 ain, although the size of the Yampa Mountain Upthrust is a little 

 smaller than the other, and its position is somewhat remote from the 

 other mountain uplifts of the Uinta Kange. This mountain upthrust lies 



