WHITE.] DISPLACEMENTS. 41 



scope with their distance from the main axis, and diverge or sweep 

 around to the southeastward as they stretuh away from the Uinta Mount- 

 ains. Although there is a greater or less degree of divergence of these 

 subordinate axes of flexure, they have neither a common origin nor a 

 common radial center in either of the two mountain systems ; but the 

 position of some of them, at least, shows equally intimate relations with 

 both. There are within this district three of these subordinate flex- 

 ures or uplifts which have intimate relations with the Uinta system, and 

 that have received distinctive names, besides two peculiar isolated 

 mountain upthrnsts, all of which will be described separately on fol- 

 lowing pages. These are the Plateau, Midland, and Raven Park Uplifts, 

 and Junction and Yampa Mountain upthrusts, all of which are shown iu 

 their relative positions in the sections at the bottom of the geological 

 map accompanying this report. 



UPLIFTS AND UPTHRUSTS.* 



The Axial Uplift. — This term is applied to the main flexure of the 

 Uinta system. The general course of the axis of this flexure through the 

 northern portion of this district is eastward, with a broad curve, the 

 concavity of which is to the southward. Its course is plainly indicated 

 on the geological map by the outcrops of the formations that border 

 both the eastern and western portions of Axial Basin. 



Upon reaching the eastern borders of this district the Axial Flexure 

 bends quite abruptly to the southward, and is lost among the hills that 

 lie to the eastward of Agency Park, which are a part of the foot-hills of 

 the Park Range of mountains. A short branch of the Axial Flexure sep- 

 arates from the main portion at the eastern border of the district, and 

 turns abruptly in a direction a little west of northward, passing near 

 Caiion Park, and blends with the general uplift of strata as they rise 

 toward the foot-bills of the Park Range, north of Yampa River. 



Judging from the phenomena now presented by the eastern end of 

 the Axial Uplift, it seems probable that at least the portion of it which 

 lies within and adjacent to this district was at first a simple, approx- 

 imately uniform, upward flexure; and that while a part of it remained 

 as originally flexed, those portions that now form the mountains were 

 more or less sharply uplifted from the remainder, the added displacement 

 amounting to thousands of feet. We find that the axis of the main 

 Uinta uplift is prolonged eastward from the eastern end of that mount- 

 ain range as a comparatively slight flexure of Cretaceous strata, which 

 blends with those of the Park Range foot-hills, as before described^ and 

 that the mountains of the Uinta system are composed of those strata 

 only that have been thus sharply uplifted, although the latter have suf- 

 ferred immense erosion since their elevation. Possibly they would have 

 suffered still greater erosion if it were not that the uplift has brought up 

 the comparatively hard Carboniferous strata, and those of the still harder 

 Weber quartzite, so high that they now constitute the visible i^ortion 

 of the whole mountain range. The amount of displacement embraced 



*Iu using the terms " uplift" and " upthrust," I do not thereby intend to express 

 any opinion as to the actual direction of movement in the displacement of the strata, 

 "whether upward or downward. The terms, especially the first, will be readily under- 

 Btood, and it seems more convenient for the reader and investigator to regard, at least 

 tentatively, the lower, which is the larger mass, as the fixed one; and the higher, 

 which are relatively the smaller masses, as those th^t have been uplifted. The term 

 " upthrust," so far as I am aware, has not been used before. Its applicability will 

 plainly appear in the following descriptions of the displacements of Junction and 

 STampa Mountains. 



