3o8 A. E. PATH 



difference of nearly 2,000 feet in altitude cannot be due to difference! 

 in erosion alone. Moreover, the Granite Mountains now sho\ 

 smooth surfaces, whereas the Ferris and Seminoe mountains are 

 rough and rugged, a difference which indicates that the Ferris anc 

 Seminoe mountains are in a more youthful stage of erosion. 



From these differences in altitude and in character of topog- 

 raphy, therefore, it appears clear that the present Ferris and 

 Seminoe mountains are younger than the Granite Mountains. 

 This conclusion further indicates that the Ferris and Seminoe 

 mountains are probably the result of a relatively late readjustment 

 along the south margin of the Sweetwater uplift, and, from the 

 nature of the structural features in this region, that this later 

 deformation was a slight overthrust in which the Sweetwater area 

 moved southward toward the Rawlins uplift. 



How much later in geologic time than the main development 

 of the Sweetwater and Rawlins uplifts this readjustment took place 

 is not readily ascertainable. From unpublished field information 

 pertaining to T. 28 N., Rs. 90 to 95 W., along the south edge of 

 the Sweetwater uplift, gathered by Hares just beyond the south 

 margin of the area covered in his report on "Anticlines in Central 

 Wyoming,"^ and by Smith along the north margin of the area 

 covered in his report on "The Eastern Part of the Great Divide 

 Coal Field, Wyoming,"^ it is clear that there has been considerable 

 readjustment in these townships since pre-Wasatch time, when 

 the major upfolds were first developed. The significant evidence 

 along this marginal zone is to be found in the nearly flat-lying 

 Tertiary formations (Wasatch ?) in the Green and Crooks moun- 

 tains, at altitudes of 1,000 feet or more above the nearly flat-lying 

 Tertiary beds (Wind River and White River formations) of the 

 basin that now marks the Sweetwater uplift. It is also an interest- 

 ing fact that the White River (Oligocene) formation of the Sweet- 

 water basin — the "sea" in which the Granite Mountains stand out 

 as "islands" — seems to be limited on the south by the fault zone 

 that marks the boundary between the pre-Cambrian rocks of the 

 Sweetwater uplift and the Paleozoic and Mesozoic formations in 



' C. J. Hares, op. at., pp. 233-79. 



' E. E. Smith, U.S. Geol. Survey Bull. 341, pp. 220-42. 



