POST-CRETACEOUS HISTORY OF WESTERN WYOMING 213 



upon the soft Cretaceous and Tertiary beds, erosion has produced 

 only a maturely dissected surface (Fig. 26). In this district the 

 peneplain has been wholly destroyed, and it is improbable that 

 any of the summits now rise to its former elevation. 



In the moderately resistant limestones, sandstones, and inter- 

 bedded shales, which constitute the Paleozoic sequence, erosion 

 has proceeded much less rapidly than in the soft Mesozoic and 

 Tertiary formations. Thus where the former rise to the surface 

 we find them only maturely dissected into ramifying V-shaped 



Fig. 26. — Mature topography developed on weak Cretaceous and Eocene strata 

 along Fish Creek, near the Continental Divide. 



valleys separated by skeleton ridges, or, where folded, into parallel 

 mountains and valleys. The topography of the Gros Ventre 

 Range and of the west slope of the Teton Range, as well as of moun- 

 tains farther south along the state boundary, illustrates this phase 

 of topographic development. 



Erosion has had the least effect upon the hard, massive, and toler- 

 ably uniform granites and gneisses of the pre-Cambrian complex. 

 In the district under consideration there are but six localities where 

 these ancient rocks reach the surface, and in three they have merely 

 been uncovered in the bottoms of mountain canyons. The only 

 expansive outcrops at high elevations are those in the Teton, 



