VOLUME XXIII NUMBER 3 



THE 



JOURNAL OF GEOLOGY 



APRIL-MAY igi5 



POST-CRETACEOUS HISTORY OF THE MOUNTAINS OF 

 CENTRAL WESTERN WYOMING 



ELIOT BLACKWELDER 

 University of Wisconsin 



PART II 



Later Tertiary planation. — Whether or not the early Tertiary 

 formations ever covered the entire district, it is evident that they 

 have been stripped from large areas which they formerly occupied; 

 for scattered outliers are now situated several miles beyond the 

 edge of the continuous outcrop. It is also an obvious fact that 

 large quantities of the original Tertiary strata have been carried 

 away by erosion in the broad basins themselves. The deforma- 

 tion which succeeded the laying-down of the sediments, probably 

 about the middle of the Miocene, must have initiated a new cycle 

 of erosion, and subjected to denudation large tracts which had 

 previously been sites of aggradation. In later pages it v/ill be 

 shown that between the Miocene and the present there have been 

 several erosion cycles, and the interpretation of those cycles forms 

 an important part of this essay. The data for this must be 

 drawn largely from the features of the existing topography, now 

 to be considered. 



The central part of the Wind River Range is in reality a broad 

 dissected plateau 20-30 miles wide, surmounted by a narrow 

 axial range of sharp peaks. The plateau is no longer complete 



Vol. XXIII, No. 3 193 



