THE LARAMIE FORMATION AND THE SHOSHONE GROUP 7^;^ 



the monograph on the Denver Basin'' the terms Laramie and Post- 

 Laramie were again used with this significance. 



If it be conceded that the interests of stratigraphic nomenclature 

 will be best subserved by retaining the term Laramie for the beds 

 of the conformable Cretaceous section above the Montana group it 

 is plain that the nomenclature of the younger formations, usually 

 separated from the Laramie by stratigraphic break or unconformity, 

 which were included through misapprehension by King and others 

 in the original Laramie, should also be considered in this connection. 

 It is still my belief that the use of a new group term for these forma- 

 tions will greatly assist in clarifying the situation. The tentative 

 term Post-Laramie has but imperfectly served the purpose intended, 

 and is clearly unsuitable for permanent use. It appears to be left 

 for me to finally propose this new term. 



The uplift that terminated deposition of the conformable Creta- 

 ceous section was, as it seems to me, in the first degree epeirogenic, 

 aflfecting the Rocky Mountain region from Montana to southern 

 Colorado, with eyery probability that its influence was equally 

 marked far beyond the limits named, especially to the north and to 

 the south. Certain facts of observation, such as the great angular 

 unconformities below the Livingston and Carbon beds and the 

 stratigraphic break of equal magnitude below the Arapahoe forma- 

 tion, may be interpreted to indicate that pronounced orogenic uplifts 

 of as yet undetermined amount and extent were imposed upon the 

 greater movement. Such comparatively restricted uplifts have 

 occurred at various times and in different districts throughout the 

 Tertiary period. That the movement was not one of continuous 

 uplift may be almost taken for granted. Subsidence doubtless 

 occurred but there is no evidence of true marine conditions ensuing 

 after the Laramie epoch, as there was after the Judith River. If 

 subsidence produced brackish water conditions in post-Laramie 

 time it must have been of but local extent. 



Succeeding or in part synchronous with the Rocky Mountain 

 uplift there was erosion and resultant deposition in many basins 

 or on the slopes of the rising land. For such of these more or less 



'^ Geology of the Denver Basin, Colorado, by S. F. Emmons, Whitman 

 Cross and G. H. Eldridge. Mon. XXVII, U. S. Geol. Survey, 1896. 



