546 D. F. HEWETT 



The relations between the beds described above, which may be 

 referred to as the border Wasatch, to the Bighorn Basin Wasatch 

 might be uncertain if it were not for the existence of remnants on 

 hilltops in several parts of the border belt. These remnants have 

 the same lithologic features as the border Wasatch and some of the 

 beds rather high in the section of the Bighorn Basin Wasatch in the 

 Tatman Mountain section. A longitudinal section through three 

 of these remnants from a point south of Sunshine northeast toward 

 the basin shows that they are part of a river channel which extended 

 from the foothills of the border belt out into the basin with a 

 gradient of 25 to 70 feet to the mile. It is the writer's opinion 

 that the border Wasatch was laid down at the same time as some 

 of the beds that make up the Lost Cabin or Tatman Mountain 

 beds (upper Wind River) of Sinclair and Granger in the central 

 part of Bighorn Basin. The particular significance of the border 

 Wasatch beds is that they indicate that there has been little if any 

 local folding of the Cretaceous and Fort Union beds of the border 

 belt since upper Wind River beds were laid down. The border 

 Wasatch has, however, been broadly warped and locally faulted. 



Only tentative conclusions concerning the age and correlation 

 of the stratified tuffs and breccias that overlie the border Wasatch 

 can be made at this time. In considering this problem the writer 

 has had the benefit of informal discussion with Dr. J. P. Iddings, 

 who examined a large part of the area of the Yellowstone Park 

 (11) and that covered by the Absaroka folio (10). 



It may be recalled that along the headwaters of Lamar River 

 (Cache Creek) and Clark's Fork (Republic Creek) several varieties 

 of light colored andesitic tuffs and breccias, locally distinctly 

 stratified, underlie the darker, basaltic breccias that cover a large 

 area east of Yellowstone River and Lake, and north of the latitude 

 of Greybull River (to). Although locally, the lower group ("early 

 acid breccias") appears to merge upward with the upper group 

 (''early basic breccias"), elsewhere there is evidence of considerable 

 erosion of the lower group before the deposition of the upper group. 

 The lower group yielded a large flora, considered by F. H. Knowlton 

 to be Fort Union (lower Eocene), whereas the flora of the upper 

 group, likewise large, is considered to be upper Miocene. From 



