THE LARAMIE FORMATION AND THE SHOSHONE GROUP 37 



The Laramie may be defined as a formation of brackish or fresh- 

 water sandstones and shales, usually quartzose and coal-bearing, 

 which constitute the uppermost division of the conformable, consecu- 

 tive, and widespread series of the upper Cretaceous in the Rocky 

 Mountain and adjacent regions. It rests upon the Montana marine 

 group. The only upper limit now definitely known is a stratigraphic 

 break, above which comes, normally, some formation of the Shoshone 

 group. 



Should a series of sediments be discovered connecting in unbroken 

 sequence the Laramie and the lowest recognizable Shoshone forma- 

 tions, the boundary between them must be established at least for 

 that section, on the basis of facts which cannot be anticipated. 



By this definition the Laramie is inseparably connected with the 

 great Cretaceous section below it, as in the conceptions of King, 

 Hayden, and perhaps all of the earlier observers. It was presumably 

 coextensive with the Montana beds and represents conditions which 

 had existed locally during the Judith River epoch in Montana. 



While the Laramie was originally so widespread, its distribution 

 as now preserved, is a matter of much uncertainty. Veatch reports 

 6500 feet of Laramie strata below the horizon marking the break 

 at the base of the Carbon beds and no doubt other developments of 

 the Laramie occur in Wyoming, though recent investigations make 

 it necessary to refer many supposed Laramie exposures of that 

 State to the Shoshone group, and to study carefully all sections before 

 making assignments. 



The Laramie is exhibited in its typical relations in the Denver 

 basin and northward along the base of the Front Range. It there 

 rests conformably on the Fox Hills (Eldridge) and is succeeded by 

 a stratigraphic break representing a long period of erosion, as dem- 

 onstrated by the materials of the basal conglomerate of the Arapahoe 

 formation. The remaining Laramie of the Denver basin varies 

 from 600 to 1200 feet in thickness. The greater part of the known 

 Laramie flora has been found in this district in the coal measures 

 near the base of the formation. 



Further discussion of Laramie distribution seems inadvisable at 

 this time for the reason that the information gathered by many 

 parties of the U. S. Geological Survey engaged in studying the coal 

 measures of the Rocky Mountain region, under direction of M. R. 

 Campbell, cannot as yet be utilized. 



