38 CROSS 



The Shoshone group may be defined as embracing the lacustrine, 

 fluviatile or terrestrial deposits, composed of detritus from the rising 

 land area of the Rocky Mountain province, formed between the 

 Laramie and Fort Union epochs. The group embraces beds which 

 have been commonly referred to as "Post-Laramie" or "Upper 

 Laramie" in the literature of recent years. Dana, in his Manual of 

 Geology, used the alternative terms "Upper Laramie" and " Denver 

 Group, " the latter being an inadmissible and confusing application 

 of Denver in a second, comprehensive sense. The name " Post- 

 Laramie" was proposed by me, as already pointed out, for the 

 formations now included in the Shoshone Group. 



Among the formations which may now be specified, on published 

 data, as belonging to the Shoshone group are the Arapahoe, Denver, 

 Middle Park, and Animas beds of Colorado; the Carbon and Evan- 

 ston beds of Wyoming; the Livingston beds of Montana. The 

 Converse County "Ceratops beds" of Wyoming and the Hell Creek 

 beds of Montana belong to this group, according to Barnum Brown, ^* 

 who calls them "Post-Laramie." 



Many of the formations of the Shoshone Group appear to have 

 been quite restricted in area. At least, they are now isolated and 

 correlation is as yet rather tentative. It is not yet known that the 

 Arapahoe beds of the Denver Basin, or any other particular deposit, 

 represent the earliest of these local formations. There is reason to 

 correlate, more or less closely, the Denver, Middle Park, Animas, 

 and Livingston beds, which consist largely of similar volcanic debris 

 and contain similar floras or faunas. But it cannot be assumed that 

 volcanic eruption was coextensive with the uplift of this period nor 

 that it did not begin during the Laramie; hence it is probable that 

 formations consisting of non-volcanic material were deposited in 

 some districts during the Denver epoch, and there may be volcanic 

 material in some Laramie strata. It is plain that before complete 

 correlations of permanent value can be made among the Shoshone 

 formations the stratigraphic relations must be thoroughly examined, 

 the fauna and flora of each local deposit must be carefully studied 

 in the light of stratigraphic evidence, and all elements brought into 

 harmony. Such investigation will necessarily take many years. 



" The Hell Creek Beds of the Upper Cretaceous of Montana. Bull. Ainer. 

 Mus. Nat. Hist., Vol. XXITT, 1907, pp. 823-845. 



