492 CROSS AND HOWE — RED BEDS OF SOUTHWESTERN COLORADO 



are quite equivalent is to my mind less natural than to consider the 

 Lower Wyoming a group embracing the Fountain beds and the litho- 

 logically distinct " Creamy sandstone, 1 ' which Darton thinks is equivalent 

 with the Tensleep sandstone of the Big Horn mountains, Wyoming (7), 

 and which in any case deserves a special name. 



The Upper Wyoming of the Denver region embraces the remainder 

 of the Red bed section, and it is referred to the Trias by Emmons and 

 Eldridge. Darton, however, in his valuable discussion as to the corre- 

 lation of formations of the Black hills, Big Horn mountains, and the 

 Front range (7) presents reasons for supposing that the Upper Wyoming, 

 as developed near Denver, may be wholly referable to the Permian series. 

 This is based on stratigraphic relations and the belief that a limestone 

 occurring shortly above the " Creamy sandstone " is the equivalent of 

 the Minnekahta limestone of the Black hills, where it contains Ba kewellia 

 and Edmundia, forms apparently identical with those characteristic of 

 the so-called Permian of the Mississippi valley. 



Poorly preserved shells of similar appearance were found in a lime- 

 stone at Morrison. Darton believes that the Opeche and Minnekahta 

 (Permian) and theSpearfish (Triassic?) formations, distinguished by him 

 in the Black hills, extend southward through Wyoming into northern 

 Colorado, but as their exposures are not continuous, and as lithologic 

 details vary in the different areas of outcrop, he proposed Chugwater as a 

 group term, which is thus practically equivalent to Upper Wyoming. 

 Darton states that the upper or Triassic (?) portion of the Chugwater group 

 thins out and disappears before the Denver area of Red beds is reached* 

 leaving only the supposed Permian as present in the Morrison and 

 Golden sections especially described by Eldridge (11). 



From the brief review just given it appears that the Red bed section 

 of the Front Range foothills contains no member to be correlated with 

 the fossiliferous Triassic (Dolores) of the western portion of Colorado. 

 The views of Darton and the writer harmonize in referring the entire 

 Red bed sections of the Denver region and southward, at least to the 

 Canyon City embayment, to the Paleozoic. The Fountain beds seem to 

 me to be synchronous in origin with the Pennsylvanian formations of 

 the San Juan region. An unconformity separates each from the Missis- 

 sippian Carboniferous (Millsap or Ouray) and above each in apparent 

 conformable relation is a non-fossiliferous complex of Red beds. On the 

 west slope these are embraced in the Cutler formation, while at the base 

 of the Front range is the more variable section of the Wyoming group, 

 succeeding the Fountain. Thatlthe beds of the Wyoming group (exclud- 

 ing a possible Triassic portion) are coextensive with the group consisting 

 of the Molas, Hermosa, Rico, and Cutler formations of the San Juan is 

 of course not to be assumed. 



