372 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



on Grand River, though within a few miles of one another, appear to show different 

 relations with western and eastern faunas. Cross ^^^^ quotes Girty as follows: 



Considering the Powell and Newberry collections together it is notable that they contain 

 a considerable number of species which may be called distinctive western types, as compared 

 with the Pennsylvanian fauna of Colorado and of the Mississippi VaUey. * * * In some 

 cases nothing at all closely related to the types indicated is known from the region to the east. 

 In other instances there are more or less similar species known which ai-e not yet regarded as 

 identical with western forms, although they may prove to be so. 



The collections from Moab consist entirely of typical Pennsylvanian species, lacking the 

 forms specified as characteristic of the far western areas. The distinctly Peimsylvanian forms 

 fourid at the junction of the Green and Grand occur, however, at Moab. The Sinbad VaUey 

 fauna is very closely related to that from Moab. 



In view of the fact that none of these collections can be considered as exhaustive for the 

 localities, numerical comparisons are more or less untrustworthy; yet the table brings out cer- 

 tain contrasts or resemblances which seem worthy of note. Out of 42 species represented in 

 the Powell and Newberry collections but 9 have been found at Moab, or in the Sinbad VaUey, 

 while out of 43 species obtained in these latter localities 29 are known from the Pennsylvanian 

 rocks of southwestern or central Colorado. 



On the basis of the fossil evidence alone there can be no hesitation in considering the Moab 

 and Sinbad Valley sections as belonging to the Hermosa formation rather than to the Aubrey, 

 as represented in the lower Grand River valley. 



J-L 13. WYOMING, NORTHERN COLORADO, AND SOUTH DAKOTA. 



The stratigraphy of the Carboniferous sequence in the Bighorn Mountains and 

 other ranges of Wyoming, and in the Black Hills has been summed up by Darton : ^^^ 



The Lower Carboniferous rocks are exposed principally in the Black Hills and Bighorn 

 uplifts, and a few small areas occur along the foot of the Front-Range, in Colorado. It is prob- 

 able that these rocks extend widely under the Great Plains, but no borings have gone deep 

 enough to reach them, except in eastern Kansas and southeastern Nebraska. 



In the Black HiUs the Mississippian is represented by two limestone formations, the Engle- 

 wood and the Pahasapa, both containing an abundance of characteristic fossils, those of the 

 Englewood being equivalent to the lowest Mississippian (Chouteau or Kanderhook) and the 

 Pahasapa equivalent to the Madison limestone of the northwest. Some Leperditia in the con- 

 cretions in red shale at the base of the Minnelusa are of a type characteristic of the Mississippian, 

 especially at about the horizon of the St. Louis limestone. It is possible that considerable of 

 the lower part of the [overlying] Minnelusa is also of Mississippian age, for it appears to be equiva- 

 lent to the HartviUe limestone. The Littlehorn limestone of the Bighorn uplift consists mainly 

 of a representative of the Madison and Pahasapa limestones, and doubtless the Englewood is 

 also included, but the upper hmit of rocks of Mississippian age in both uphfts has not yet been 

 ascertained. 



Further Retails concerning the Black Hills are given in another paper by 

 Darton ^^^^ as follows: 



[The Englewood hmestone] appears to extend continuously around the Black HUls, every- 

 where immediately underlying the Pahasapa limestone. It averages 20 to 30 feet in thickness 

 and presents frequent outcrops in the lower slopes of the limestone escarpment and in numerous 

 canyons. It merges rapidly into the overlying [Pahasapa] limestone, occasionally with a few 

 feet of impure buff limestone intervening. It is usually sharply separated from the [underljdng] 

 Deadwood formation, but only by a sudden'change in the nature of the materials. The Engle- 

 wood limestone is usually fossihferous, containing numerous corals and occasional shells. The 



