OF WESTERN NORTH AMERICA. 



71 



west. It immediately overlies throughout, conformably or uncon- 

 formably, the upper part of the Brule cla}^ or Leptauchenia zone. In 

 some places lithologically, and ,everywhere faunistically, it can be 

 divided into lower and upper levels. 



Synonymy. — The typical Gering formation of Darton, 1899, is at 

 Scotts Bluff, western Nebraska; the broad extension by Darton of 

 this formation to other localities is somewhat doubtful. The name 

 Gering formation as used by Darton, Hatcher, and Peterson probably 

 applies to noncontinuous river sandstones and conglomerates (maxi- 

 mum 200 feet), which are in a manner analogous to the ^'Titanothe- 

 rium,'\^'Metamynodon,^' and ^'Protoceras sandstones" that traverse 

 the lower Arikaree clays or finer beds and partly erode irregular chan- 

 nels in the upper Brule clay {Leptauchenia zone). This formation is 

 thus probably of the same age as the lower parts of the Arikaree, 

 Monroe Creek, and Rosebud. Its known fauna is very limited. The 

 so-called Gering of Hatcher and Peterson is in southeastern Wyo- 

 ming and northwestern Nebraska; in their section it is said to be 

 lithologically similar to the overlying Monroe Creek. 



The typical Arikaree formation of Darton, 1899, is at Pine Ridge 

 Bluffs, in South Dakota; whether or not this extends to southeast- 

 ern Wyoming rests on future paleontological correlation. The Ari- 

 karee as described and mapped by Darton would broadly include the 

 whole of the Rosebud formation of Matthew, as well as the Monroe 

 Creek and Harrison, and broadly cover the whole of the Miocene. The 

 entire Arikaree forma-tion of Darton consists of finer materials, whitish 

 or light-buff sandstones, more continuous and w^idespread, lying either 

 on the Gering formation or on the Brule clay. 



There remain to be compared, therefore, the faunae contained in two 

 sections about 95 miles apart east and west, probably continuous, sub- 

 stantially similar lithologically, and containing a substantially similar 

 fauna. This comparison is based on the valuable recent papers of 

 Peterson and Matthew (cit. supra). The local names Monroe Creek, 

 Harrison, and Rosebud may all be retained until the question of geo- 

 logic identity or dissimilarity can be settled. 



Approximate correlations of the Arilcaree formation. 





Westerly section: Southeastern Wyo- 

 ming and northwestern Nebraska. 

 Hatcher, 1902; Peterson, 1906. (See 

 fig. 13.) 



Easterly section: South Dakota, Por- 

 cupine Creek. Matthew, Gidlev, 1904; 

 Matthew, Thomson, 1906. (See fig. 

 12.) 



Upper division 



Lower division 



Upper part of Harrison 



[Lower part of Harrison 



Upper part of Monroe Creek 



] Lower part of Monroe Creek 

 (Gering of Hatcher and Peter- 

 \ son) . 



Upper part of Brule clay, or Lep- 

 tauchenia zone. 



Feet. 

 200 

 200 

 300 

 200 



150 



Upper part of Rosebud 



juower part of Rosebud 



Upper part of Brule clay, or Lep- 

 tauchenia zone. 



Feet. 

 a 250 



"250 



n Estimated. 



