GEOLOGY. 217 



of the cretaceous formation of the Missouri. The upper 

 sub-divisions, which I shall have occasion to establish further 

 up, and that are not sufficiently distinct here, will complete 

 an account of this interesting formation. 



" On quitting Huppan-kutey Prairie, the entrance to the 

 Wassisha, or Vermilion River, and that of the Riviere 

 Jacques of the French, the Tchan-sansan of the Sioux, are 

 passed by in succession. In tliis interval, tlie valley liills are 

 at a distance, and the cretaceous formation is not easily fol- 

 lowed up ; but, a little further on, it re-appears on tlie left 

 side, with the plateau dividing the waters that empty into the 

 Tchan-sansan from those that flow into the Missouri. This 

 upland is known as the ' Coteau des Prairies du Missouri,' 

 or, more shortly, ' Coteau du Missouri.' 



" The elevated prairies that crown the right bank of the Mis- 

 souri River, rise gradually in the direction of the Rocky Moun- 

 tains, forming the northern extremity of those steppes, more ap- 

 propriately designated the American Desert. Hence, it will be 

 perceived that the river has its bed deeply incased in a valley, 

 flanked on the left side by the Coteau du Missouri, and on 

 the right by the American Desert. Over a length of 235 

 miles, comprised within this valley, between the Ni-obrarah, 

 or ' Eau-qui-court' river, and Fort Pierre Chouteau, the cre- 

 taceous formation exhibits its fullest development. It may 

 be satisfactorily examined at many places within this range ; 

 but a perfect representation of the whole of them may be 

 obtained, if, taking as a basis the description previously given 

 of Dixon's Blufi", there be added to it the modification pre- 

 sented by some of its new members. 



*' I may be permitted to think that this cretaceous forma- 

 tion is destined to occupy a conspicuous place in the history 

 of American geology ; and, as I am not aware that any details 

 concerning it are recorded, I shall now, to tlie exclusion of 



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