CRETACEOUS AND TERTIARY FORMATIONS 515 



time interval between the deposition of the sandstone and the 

 overlying Lance beds would be indicated by the eroded surface 

 of the Fox Hills. 



In the vicinity of Iron Bluffs, on the Yellowstone twelve miles 

 southwest of Glendive, Montana, the Pierre is overlain by 150 feet 

 of sandstones and shales, the age of which is in doubt, though the 

 beds have the stratigraphic position of the Fox Hills. The lower 

 seventy-five feet is composed of shales and sandstones while the 

 upper half is formed of a brownish sandstone. The only fossils 

 found in these beds at this locality are some plants, which are 

 too fragmentary to be identified. 



The Fox Hills sandstone is well exposed on Hell Creek, a trib- 

 utary of the Missouri River in northwestern Dawson County, 

 Montana. Lying above the dark gray Pierre shale, with its 

 fossiliferous concretions, are 100 feet of shales and sandstone 

 belonging to the Fox Hills. The formation is here composed of 

 light gray to yellow, more or less sandy shale, with some layers 

 of nearly pure sandstone. About eight feet below the top, there 

 is quite a persistent bed of fine-grained yellow sandstone with a 

 thickness of eleven feet (Fig. 3). The beds are lighter in color 

 and, for the most part, more sandy than the Pierre shale. From 

 concretions near the summit of the Fox Hills on Hell Creek, Mr. 

 Barnum Brown collected the following shells: 1 



Cardium (Protocardium) subquad- Lunatia concinna M. and H. 



ratum E. and S. Cylichna scitula? H. and M. 



Nucula cancellata M. and H. Baculites ovatus Say. 



Tellina scitula M. and H. Scaphites conradi Morton. 



Yoldia evansi M. and H. Chemnitzia cerithiformis M. and H. 



Crenella elegantula M. and H. Mactra ? nitidula M. and H. 



Piestochilus culbertsoni M. and H. Actaeon (Oligoptycha) concinnus M. 



Anchura (Drepanochilus) americana and H. 

 . E. and S. 



Along the Missouri River valley, over 100 miles northeast of 

 Hell Creek, and near the station of Brockton, on the Great Northern 

 Railroad yellow sandstones interstratified with gray clay are found 

 overlying the Pierre. 2 These beds are probably to be referred to 



1 Bull. Am. Mus. Nat. Hist., XXIII, 827. 



2 Carl D. Smith, Bull. U.S. Geol. Surv., No. 381, 38. 



