654 NORTH AMERICAN INDEX FOSSILS. 



Upper Cretacic or Laramian. 

 Middle Cretacic or Montanan. 



Fox Hill series. 



Pierre series. 



Lower Cretacic or Coloradoan. 

 Niobrara series. 

 Benton series. 

 Dakota sandstone (upper). 



At the base of the Benton series lies the Dakota sandstone, 

 which marks a period of emergence, followed by one of sub- 

 mergence.** The upper part of this sandstone must be considered 

 an integral part of the Coloradoan, while the lower part in Kansas, 

 etc., is believed to be of upper Comanchic (Washita) age. 



In southern Alberta, the Montanan is divided into the Bearpaiv, 

 ludith River and Claggett formations, the last resting on upper 

 Coloradoan Cardium sandstone. The Bearpaw is succeeded by the 

 Edmonton. These formations are all more or less non-marine, 

 especially the Judith River (Belly River) formation. The Bear- 

 paw is of upper Pierre and Fox Hills age. Elsewhere in Canada 

 and in northwestern United States the Bear River formation of 

 non-marine origin, represents the whole or a part of the Colo- 

 radoan. The Livingston of Montana (3,300 ft.) is separated from 

 the lower Laramie by an unconformity. In central Colorado this 

 horizon is represented by the Ruhy formation (3,500 ft.) with 

 sometimes the Ohio formation (200 ft.) at its base. In the Front 

 Range region of Colorado, the Laramie is disconformably suc- 

 ceeded by the Arapaho series (600 ft.) and this by the Denver 

 (1,400 ft.), which is in part volcanic. All of these formations are 

 non-marine, or with some brackish water beds intercalated (lower 

 Livingston formation). 



In the Big Horn Mountains the following subdivisions of the 

 Cretacic have been made (Darton) : 



Upper Cretacic. 

 Laramian. 



DeSmet formation 5,ooo ft. 



** Grabau, A. W., Bull. Geol. Soc. of America, Vol. 17, p. 620. 



