690 



INDEX TO THE STRATIGEAPHY OF NORTH AMERICA. 



The grounds for distinguishing the Eagle, Claggett, Judith River, and Bearpaw 

 formations as divisions of the Montana group are fully stated, their correlations are 

 discussed, and special reports on the faunas and the flora are presented. 



The distribution of the Cretaceous and early Tertiary in eastern Montana is 

 shown as determined by the special surveys of coal fields" and reconnaissances 

 connecting them. 



Notes relating to the development of the sequence in particular fields (Lewis- 

 town coal field. Crazy Mountains, Livingston district, and Great Falls coal field) 

 are given elsewhere in this chapter. 



For the northeast side of the Bighorn Basin, Washburne*®^ determined the 

 following section of the Cretaceous. (For Tertiary, see p. 775.) 



Cretaceous rocks on northeast side of BigJiorn Basin. 



» The evidence is not sufficient to class this formation as undoubted Laramie, consequently the term is used through- 

 out this report in a questionable sense. 



In the wide basin southeast of the Bighorn Mountains near longitude 106° 

 and latitude 43° the general section of the Cretaceous is, according to Shaw: ^^°* 



Cretaceous: 



Montana — upper two-thirds principally sandstone with coal; lower third dark shale with no coal. 

 Colorado — mostly dark-brown shale with some brown sandstone layers, and at the top a buff to 



white sandstone, which may be Niobrara, Near the base is the Mowry member, a very resistant 



dark shale which weathers white. 

 Cloverly — massive, brown, resistant sandstone, which commonly forms a pronounced hogback. 



Near the top there is some shale, and at the bottom a fine conglomerate. 



a Bull. U. S. Geol. Survey No. 316, 1907; No. 341, 1909. 



