82 THE GLACIAL LAKE AGASSIZ. 



■ceous shales, 500 feet; the Fort Pierre formation, dark-gray and bluish 

 shales and plastic clays, 700 feet; the Niobrara formation, lead-gray 

 calcareous marl, passing down into light-yellowish and whitish limestone, 

 200 feet; the Fort Benton formation, dark -gray laminated shales and clays, 

 sometimes alternating near the upper part with seams and layers of soft 

 gray and light-colored limestone, 800 feet; and the Dakota formation, 

 yellowish, reddish, and occasionally white sandstone, with, at places, alter- 

 nations of various-colored shales and beds and seams of impure lignite, 400 

 feet. Leaves of dicotyledonous trees, including many genera still existing, 

 are found in the Dakota formation; also a few species of fresh-water or 

 brackish-water and marine shells. The formations here enumerated above 

 this are marine deposits, as shown by plentiful fossils throughout the 

 greater part of the series. 



More recent classifications by King, White, and Eldridge unite the 

 two members of this series next above the Dakota, naming them together 

 the Colorado formation; and in like manner the succeeding two still higher 

 are united and named the Montana formation.^ For the purpose of the 

 present chapter, however, it will be more convenient to use the older desig- 

 nations. 



In the South Saskatchewan basin. — North of the international boundary, 

 the development of these portions of the Cretaceous system in the region 

 of the Bow and Belly rivers, which unite to form the South Saskatchewan, 

 is reported by Dr. George M. Dawson as follows: The Fox Hills sandstone, 

 in some parts of the disti'ict well defined as a massive yellowish sandstone, 

 but inconstant, 80 feet; the Fort Pierre formation, neutral-gray or brown- 

 ish to nearly black shales, marine, 750 feet; the Belly River formation, an 

 extensive fresh-water and brackish-water series, consisting of sandy argil- 

 lites and sandstones, the upper portion characteristically pale in tint, the 

 lower generally darker and yellowish or brownish, probably of the same 

 age with the Niobrara formation, 910 feet; and lower dark shales, observed 

 on the upper part of Milk River, regarded as representing the Fort Benton 

 member of the Upper Missouri section, 800 feet. The lowest or Dakota 

 formation is not recognized in that district. Valuable beds of lig-nite are 



'C. A. White, "Correlation Papers — Cretaceous," U. S. Geological Survey, Bulletin No. 



