72 STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 



the later work, exigencies made necessary the study of economically 

 important districts and the temporary ignoring of intervening dis- 

 tricts. The column was divided for descriptive purposes, largely 

 on the basis of lithology and local names were introduced, which 

 were utilized in other districts, but not always in the same sense. 

 At an early date, the difficulty in determining boundaries of forma- 

 tions at the west was recognized ; the Fox Hills and the Pierre were 

 combined as the Montana and the Niobrara and Fort Benton as the 

 Colorado. In this study, the Meek and Hayden classification is 

 employed as it is based on palseontological ground and enables one 

 to recognize changes in physical geography. As modified by later 

 studies it is 



Laramie 



Montana } " 



Pierre 



J Niobrara 



Colorado , „ 



[ Benton 



Dakota 



Kootenai. 



Each of the several formations is coal-bearing in areas of greater 

 or less extent, but barren or nearly so in others of greater extent. 

 They will be described in the order of age. Literature dealing with 

 the coals of the western Cretaceous is voluminous, but it consists 

 largely of preliminary studies with land classification as the object. 

 Much of the region is very sparsely settled, as it is agriculturally 

 arid, and systematic mining is confined to narrow strips along the 

 railways. For the most part, explorers must depend on natural 

 exposures, which are indefinite. At the same time, one cannot re- 

 frain from grateful acknowledgment of the skill exhibited by not a 

 few of the observers, for the mass of information is so great as to 

 prove an embarrassment in preparation of this review. 



The Laramie, Lance, Edmonton. 



The post-Cretaceous erosion spared only scattered areas of 

 Laramie in the southern districts, but farther north, where the region 

 of orogenic disturbance was restricted more and more to the far 



