CRETACEOUS AND TERTIARY FORMATIONS 



533 



same stratigraphic position as the Laramie formation, with which 

 they correspond in whole or in part. 



FORT UNION FORMATION 



The Fort Union is one of the most important and best known 

 formations of the Northwest. It covers a vast area east of the 

 Rocky Mountains, stretching from Wyoming to the Arctic Ocean 

 in the valley of the Mackenzie River, and including several Cana- 



Fig. 8.— Outcrop of Fort Union on Beaver Creek, northern Billings County, 

 showing ten coal beds. The thickest measures four feet, four inches. 



dian provinces, much of western North Dakota, eastern Montana, 

 northwestern South Dakota, and central and eastern Wyoming. 

 The name Fort Union was first used by Dr. F. V. Hayden in 

 1 86 1 to designate the group of strata, containing lignite beds, 

 in the country around Fort Union, at the mouth of the Yellowstone 

 River, and extending north into Canada and south to old Fort 

 Clark, on the Missouri River above Bismarck. It is a fresh- water 

 formation and is composed of clay shales alternating with soft, 

 rather fine-grained sandstone and containing many beds of lignite. 



