540 A, G. LEONARD 



Feet Inches 



Coal 2 8 



Shale i 



Coal 8 



Shale, brown - 3 



Sandstone, and sandy shale, yellow 20 



Shale, brown , 6 



Coal 10 



Shale, brown 6 



Coal 1 6 



Shale, brown 2 



Coal 3 2 



Shale 1 



Coal 1 8 



Shale, yellow and dark gray 20 



Sandstone, yellow 49 6 



Coal 4 



Sandstone and sandy shale 1 3 



Shale, dark > 10 



Coal 1 8 



Sandstone, yellow, to river level 12 



Total S84 



The large number of coal beds occurring in the Fort Union is 

 well shown in the above section. The base of the section is prob- 

 ably not over 100 feet above the Lance beds, which disappear 

 beneath river level not many miles below. The outcrop thus 

 includes not only a large portion of the lower yellow and light 

 gray member of the Fort Union, but also about 183 feet of the 

 upper, dark-colored member. Where the uppermost beds of the 

 formation are found, as on top of such high buttes as Sentinel, 

 Flat Top, Bullion, and Black, they are seen to consist of a rather 

 hard sandstone 80 to 100 feet thick. This rock forms vertical 

 cliffs about the summits of these buttes, and huge blocks breaking 

 off from time to time accumulate at the base of the cliffs in great 

 talus heaps. On Sentinel Butte and the White Buttes, the White 

 River beds are seen resting directly on this uppermost sandstone 

 of the Fort Union. 



The maximum thickness of the Fort Union is not far from 1,000 

 feet in western North Dakota, but over most of the region it has 

 undergone great erosion and from large areas hundreds of feet 



