CRETACEOUS AND TERTIARY FORMATIONS 



537 



the overlying clays to a red or salmon-pink color and in many 

 places to completely fuse them to slag-like masses. The beds of 

 clinker vary in thickness from five or six to forty feet, or over, 

 and some of them can be traced many miles in the bluffs bordering 

 the valleys and in the ridges and divides, while large numbers of 

 the lower buttes are capped with these protecting layers (Fig. n). 

 There are great numbers of excellent exposures of the Fort 



Fig. 12. — The Tepee Butte bluff of Little Missouri River, 584 feet high, showing 

 dark colored upper member and light colored typical Fort Union below. 



Union beds in the wide belt of badlands bordering the Little 

 Missouri valley from a few miles below Yule to the mouth of the 

 river, a distance of nearly 200 miles; numerous good outcrops are 

 also found in the exceedingly rough badlands which border the 

 Yellowstone on the east between Glendive and its mouth. While 

 outcrops are quite abundant throughout the region under dis- 

 cussion, nowhere are there such favorable conditions for the 

 study of the Fort Union formation as in the two areas just men- 

 tioned. 



