5i6 



A. G. LEONARD 



the Fox Hills formation. Their thickness is about 200 feet and 

 they are well exposed in the river bluff south of Brockton. As a 

 rule the sandstone is soft, but in places there are hard concretion- 

 like masses, which after weathering stand out as ledges or as 

 cannon-ball shaped masses imbedded in a matrix of softer rock. 

 The material shows much irregularity of bedding, is in places 

 cross-bedded, and is extremely variable in character horizontally. 



Fig. 3. — The Fox Hills formitio.i on Hell Creek, Montana, showing 

 ledge (A) near the top. 



Wmsm 



sandstone 



The Fox Hills sandstone probably occurs also about the Pierre 

 shale area in southeastern Custer County, Montana. 



The variability of the Fox Hills formation is well illustrated by 

 the foregoing description of its outcrops. In some places, it is 

 composed wholly of sandstone, in others it is mostly a sandy shale, 

 while in still others it is partly sandstone and partly shale. When 

 shales are present they are generally arenaceous and are commonly 



