T. W. Stanton — Fox Hills Sandstone. 173 



Stone. The three areas, though separated by intervals of 100 

 to 150 miles, all belong to the same general region, throughout 

 whicli it is evident that closely similar conditions prevailed in 

 the closing stages of the Cretaceous. 



Standing Rock and Cheyenne River Indian Reservations. 



A detailed description of this area will be given by Mr. Cal- 

 vert and his assistants in a report whicli is in preparation. For 

 the present purpose it is only necessary to direct attention to a 

 few points. The area lies on the west side of the Missouri 

 River between Cheyenne Kiver on the south and Cannonball 

 River on the north and it is divided into three approximately 

 equal parts by Moreau and Grand Rivers, tributaries to the 

 Missouri from the west. 



The rocks are little disturbed and usually appear horizontal 

 in ordinary exposures, but a more general study of their dis- 

 tribution shows that they dip a few feet in the mile toward 

 the north or northwest. The lowest formation exposed is the 

 Pierre shale, the upper part of which is seen in the valleys of 

 all the streams mentioned except the Cannonball. Above the 

 Pierre is the Pox Hills sandstone in many places forming 

 bluffs for long distances along the streams. This is the highest 

 marine Cretaceous formation in the section. It extends up 

 the Missouri as far as old Fort Rice, North Dakota, a few 

 miles above the Cannonball, and underlies the higher ground 

 in a broad belt of country southwest of that point. Overlying 

 the Fox Hills sandstone is the less resistant non-marine Lance 

 formation which in published reports has been called "Cera- 

 tops beds," " Laramie," " lower Foi't Union " and " somber 

 beds." It frequently forms badlands in the inter-stream areas 

 on the reservations and extends up the Missouri valley to Bis- 

 marck and beyond. As the streams have cut through both 

 the Lance formation and the Fox Hills sandstone for long dis- 

 tances, the relations between the two formations are easily 

 studied. 



The Fox Hills sandstone was first named by Meek and 

 Hayden* in 1861, who stated that it "is most distinctlj^ marked 

 at Fox Hills, between Cheyenne and Moreau Rivers, above 

 Fort Pierre." In the words of their description " this forma- 

 tion is generally more arenaceous than the Fort Pierre group, 

 and also differs in presenting a more yellowish or ferruginous 

 tinge. Towards the base it consists of sandy clays, but as we 

 ascend to the higher beds, we iind the arenaceous matter 

 inci'easing, so that at some places the whole passes into a sand- 

 stone. It is not separated by any strongly defined line of 

 demarcation from the formation below, the change from the 



*Proc. Acad. Nat. Sei. Phila., vol. xiii, pp. 419, 437. 



