DETAILS OF THE J UFA. 159 



grayish marls were seen, and at one place in the valley of the Red Beds, 

 where there had been a local uplift, the summit of the red clays, with a bed 

 of gypsum 6 feet in thickness, was found to be overlaid conformably by 25 

 feet of greenish and reddish marls and shales and yellow sandstone — a rela- 

 tion similar to that already described on the western side of the Hills. At 

 the pass of Rapid Creek through the foothills, the cliffs are capped by a 

 heavy bed of the Dakota coarse sandstone, about 25 feet thick, stained 

 deeply red and containing many ferruginous masses. Below this sandstone 

 are about 200 feet of poorly exposed Jurassic beds resting upon the red 

 gypsiferous clays of the Red Beds. The Jurassic beds consist in their 

 upper part of shaly and soft sandstones, with clays or marls, and have 

 below a greater thickness of greenish, drab and -yellow marls or clays, 

 with some streaks of deep red, and a snowy white stratum of very soft, 

 argillaceous sandstone. This sandstone appears to be some 80 or 90 feet 

 in thickness, and can be traced by its vivid whiteness several miles north- 

 ward along the foothills. It weathers readily somewhat like a clay, and 

 is probably a local variation of some of the argillo-arenaceous beds . of 

 the formation. 



Near the pass of Box Elder Creek these same beds are seen in frag- 

 mentary exposures. At the pass of Elk Creek through the foothills, beneath 

 the usual capping of coarse sandstone, here 300 feet in thickness, there are 

 exposed about 175 feet of gray or greenish clays or marls containing con- 

 siderable limestone in thin bands but no fossil remains. In the pass of the 

 north branch of Bear Butte Creek there is a repetition of nearly the same 

 facts : a capping of Dakota sandstone, here 15 feet in thickness, underlaid 

 by 50 feet of dark gray and greenish marls or clays with a three-foot seam 

 of argillaceous limestone, and then a grassy slope with no exposures to the 

 red clays of the Red Valley below. 



From this place around the northeast corner of the Hills to the valley 

 of Spearfish Creek occasional outcrops of the drab clays are seen, but they 

 present no good exposition of the structure of the formation and the notes 

 on their exposures are scarcely worthy of quotation. 



In the center of the Red Valley, two miles east of Spearfish Creek, 

 rises a prominent butte, Joe Peak, capped by Cretaceous sandstone and 



