UNKPAPA SANDSTONE AKD BEULAH SHALES 393 



Sandstone 3'ellovv, in place quite red, shaly at the 

 top, lower part massive 50 to 75 feet thick. 



Gray or marl gray and greenish with pink streak 

 near the middle, calcareous at base, with flint ; 

 includes an impure limestone with many fossils . 120 " " 



Eed beds. 



Unkpapa Sandstone 



This formation is always clearly separable both from the Sundance 

 shales below and the Beulah shales, or Lakota sandstone, above. It is 

 a massive, fine-grained sandstone, varying in color from white to purple 

 and buff. Its greatest development is in the foothill ridges or "hog- 

 backs " east of Hot Springs. Its first outcrops southward are observed 

 at Cascade Springs, and it extends continuously from that region past Hot 

 Springs all along the eastern side of the Hills, with its thickness dimin- 

 ishing north of Buffalo gap. Some of its exposures east of Hot Springs 

 are very striking in their brilliant coloring of pink, purple, and pure 

 white. The thickness is greatest in Shep's canyon southeast of Hot 

 Springs, where 225 feet were measured. In three of the canyons between 

 Fall river and Bufialo gap it has been quarried to some extent for build- 

 ing stone. One of these quarries is shown in figure 2, plate 43. Portions 

 of the rock are banded with various colors in the most beautiful manner, 

 in part along the stratification planes, but often diagonal to them. In 

 the quarry west of Buffalo gap these banded beds exhibit minute fault- 

 ing, affording fine illustrations of block fault phenomena. The sandstone 

 is characterized in general by its fine grain and ^-ery massive but uniform 

 texture. Contacts with the overlying bufi" sandstone of the Lakota for- 

 mation are frequently exposed, and they are seen to be marked by con- 

 siderable unconformity by erosion (see plates 43 and 44). 



Beulah Shales 



This Jurassic member has been designated the Atlantosaurus beds by 

 Marsh and others, but recently Mr W. P. Jenney,* in describing some 

 of the overlying formations in the northern Hills, has named it the 

 Beulah shales. It is a member that has yielded the remains of a num- 

 ber of large saurians collected by Professor Marsh on the north side of 

 Piedmont butte. This formation was regarded by Marsh as unques- 

 tionably Jurassic in age, a view which has been generally accepted. 

 The Beulah shales first make their appearance northwest of Hermosa, 



*19th Annual Keport of the U. S. Geological Survey, part II, p. 593. 



