102 ANNALS NEW YORK ACADEMY OF SCIENCES 



canyon south of Parker Peak, lying on the Unkpapa sandstone. In Hell 

 Canyon the formation extends to within abont a mile of the Cheyenne 

 River. It is variable in thickness at this point and consists mainly of 

 gray and red sandy clay. On the west side of Falls Canyon the formation 

 is about 60 feet thick, greenish at the base, darker above, and light green, 

 and maroon in its upper portion ; on the east side it thins to about 20 feet. 



There are exposures of the Morrison in Chilson Canyon a mile south- 

 west of Chilson, and in the heads of branches of Bennett Canyon, where 

 it is pale greenish, massive clay, with thin, white, fine sandstone members 

 3 to 10 inches thick. It is also cut through by Cheyenne Eiver east of 

 Edgemont. In an exposure in Eed Canyon, where the formation is 80 

 feet thick, there is a thin limestone layer containing remains of algas at 

 the base. In a well at Edgemont the formation appears to be about 1 50 

 feet thick. "In the western part of the quadrangle the Morrison shale 

 is distinctly separated from the Sundance formation, and in the eastern 

 part from the Unkpapa sandstone, by an abrupt change in character and 

 material, but there is no evidence of erosional unconformity." 



The Morrison in the Sundance quadrangle has been described by Barton 

 (1905, 5). The formation here shows the usual light gray and maroon 

 colors, with buff and purple. It contains thin beds of sandstone and 

 occasional layers of limestone. The average thickness is about 150 feet. 

 The outcrops form a zone extending across the western and southwestern 

 parts of the quadrangle. The deposits are distinguished from those of 

 the Sundance by the color and massive texture of the shale. The most 

 outcrops are in the ridges adjoining Beaver Creek, along Mason Creek,. 

 in Skull Creek Valley north and west of the Holwell ranch, in Black 

 Canyon, along Oil Creek and in Oil Creek Valley. 



The following sections of the Morrison formation in the Black Hills 

 region are given by Darton, from O'Harra (1909, 5) : 



Section of Mon-ison Formation on north side of Sourdough Creek, 6 Miles 

 north of Hulett, Wyoming 



Feet 



Shale, yellow at top, red at bottom 18 



Black shale 14 



Black shale with 4-inch sandstone near top, slight purple or pink tinge 



throughout and rather conspicuous near the middle 17 



Black shale 26 



Slightly sandy green soft shale ; some lime nodules near base 10 



White sandstone 2 



Green shale 5 



White sandstone, carbonaceous streaks 2 



Gray and reddish shales 40 



134 



