Til 10 DAKOTA KMDGE. 179 



chapter, gives the Unver part of the Dakota group. Fuller seetious, tliough 

 still incomplete, were observed in the canon of the Cheyenne, but the com- 

 ponent beds were not measured in detail. The walls of the canon are in 

 places from GOO to 800 feet high, and they are composed in chief part of the 

 sandstones of the Dakota They are perpendicular except at the base, and 

 are there covered by debris, though a few glimpses are caught of soft 

 rock, probably belonging to the Jura. The exposed portion of the Dakota 

 is fully 500 feet in thickness and, allowing for waste above and conceal- 

 ment below, the group must be estimated to exceed that amount. It has its 

 usual character in the main, but in the upper part there is a fine example 

 of the quartzitic phase. In fact, a large portion of the higher part of the 

 plateau is quartzitic, and the preservation of the table is largely due to this 

 circumstance. 



On the surface of the plateau near Red Canon Creek there is much 

 fine drift composed largely of quartz grains and garnets. 



North of Minne Katta Creek the outcrop resumes its character of a 

 monoclinal ridge, and so continues all about the east and northeast sides 

 of the Hills. The dip finds here its maximum and ranges from 20° to 40° 

 or 45°. The formation exhibits no peculiar features except the occurrence 

 in the northeast of the variegated clays already referred to 



At the north where the Dakota Cliff runs westward parallel to Red- 

 water Creek the dip is only about five degrees and the exposure takes the 

 form of a plateau. Farther west it diminishes still more, except in the im- 

 mediate vicinity of the Bear Lodge range where the strata are upbent 

 about the trachyte mass. From the summit of Warren Peaks the tabular 

 character is plainly evident, and the plateau is seen to slope gently to the 

 east and north and west. It has not, however, a continuous surface, but is 

 deeply dissected by canons in every direction. Topographically it is 

 limited on the west by the valley of the Belle Fourche, but a dissevered 

 remnant is to be seen on the farther side, supporting on its surface the vol- 

 canic cones known as the Little Missouri Buttes. 



Wherever examined in this northern portion of the Hills the gi-oup has 

 its typical lithological character, but the thickness was nowhere seen to be 

 greater than 200 feet. The following section shows so much of the forma- 



