552 DEAN E. WINCHESTER 
Slim Buttes (Fig. 1): (1) in Reva Gap (Fig. 2), where the inclina- 
tion is about 30° from the horizontal; (2) one-half mile south of the 
Old L Ranch (Fig. 4), where the inclination is about the same as 
in Reva Gap; (3) at the northwest angle of Flat Top Butte, where 
the inclination of beds is about 20°. In each case the inclined beds 
are overlain horizontally by a thick, characteristic sandstone, 
whose age is not definitely known but which has been doubtfully 
Fic. 2.—Butte in Reva Gap. Height of cross-bedded portion about 75 feet 
referred by Darton to the Arikaree formation (Miocene). The 
strata beneath this sandstone include clay, marl, and sandstone, as 
shown in Fig. 3, in which fossils of Oligocene age are abundant. 
These, in turn, rest unconformably upon the lignite-bearing rocks 
of the region. 
If the inclination of the beds in the White River formation is 
due to a disturbance of the strata, which occurred at the close of 
White River time, that inclination should also be evident in the 
underlying rocks of the immediate vicinity, but such is not the case, 
as is proven by the following facts: 
*N. H. Darton, ‘Geology and Underground Waters of South Dakota,’’ Water 
Supply Paper, U.S. Geol. Survey, No. 227 (1909), p. 21. 
