1893.] The Titanotherium Beds. 211 
characteristic of these three divisions will be pointed out and 
figured later in this article. 
THE OvERLYING BEDS. 
The Titanotherium beds are everywhere overlaid by the 
Oreodon beds, except where the latter have been removed by 
erosion. So far as noticed there are in the Bad Lands of §. 
Dakota no evidence of any unconformity between the Oreodon 
and Titanotherium beds, unless the sudden change from one 
fauna to another should be regarded as evidence of an uncon- 
formity or at least as indicating a considerable break in sedi- 
mentation between the two beds. ‘ 
Southwest of the Dakota Bad Lands in the extreme north- 
western portion of Nebraska there seems to be some evidence 
of an unconformity between the Titanotherium and Oreodon 
beds, or at least that for a considerable period immediately 
following the deposition of the Titanotherium beds, this region 
became dry land and that the Oreodon beds were subsequently 
laid down upon the eroded surface of the Titanotherium beds. 
At the extreme head of Cottonwood creek, a small tributary of 
White river, from the northwest, in the northwestern part of 
Dawes county, there is an isolated butte composed entirely of 
the Titanotherium beds and containing many Titanotherium 
bones. The different strata composing this butte are horizon- 
tal. About one mile south of this isolated butte is a range of 
bluffs of the characteristic Oreodon beds, containing numer- 
ous bones of Oreodon and other associated animals. 
In the first mentioned butte Titanotherium bones are found 
at the same altitude at which Oreodon bones occur in the 
bluffs to the south. Whether this occurrence of Titanothe- 
rium and Oreodon bones at the same altitude in quite adja- 
cent beds is due to the Oreodon beds having been deposited 
upon the eroded surface of the Titanotherium beds, or to 
differences in the level of the bottom of the lake, at the begin- 
ning of the Miocene period, could not be determined. The 
horizontal position of the strata composing the Titanotherium 
butte would seem to favor the first conclusion, since if these 
