114 HATCHER — OLIGOCENE AND MIOCENE DEPOSITS. [Aprils^ 



as to appear as conglomerates. Less frequently there are strata of 

 limestone. These are usually only an inch or two in thickness, 

 though occasionally attaining to as much as a foot. They are 

 always of quite limited extent laterally. 



The White River formation has been subdivided into the Titan- 

 otherium and Oreodon beds, the former at the base, the latter at 

 the top of the series. The Titanotherium beds have a maximum 

 thickness of about two hundred feet, and are composed of very fine, 

 white, reddish- or greenish-colored clays with numerous lenses of 

 sandstones and conglomerates, not faunally distinguishable, how- 

 ever, from the clays. The Oreodon beds, with apparently slight 

 local unconformities, immediately overlie the Titanotherium beds. 

 They have a maximum thickness of five hundred feet and consist 

 of brown or pinkish-colored clays, banded but usually not lamin- 

 ated except at one or two horizons where distinct lamination is 

 plainly visible. The clays of the Oreodon beds are interrupted by 

 sandstone lenses, though less frequently than are those of the 

 Titanotherium beds, and the sandstones of the upper series are 

 usually of a much finer grain than are those of the lower. Toward 

 the bottom of the Oreodon beds in the Bad Lands of South Dakota, 

 there is a series of sandstone lenses known as the Metamynodon 

 sandstones. These sandstones are faunally distinct from the sur- 

 rounding clays. At the top of the Oreodon beds in the same 

 region, these sandstone lenses are replaced by a second series very 

 similar lithologically to the first, but quite distinct faunally. These 

 upper sandstone lenses have been called the Protoceras sandstones. 

 Their fauna differs not only from that of the lower Metamynodon 

 sandstones, but from that of the adjoining clays as well. While 

 the Metamynodon and Protoceras sandstones are faunally quite 

 distinct, both from one another and from the adjoining and under- 

 lying clays, sandstones and conglomerates of the Oreodon and 

 Titanotherium beds, they are, in so far as is at present known, of 

 extremely local distribution. At present neither of these two series 

 of sandstones has been recognized outside of a very limited area in 

 the South Dakota Bad Lands. Here they appear as lenses marking 

 the course of an ancient river channel, that in Oligocene times 

 crossed these plains in a direction almost at right angles to the 

 present courses of the Cheyenne and White Rivers, now the two 

 principal streams of this immediate region. On the same horizon 

 with the Protoceras sandstones and contemporaneous with them in 



