546 A. G. LEONARD 



Aceratherium, Elotherium ramosum, Oreodon, and Leptomeryx. The 

 white calcareous clay below the upper sandstone is now known to 

 carry fossils and the sand below this clay is probably to be included 

 with the White River group. Professor Cope, in common with 

 other geologists at that time, regarded the underlying beds as 

 belonging to the Laramie, but as already stated, they are now on 

 the evidence of their plant remains known to be Fort Union in age. 



Mr. Earl Douglass spent some time in the White Butte locality 

 during the summer of 1905, and has described in considerable 

 detail the beds occurring here. 1 



In the middle member or Oreodon beds, he found the following 

 fossils: Idops, Ischyromys, Palaeolagus, Merycoidodon culbertsoni, 

 Leptomeryx evansi, Mesohippus, Hyracodon, Gymnoptychus, Eumys, 

 and Aceratherium. 



Mr. Douglass discovered another deposit of White River beds 

 about thirty miles north and east of White Butte, in Stark County. 

 The area, which is known as the "Little Bad Lands," lies some 

 twelve to sixteen miles southwest of Dickinson. All three divisions 

 of the White River group are here present and a number of mamma- 

 lian bones were collected. 



The third locality in North Dakota where the Oligocene occurs 

 is on top of Sentinel Butte, in northern Billings County, near the 

 town of the same name. The beds are here seen resting con- 

 formably on the massive sandstone which forms the top of the 

 Fort Union. The beds occur only on the northern end of Sentinel 

 Butte and their maximum thickness is not over forty feet. They 

 are clearly the remnants left by the erosion of a thicker and more 

 extended formation which doubtless once covered a large area 

 in this region. Where the strata are exposed in a low mound 

 near the northwestern edge of the butte they are seen to be com- 

 posed of light gray calcareous clay or marl, which contains, toward 

 the top, beds of a nearly white, compact limestone. This lime- 

 stone breaks readily into thin layers one-eighth to one-quarter 

 of an inch thick, and some of the thicker layers become siliceous 

 toward the center. 



In one of the upper beds of this limestone are found the remains 

 of two species of fresh- water fishes. These fossil fishes were first 



" Annals of the Carnegie Museum, V, Nos. 2 and 3 (1909), 281-88. 



