GEOLOGY OF THE KILDEER MOUNTAINS 267 
tain no fossils.” From the upper beds Cope collected several 
fossils of vertebrates, including species of Aceratherium and Oreo- 
don. Leonard describes these beds as “conspicuous, snow white 
elevations.”? Further he continues: ‘‘The White River group is 
here composed of white clays at the bottom, on which rests a coarse 
sandstone which in places is filled with large pebbles; this is over- 
lain by about 1oo feet of calcareous clays which in turn are over- 
lain by more than 1oo feet of fine-grained, greenish sandstone.” 
From the calcareous clays he reports the finding of an Eporeodon 
major skull. Earl Douglass? reports Mesohippus, Aceratherium, 
Ictops, and Merycoidodon fossils from the beds at White Butte. 
The remains are fragmentary and scarce, but enough fossils have 
been found to place the beds without question in the White River 
formation. 
In the same report Douglass reports Oligocene strata at the 
Little Badlands 26 miles northeast of White Butte and about 14 
miles southwest of Dickinson. The section of the beds which he 
gives is similar to that of White Butte; there also he found enough 
fossils to identify the beds as of the White River formation. 
The strata at the top of Sentinel Butte belong probably to the 
Oligocene series. They are composed of light-gray calcareous clay 
or.marl, which contains toward the top beds of a nearly white, com- 
pact limestone. These beds contain fossil fishes which are not 
closely related to any previously described; therefore, by means 
of these, Plioplarchus whitei Cope, and Plioplarchus sexpinosus 
Cope, no correlation is possible. Sentinel Butte is about 40 miles 
west of northwest of the Little Badlands and about the same dis- 
tance north of northwest of White Butte (Fig. 1). 
The Killdeer Mountains are about 50 miles northwest of Sentinel 
Butte and about 45 miles north of the Little Badlands. Sentinel 
Butte is part of the divide between the Little Missouri River and 
its tributary on the west, Beaver Creek; with one exception it is 
1 E. D. Cope, Proc. Amer. Phil. Soc., XXI (1883), 216-17. 
2 A. G. Leonard, Geol. Surv. North Dakota, 5th Bien. Rpt. (1908), p. 65. 
3 Earl Douglass, Annals Carnegie Mus., V, Nos. 2 and 3 (1909), pp. 281 ff. 
4C. A. White, Amer. Jour. Sct., 3d Ser., XXV (1883), 411-16; A. G. Leonard, Geol. 
Surv. North Dakota, 5th Bien. Rpt. (1908), p. 64. 
