268 TERENCE T. QUIRKE 
the highest point in the state, being 3,430 feet above sea-level. 
The other known remnants of the Oligocene formations lie near 
the top of the divide between the Little Missouri River and the 
eastward flowing tributaries of the Missouri. Starting at the 
Black Hills, South Dakota, and following the divide north one 
comes to the White River formation first in Slim Buttes, then 20 
miles farther north in the Cave Hills" deposits, which are only about 
40 miles south of the White River strata on White Butte. 
If one were to look for another remnant of the Oligocene beds 
to the north of the Black Hills he would continue logically in the 
direction of the known deposits, along the divide just outlined. 
‘If the Oligocene deposits once extended over the Killdeer district 
the elevation of these hills is such that they might well contain 
remnants of these deposits. The Killdeer Mountains are about 
3,200 feet high and contain a thickness of almost 400 feet of Oligo- 
cene-like beds. The beds on Sentinel Butte at an elevation of 
3,340 feet are only 4o feet thick. The thickness of the White Butte 
and Little Badlands deposits at lower elevations are about 320 
and 200 feet respectively. A still greater thickness of Oligocene 
deposits at the Killdeer Mountains is explained by the general 
northeastward dip of the Fort Union strata north of Dickinson, 
North Dakota. 
Because the deposits of the Killdeer Mountains are uncon- 
formable on the Fort Union formation, because they are similar 
in character to undoubted deposits of the White River formation 
less than 50 miles distant, and for physiographic reasons they are 
referred to the White River formation. 
Origin of the White River deposits —Professor Cope’ wrote of the 
discovery of the White Butte deposits as “the locality of a new 
lake of the White River epoch.”” ‘Todd’ considers the White River 
beds of South Dakota to be lake deposits. Earl Douglass says: 
I have little doubt that the upper Tertiary deposits in North Dakota were 
also deposited in broad valleys of erosion. Much of the material of the deposits 
came from areas of granite and quartzite rock. In the region of the Black 
Hills are the only outcrops of these rocks for hundreds of miles; this, connected. 
1 J. E. Todd, Geol. Surv. South Dakota, Bull. No. 2, p. 123. 
2). D. Cope; op: cit., p. 216. 3 J. E. Todd, op. cit., p. 60. 
