2 2 A. G. LEONARD 



2,000 to 3,000 feet. Only locally has there been warping or folding 

 of the strata, as in the Cedar Creek anticline, which extends from 

 near Glendive, Montana, southeast into southwestern North 

 Dakota.^ This anticline was probably formed about the close of 

 Fort Union time and prior to the deposition of the White River beds. 



QUATERNARY SYSTEM 



Pleistocene deposits. — The Cretaceous and Tertiary formations 

 are largely buried beneath a mantle of Pleistocene deposits left 

 by the ice sheets which once covered the region. These deposits 

 conceal the bed rock except where they have been cut through by 

 streams, thus exposing to view the underlying formations. With 

 the exception of the Lake Agassiz silt of the Red River Valley the 

 Pleistocene deposits are not shown on the geologica Imap (p. 7). 

 but they cover the entire state, except the southwest corner. 

 The preglacial surface on which they rest had undergone great 

 erosion during the Tertiary period, as already stated, and was 

 therefore doubtless quite uneven and rough and cut by many 

 stream valleys. These surficial deposits rest on the Archean granite 

 and Paleozoic rocks in the Red River Valley; farther west they rest 

 on the Pierre and other Cretaceous formations, and in western 

 North Dakota they directly overlie the Tertiary strata. They 

 overlie the earlier formations without regard to altitude, the surface 

 on which they rest ranging in elevation from 450 to 2,500 feet above 

 sea-level. 



Glacial drift. — The only portion of the state which was not buried 

 beneath the Pleistocene ice sheets, and hence did not receive a 

 deposit of drift, is the southwest corner. The drift extends from 

 40 to 60 miles west and south of the Missouri River, though it is 

 here represented largely by gravel and bowlders, since the till is 

 thin and in scattered patches. 



There are at least two, and probably three, drift sheets in North 

 Dakota, namely. Late Wisconsin, Early Wisconsin, and an older 

 drift, which may be referred to provisionally as the Kansan, though 

 it may prove to be younger. The Late Wisconsin drift covers 



'A. G. Leonard, U.S. Geol. Survey, Bull. No. 285, 1906, p. 317; No. 316, 1907, 

 pp. 195, 203; W. R. Calvert, U.S. Geol. Survey, Bull. No. 471, 1912, p. 201. 



