522 .1. G. LEONARD 



counties. In this area west of the river outcrops are not uncommon, 

 and thus the region is the most favorable in the state for the study 

 of the older drift sheet. 



The following account of some oi the features of the pre- 

 Wisconsin drift is based on observations made during the course 

 of field work for the North Dakota Geological Survey, a portion of 

 the time in co-operation with the United States Geological Survey, 

 in Morton, Dunn, Mckenzie. Burleigh, and other counties during 

 the years 1000 to 0)14 inclusive. 



The older drift west of the Missouri is in most places thin and 

 has undergone great erosion. The deposit perhaps never had 

 any considerable thickness in this region except locally, where it 

 forms moraines, and much of the glacial material which was 

 formerly present has been swept away by streams. The drift 

 throughout much oi the area is thus represented by bowlders and 

 gravel, the coarser materials left behind when the finer debris, 

 such as clay and sand, was carried off. There are extensive tracts 

 where little or no glacial material is present and where only an 

 occasional bowlder or a patch oi gravel indicates that the ice sheet 

 once covered this region. The western margin of the older drift 

 is therefore poorly defined, and the mapping of it is based largely 

 on the distribution of glacial bowlders and gravel. 



As would be expected from the foregoing characters, the pre- 

 Wisconsin drift has not, except in certain restricted areas, affected 

 the topography to any large extent. The region is one of main- 

 streams and mature drainage, in striking contrast with the area 

 of the Wisconsin drift, with its few streams, numerous lakes, and 

 youthful topography. 



PRE-W ISOOXSIX DRIFT OF BURLEIGH COUNTS 



Fast of the Missouri River in Burleigh County, between the 

 river and the Altamont Moraine, the older drift is present, but the 

 occasional outcrops appear to indicate that it forms only a thin 

 veneer over the underlying rocks, seldom exceeding S or 10 feet in 

 thickness. It outcrops in the bluffs of the Missouri River 3 miles 

 northwest of Bismarck, where 10 feet of till is found, and in the cut 

 at the east end oi the Northern Pacific bridge it attains a thickness 



