AGE OF MISSOURI RIVER VALLEY 



297 



several borings made for the Northern Pacific Eailroad previous to the 

 building of its bridge across the river at Bismarck, from 70 to 80 feet of 

 silt and gravel were passed through before reaching the bedrock, and in 



Figure 1. — Map showing old Pleistocene Valleys of western North Dakota 



one boring a boulder was struck at a depth of about 50 feet below the 

 river bed. 



On the west side of the Missouri Valley, between Mandan and the 

 mouth of the Knife Eiver, there is a well developed terrace which in 

 places is a mile and more wide. This terrace has an elevation of 55 to 60 



