38 



THE GLACIAL LAKE AGASSIZ. 



On the Minnesota division of" the Chicago and Northwestern Railway 

 the traveler going west enters the inner moraine belt of the Coteau at the 

 west edge of jMuniesota, a little east of Gary, about 1,450 feet above the 

 sea (fig. 8). The line crosses this belt obliquely, occupying about 4 miles, 

 and ascending' some 200 feet. Then 6 miles are moderately rolling, mainly 

 in smooth swells; and the next 6 miles, lying- partly on each side of Alta- 

 mont, are among the knolls and small hills of the outer moraine, 1,750 to 

 1,950 feet above the sea; succeeded by a smooth, slightly undulating- area 

 of till, which rises to the summit of this line near Goodwin, 2,000 feet 

 above the sea, extends thence nearly level to Kranzburg, and then descends 

 250 feet by a very gradual slope to Watertowu. 



:^ Branches of lAC ,g 

 5 <fui Par/e /9. ^ 



-Section across the Coteau dea Prairies in Yellow Medicine County, Minn., and Deuel and Codi] 

 S. Dak. Horizontal scale, 12 miles to an inch ; vertical scale, 1,000 feet to an inch. 



ton counties, 



The altitude of the Coteau des Prairies is due to the Upper Cretaceous 

 formations, here spared and left by preglacial erosion as a broad and higli 

 ridge, upon which the drift deposits lie, rather than to extraordinary thick- 

 ness of the drift lievond that which it commonly has on the lowlands at 

 each side The knolls and hillocks of the morainic belts rise 20 to 60 and 

 rarely 75 or 100 feet above the intervening hollows, and the thickness which 

 they add to the drift sheet of the Coteau des Prairies appears to be from 50 

 to 150 feet. That the prominence of this highland is not due to these 

 morainic accumulations is shown in South Dakota at Goodwin and farther 

 north by the greater elevation that is reached within a distance of 2 to 5 

 miles by the smooth sheet of till at their west side, which there foi-ms the 

 watershed and beyond descends to the Big Sioux River. 



Nearly a constant elevation, varving between 1,950 and 2,050 feet 

 above the sea, is maintained along the entire northern half of the Coteau 



