W. Upham—Minnesota Valley in the Ice Age. 35 
* and next north and northeast to the Mississippi at Fort Snell- 
ing, its length being about two hundred and fifty miles. Its 
width varies from one to four miles, and its depth is from one 
hundred to two hundred and twenty-five feet. The country 
through which it lies, as far as Carver, about twenty-five miles 
above its junction with the Mississippi, is a nearly level expanse 
of till, only moderately undulating, with no prominent hills or 
notable depressions, excepting this deep channel and those 
formed by its tributary streams. Below Carver it intersects a 
belt of terminal moraine, composed of hilly till. Its entire 
course is through a region of unmodified drift, which has no 
exposures of solid rock upon its surface. 
Bluffs in slopes from twenty to forty degrees, and rising one 
hundred to two hundred feet to the general level of the coun- 
try, form the sides of this trough-like valley. They have been 
produced by the washing away of their base, leaving the upper 
portions to fall down and thus take its steep slopes. The river 
in deepening its channel has been constantly changing its 
‘distance, 
The Minnesota valley in many places cuts through the sheet 
