52 F. W. SARDESON SAINT ANTHONY FALLS 



for a distance of over 2 miles. The fall possibly approached the cascade 

 type, as seen in the ilinnehaha falls now, where the limestone stands in 

 an overhanging ledge from which the stream makes a clear leap to the 

 bottom of the gorge. The recession of Minnehaha falls depends on the 

 weathering down of the shaly contact between the Saint Peter sandstone 

 and the limestone. The limestone then scales off in small pieces, from 

 the base upward, and the sandstone washes slowly away, so that a ledge 

 remains upon which a pony can be ridden under the falls. 



The gorge from Saint Paul to Fort Snelling is still more uncertain. 

 In a more general comparison it may be said that we have represented 

 in these gorges three periods or units. From Saint Paul (representing 

 locally the beginning of ice-retreat) to the Soldier gorge above Fort 

 Snelling is one unit; from the Soldier gorge (representing the time of 

 the glaciers' retreat from the head of the Mississippi) to the Lake Street 

 stage is a second unit; from Lake street (representing the time of falling 

 off of lake Agassiz and river Warren) to the present is a third unit. If 

 the last is 10,000 years, the other two may be each no less, giving 20,000 

 years as the duration of the river Warren and 30,000 years as the lapse of 

 time since the glaciers decamped from Fort Snelling. 



