48 r. W. SARDESON SAINT ANTHONY PALLS 



the river above the falls in its earlier stages. Excepting for the artificial 

 dam above the falls, the river there might be 15 feet lower than it was in 

 earlier stages. Winchell had estimated that the limestone formation dips 

 15 feet from Fort Snelling to the falls, biit I am not able to find by using 

 the contour map of the U. S. Geological Survey that such is the case. 

 The lowering of the river above the present falls much rather began with 

 the joining of the Nicollet Island rapids and the rapids above the falls 

 and the consequent reducing of the upper limestone. This lowering 

 would be gradual. Very probably Father Hennepin saw the falls of 

 Saint Anthony (1680) before the river had cut all the upper limestone 

 from its bed, and possibly the change was not complete when Carver 

 (1766) saw it. The increased rate of recession of the falls, too, since 

 Carver's time, as calculated so nicely by Professor N. H. Winchell, may 

 be due to the changed condition of the falls and rapids. 



With the bed of the river resting on the top of the lower limestone 

 only, the last stage of the falls began. The manner of recession has be- 

 come a matter of historic record. While since 1871 the front of the falls 

 has been protected by an "apron," yet the recession had been well observed 

 before that time.^^ I have seen two breaks in the crest which have 

 occurred in the last few years. "It is not so much the excavation at the 

 foot of the falls that causes the recession as the excavation of the sand- 

 stone just below the lime rock by water that enters natural joints in the 

 rock and comes in contact with the crumbling sandrock, causing dislodge- 

 ment and final downthrow of large blocks."^^ Eecently caves formed 

 under the limestone and enlarged until the ledge fell. Blocks once thrown 

 down were farther lowered by eroding of the sandstone from under them 

 gradually, so that a block-covered rapids extended from the foot of the 

 falls to where the blocks had been brought as low as the undermining of 

 them could proceed. 



Conclusion 



As already stated, the Minnesota-Mississippi valley from above Fort 

 Snelling to Saint Paul is not a pre-Glacial valley, but a Glacial and post- 

 Glacial one, which was cut to its maximum depth by the river Warren, 

 in the same manner as the Saint Anthony gorge was made by the Missis- 

 sippi river. The recession of Saint Anthony falls may be taken as having 

 begun in a fall or rapid of the river Warren over 5 or 6 miles below the 

 confiuence of the Minnesota and Mississippi rivers. That fall ended 

 above the confluence on the river Warren in the Minnesota valley. The 



" See Annual Report Chief of Engineers to the Secretary of War for 1870, p. 278. 

 " Winchell : Op. cit, p. 340. 



