j NICOLLET ISLAND RAPIDS 47 



As a result of this pronounced dip with the stream, the limestone ledge 

 which forms the crest of the fall rises above the bed of the river opposite 

 the lower end of Nicollet island, and at the upper end of the island it is 

 wholly above the river, the Saint Peter sandstone reaching some 20 feet 

 above the water level. The river channel on either side of Nicollet island 

 has been cut through the limestone formation and partly into the Saint 

 Peter sandstone. This condition extends up the river a fourth of a mile 

 I Jbeyond Nicollet island, where, as Winchell describes it, a drift-filled pre- 

 Glacial valley is met. The rise of the limestone is toward the side of that 

 valley. 



Briefly stated, the Mississippi river flows along the pre-Glacial valley 

 for some miles in a southerly direction to the mouth of Bassett creek. 

 The old valley continues in the direction of the creek, southwesterly, 

 while the river turns southeasterly over the side of that old valley. The 

 Mississippi river, at an early stage, must have encountered the limestone 

 which bordered the old valley, since the ledge was there at the present 

 820-foot contour line. There is indeed evidence of thickly deposited silts 

 to indicate that the Mississippi river and Bassett creek were impounded 

 back of the limestone ledge for a time. 



The river channel would encounter the limestone on its upturned edge, 

 and a rapids would soon result from such a barrier. As the river cut its 

 way obliquely through the limestone the rapids must pai-i passu descend 

 the river. At an early stage the river flowed in a rapids in part over the 

 now high and rocky upper end of Nicollet island, while in its last natural 

 stage (1856) I learn that the rapids began opposite the lower end of the 

 island, reaching thence to the falls. 



There has been evidently this Nicollet Island rapids descending the 

 river, cutting the limestone ledge at one edge, while Saint Anthony falls 

 ascended the river, cutting the ledge at the other. In its last stage Saint 

 Anthony falls has entered the reach of the Nicollet Island rapids. The 

 last stage is therefore very different from earlier ones. 



Saint Anthony Falls 



To the description of Saint Anthony falls I need add but little. This 

 fact should be noted, however, that the last stage of the falls differs as 

 compared to earlier stages in that the lower limestone remains alone, the 

 upper limestone having been cut away under the river by the Nicollet 

 Island rapids, into which the falls had receded. An artificial dam above 

 the falls now raises the water to about the level of the upper limestone — 

 that is, to 795 feet above tide — which appears to have been the height of 



