PHYSICAL GEOGRAPHY. 23 



eleven miles upon the river ; the upper rapids are about fifteen 

 miles in length. Mr. Schoolcraft, who considered, as did 

 Nicollet, the Lake Itasca to be the source, computed the 

 whole length of the river at 3,160 miles, or 264 more than 

 Nicollet. This, probably, was occasioned by the addition 

 of estimates not very accurate from point to point upon the 

 river, founded upon the reckoning of the boatmen. 



Major Long, who measured the height of the falls of St. 

 Anthony with a plumb-line, in 1817, states it to be sixteen 

 and a half feet. In this he agrees w4th Pike, who visited it 

 twelve years before him. Carver called it thirty feet. Hen- 

 nepin, the first European who saw and named it, in 1680, 

 says it is fifty or sixty feet high. For reasons hereafter 

 mentioned, in the historical part of these notes, full reliance 

 cannot be placed on Henepin. It may be, however, that the 

 ponderous body of water is gradually wearing away the stone 

 which makes the bed of the river before it falls, and that thus 

 the height is constantly diminishing ; or, by the falling of the 

 stone, and the consequent receding of the fall, the same 

 effect might be produced. It is stated, by Nicollet, I think, 

 that in a half mile the whole fall is seventy-five feet. 



In relation to the recession of the falls, and the whole 

 descent of the water, Mr. Keating says : — " The river (Mis- 

 sisippi) runs upon a bed of sandy alluvion, resulting from the 

 destruction of the bluffs, but in many places the rock is laid 

 bare. These observations upon the geology of the bluff upon 

 which the fort is erected correspond with those made at the 

 Falls of St. Anthony, with this exception, that, at the latter 

 place, our observations are limited to the three superior 

 strata, viz : the slaty limestone, with organic remains ; the 

 blue limestone, destitute of these ; and the sandstone, with a 

 loose texture. The falls are occasioned by the fissures which 

 occur in the superior limestone, and which allow the water to 



