2 2 ERA NK LE VERE TT 



channel across the lower rapids would furnish a valuable chro- 

 nometer for determining the time since the Kansan stage of gla- 

 ciation. But from what has been shown, it is evident that the 

 determination of the time is at present very difficult, if not 

 impracticable. It may be thought that this channel will furnish 

 a chronometer for the relative dates of the Kansan, Illinoian, 

 Iowan, and Wisconsin glaciations. But on this question scarcely 

 more than a very rude approximation is likely to be reached. 

 As indicated above, the work involved in filling is very difficult 

 to determine. These difficulties, however, are no greater than 

 those involved in the estimates of the changes of drainage area 

 which the Mississippi has experienced. The object of the pres- 

 ent paper is accomplished if the complexity of the history has 

 been adequately presented. The chronological determinations 

 must be deferred to a time when more refined methods of inves- 

 tigation are instituted than are now at command. 



Frank Leverett. 



