PAPERS OX BIOLOGY AND AGRICULTURE 203 



I do not need to remind this audience that the dominat- 

 ing event in the history of all the botany of this region, 

 whether floristic or ecological, was the advent of the 

 glaciers. Their advance and retreat, and the postulated 

 climatic fliictnatious that have occurred since their final 

 disappearance, were the ultimate causes of the distribu- 

 tional peculiarities of floral disjuncts of northern, Appa- 

 lachian and southwestern affinities, as well as of the suc- 

 cessional relationships of the vegetational communities 

 proper to the region. The glaciers set the problems in 

 this part of the country for students of ecology and field 

 botany in general. 



Communities of floral disjuncts, as well as the most 

 clean-cut display of successional series, will always be 

 found where the greatest development of topographical 

 and soil diversities give rise to the most marked modi- 

 fications in ecological factors. These critical points, 

 these points of profitable attack, therefore, must be 

 sought out and studied not as discrete and unrelated 

 matters of interest, but rather as coordinated parts of a 

 whole. The rocky peninsulas and islands of the Super- 

 ior region, the morainal lakes of Minnesota and Wiscon- 

 sin, the dunes of Lake Michigan, and that remarkable 

 series of steep-sided river c<inyons scattered across the 

 upper Mississippi valley from Ohio to the Dakotas, are 

 all chapters in one great work, and all must be read be- 

 fore any may be fully understood. 



It is about the river canyons that I want to speak for 

 a few miimtes. In advance I want to say that I do not 

 come to tell about them, for I have only begun to try to 

 find out a little about a single one of them ; rather I stand 

 as one just a bit aghast at the size of the task and look 

 about for help. It is emphatically more than a one-man 

 job. What I bring is a challenge and an invitation. 



These canyons, as I have said, are scattered across 

 nearly the whole of the upper Mississippi valley. Many 

 of them have more than local repute. Sugar Grove in 

 Ohio, Turkey Eun in Indiana, Starved Eock and Apple 

 Eiver in Illinois, the Dells in Wisconsin, Wildcat Glen, 

 the Palisades of the Cedar and Steamboat Eock in Iowa, 

 are familiar enough names to most of us, and there are 



