PAPERS OX BIOLOGY AND AGRICULTURE 



205 



the ice melted under the rain-dehiges of its own begetting, 

 back in the earliest post-pleistocene, and here one still 

 finds them : conifers and ericads and reindeer-lichens. It 

 was up the rich and sheltered valleys that the plants of 

 a milder climate came, pawpaws and tnlip-trees and* sas- 

 safras, and it is in the valleys that they have held their 

 place. Where the country rock is a sandstone, as at 

 Starved Eock, the newcomers from the southwest, cactus 

 and sagebrush and bunchgrass, gained and kept a foot- 

 hold where the soil from its decomposition accumulated. 

 And everj-^vhere one can find places where the whole suc- 

 cessional series proper to the region, from the burr oak 

 of the prairie edges and the black oak of the dry upland 

 woods, lie only a literal stone's throw from the elm and 

 linden of the floodplain and the willows at the water's 

 edge. 



An excellent illustration of such a place is Lovers' 

 Leap cliff at Starved Eock, shown in figure 2. (A Lov- 

 ers' Leap is another feature that most of these canyons 



JFig. 1. Map showing distribution of representative river canvon s. 



1. Sugar Creek region 5. The Dells of the Wisconsin 



2. Turkey Run 6- Wildcat Glen 



3. Starved Rock 7. Palisades of the Cedar 



4. Apple River 8. Steamboat Rock 



