EROSIOXAL HISTORY OF DRIFTLESS AREA 109 



the smallest, as illustrated in Fig. 34. This fact is of some 

 value as evidence in favor of the idea that more than one 

 cycle was involved in the erosional historv of the Driftless 



Fig. 34. A plat of part of the course of Grant river and its n-ib- 

 utai-ies. The fact that the tributaries are not nearly so crooked as 

 the main stream suggests that the curves of the river were developed 

 in the last stages of a previous cycle and that the tributaries were 

 mainly or ■nholly developed in the present cycle. 



Area. This evidence is chiefly corroborative, however, and 

 is not conclusive considered alone. 



Stream Terraces 



The Driftless Area abounds in stream terraces of vari- 

 ous sorts, but none of them is significant as an evidence of 

 more than one cycle of erosion. 



At many points throughout the area there are projections 

 or benches along the valley walls, whose tops are more or 

 less flat, whose outer faces are steep, and to which the term 

 terraces might be applied. These feature.? are well known 



