EROSION AL HISTORY OF DRIFTLESS AREA 23 



ed strata during maturity, streams which have courses 

 parallel or oblique to the dip and flow the shortest distance 

 to the sea, afford good evidence that the region has suffered 

 more than one cvcle of erosion. 



Fiir. ?. Diajn-am illustratinir Stage HI of 

 stream adjustment. (After Davis). 



In case a region under investigation is not one of folded 

 structures, the same general methods as outlined above may 

 be applied. The stages of adjustment can be worked out 

 and the corresponding stage of reduction. If the stage of 

 reduction and stage of adjustment do not harmonize, the 

 stream courses furnish evidence of more than one cycle of 

 erosion. 



It must be recognized that by extremes in slope streams 

 might work headward through hard rocks and that b^* ex- 

 tremes in non-resistance, they might extend headward 

 through topographic elevations so as to flow through water- 

 gaps, all in the first cycle. It is not probable, however, that 

 anvthing but the smaller streams of a region would in this 



