EROSION AL HISTORY OF DRIFTLESS AREA 101 



Fig. 31. Blcck diagiam showing the ccurses of the streams 

 stream sdjustrr.ent in a first cycle of ercsicn. 



in a final stage of 



Now the present course of the ^Mississippi river in early 

 maturity of the present cycle of valley development is al- 

 most exactly what would be expected if it were determined 

 by two streams flowing in opposite directions from the 

 crest of the arch, the south-flowing stream having captured 

 the north-flowing one, as outlined above (Fig. 32). North 



Fig. 32. Blcck diagram showing roughly the course of the Mississippi river in its 

 relations to structure. The river is antecedent in the same sense that the Susque- 

 hanna river in the Appalachians is antecedent. 



of the axis of the arch, between Minneapolis and La Crosse, 

 the river flows in the general direction, S 51 'E, which is an 

 angle of 164' with the average direction of dip of the strata. 

 The river not only does not flow in the direction of the dip 

 but it does not flow parallel with the strike. Its average 

 direction lacks but 16' of being opposite to the dip and to 



