EROSION AL HISTORY OF DRIFTLESS AREA 105 



and the problem of their antecedency is therefore obscured. 

 Upper Iowa river has a course N 46°E from Decorah to its 

 mouth, which fails of parallelism with the dip by 142°. In- 

 deed the river flows for 35 miles in a direction which must 

 have been up an original slope of 10 or 15 feet per mile. If 

 glaciation had nothing to do with the establishment of this 

 course Upper Iowa river is probably antecedent. Turkey 

 river below Elkader flows in the general direction S 66°E. 

 As this makes an angle of only 2° with the strike of the 

 strata, Turkey river may be considered to be adjusted in 

 harmony with its development within a single cycle. In 

 Minnesota, Root river has a course out of harmony with 

 the structure and the slopes of the theoretic original sur- 

 face. It flows in a general direction which is up a strati- 

 graphic dip of 4 feet per mile, although by taking a more 

 southerly course it could have flowed around the end of 

 the plunging anticline. Although Whitewater river north 

 of the axis of the arch, as stated on p. 102, flows in a 

 direction which is in harmony with structure and original 

 slope, it joins the Mississippi with an acute angle down- 

 stream, suggesting the possibility that its course was estab- 

 lished according to original slope and maintained after re- 

 versal of the master stream. Thus, while there is little 

 suggestion of antecedency for the Whitewater river itself, 

 its course taken in connection with the course of its main, 

 adds strength to the belief that the establishment of the 

 present course of the upper Mississippi involved a case of 

 piracy of a magnitude which could hardlj' have taken place 

 all within the present cycle of erosion. 



In Illinois, Sinsinawa Creek, Galena River, Smallpox 

 Creek, Apple River and Plum River are so nearly parallel 

 with the dip that their histories probably do not date back 

 of the present erosional cycle. 



Intrenched Meanders 



If the erosional history of the Driftless Area has involved 



more than one cycle of erosion it seems that some of the 



streams at least should have developed meanders in old ago 



of a cvcle and intrenched their meanders in the later cvcla 



