EROSIONAL HISTORY OF DRIFTLESS AREA 97 



of sloi38, resistance, and structure and with the stage of early 

 maturity, or they are antecedent and have courses now 

 which they acquired in some late stage of a previous cycle. 

 If the streams are merely consequent it would seem that the 

 surface of the Driftless Area is in its first erosional cycle. 

 If they are antecedent they furnish valuable evidences of 

 more than one cycle in the erosional history of the region. 

 In case there has been but one cycle of erosion all the 

 streams should be consequent ; if there has been more than 

 one cycle the larger streams are likely to be antecedent. 

 having developed their courses in the first cycle and held 

 them into the second, and the many tributary streams 

 should have been developed in the present cycle and be con- 

 sequent. The problem then involves especially the major 

 streams. 



Mississippi River 



Study of the present course of the Mississippi river shows 

 certain anomolies in its relations to original topography and 

 structure, which are significant. These anomolies can be 

 made most clear by a study of the various stages of adjust- 

 ment which major streams should have in the normal ero- 

 sional cycle under conditions existing in the Driftless Area, 

 and by comparison of the course of the Mississippi river 

 with these various stages, considering the present mature 

 condition of the region. 



As has been stated in previous pages, the strata south 

 from La Crosse and Sparta dip in an average direction 

 S 26°W to an average amount of 14.6 feet to the mile. But 

 north of Winona along the Mississippi a dip in the opposite 

 direction is recorded by conformable stratigraphic contacts 

 which decline appreciably from Winona to Minneapolis. 

 The average dip of the strata north of the arch, which 

 seems to run through Galesburgh, Winona, and St. Charles, 

 determined by taking the averages of four computations by 

 means of the three point method is found to be N 35° 

 W 9.3 feet per mile. The highest portion of the 

 original surface, therefore, must have been near Winona 

 and the surface must have sloped down to the north and 



