EROSIONAL HISTORY OF DPJFTLESS AREA 117 



plain, and the graded plain of the Mississippi river, south 

 of La Crosse, are shown in the accompanying table, 



TABLE SHOWING THE RELATIVE DIRECTIONS AND AMOUNTS OF SLOPE OF 



THE DODGEVILLE PLAIN, THE LANCASTER PLAIN, AND 



THE MISSISSIPPI FLOOD PLAIN 



Plain Average direction of slope Average amount of slope 



Dodgeville Plain S 23'E 3.3 feet per mile 



Lancaster Plain S40"E 3 feet per mile 



Mississippi Flood Plain S18'E 4 inches per mile 



The difference in direction of slope of the Dodgeville and 

 Lancaster surfaces is not great, considering the possibilities 

 of error in estimating averages, and could be due to differ- 

 ences in direction of drainage during the respective cycles. 

 Consequently, they cannot be said to record warping or 

 lilting of the Dodgeville surface during uplift. The amounts 

 of slope of the Dodgeville and Lancaster plains are almost 

 identical, which seems to prove that there was no notable 

 tilting of the Dodgeville surface before the formation of 

 the Lancaster plain. The second diastrophic movement 

 recorded in the features of the surface was then one of 

 nearly uniform uplift. 



The amount of this uplift can be ascertained at least 

 roughly by the average difference in altitude between the 

 Dodgeville plain and the Lancaster plain. On the average 

 these two plains are 235 feet apart vertically in the Bara- 

 boo district, 265 feet in the Sparta quadrangle. 148 feet in 

 the Richland Center quadrangle, 175 feet in the Lancaster 

 and Mineral Point quadrangles, 218 feet in Jo Daviess 

 County, Illinois, 117 feet in the Waukon quadrangle, 190 

 feet in the Elkader quadrangle. 125 feet in southeastern 

 ^Minnesota. As the average of these figures is 184 feet, the 

 second recorded diastrophic movement was an uplift of 

 about that amount. 



The Lancaster cycle was interrupted by a third uplift 

 which was the greatest of all the movements which affected 

 the Driftless Area. Streams which had developed graded 

 flats on the Lancaster plain during the Lancaster cycle were 

 able in the following cycle to cut to the levels of the bottoms 

 of the rock valleys below the later fluvio-glacial fills. The 



