EROSION AL HISTORY OF DRIFTLESS AREA 91 



of slope of the plain is S 40 'E and the average amount of 

 slope 3 feet per mile, while the corresponding figures for 

 the strata are S 12'\V and 11.3 feet. Including the results 

 of all the estimates, both local and general, the plain slopes 

 S ll'E to an amount of 7.6 feet to the mile and the strata 

 dip S. 20 \V. 14,4 feet per mile. The plain and the strata 

 fail of parallelism by 31' in direction and 6.8 feet per mile 

 in dip. 



In the literature of the subject the Lancaster plain and 

 the Dodgeville plain have in some cases been confused : in- 

 deed there has been some doubt expressed that they are 

 really distinct. In his criticisms of the peneplain theory to 

 explain the accordant divides of the Driftless Area, Mar- 

 tin^ assumes two cases: (1) that there are four upland 

 plains, one for each cuesta, and (2) that there is but one 

 upland plain. He does not consider the problem of two up- 

 land plains and appears to believe that all the upland sur- 

 faces form a single plain, if indeed they may be said to 

 form plains at all. This confusion doubtless grows out of 

 the fact that there are places where the summit plain only 

 is found and places where only the intermediate plain oc- 

 curs. In such latter places the Lancaster plain could easily 

 be mistaken for a summit plain. There are also some local- 

 ities within the Driftless Area in which both plains occur 

 and where they appear to grade into each other. 



And yet the summit plain and the intermediate plains 

 are distinct. The evidences are as follows: (1) In most 

 portions of the Driftless Area, as between Waukon and the 

 Mississippi river (Fig. 23), and in the district south of 

 Turkey river in Iowa, in the Galena and Elizabeth quad- 

 rangles in Illinois, in the northern and central portions of 

 the Lancaster and Mineral Point quadrangles, in the Rich- 

 land Center quadrangle, in the Baraboo district and in the 

 Sparta quadrangle in Wisconsin, and in ^Minnesota both 

 plains are found and in most of these places the lower 

 plain is so sharply set off from the upper one that the two 

 can be distinctly seen in any general view, (2) Even in 

 districts where intermediate levels seem to grade into sum- 



1, Martin, Lavrrence, Bull. No. 36. Wis. Gcol. and Xat'l Hist. Surv., pp. 66-67. 



