EROSIOXAL HISTORY OF DRIFTLESS AREA 79 



which have undoubtedly been deposited there by streams 

 which could not carry their loads all the way to the sea. 

 These deposits are known near Devil's Lake, Cashton and 

 Seneca in Wisconsin, and near Church, Elon and Waukon 

 in Iowa, as well as at numerous other places within and 

 south of the Driftless Area. This fact is not mentioned 

 by Martin. It seems to the writer to be a fatal objection 

 to the single cycle theory. 



The conclusion now has been reached that the Dodgeville 

 plain is not an original plain of marine deposition, nor a 

 plain of marine erosion, nor a simple structural plain. The 

 theory that the plain consists merely of three cuestas whose 

 summits were developed in the present cycle of erosion is 

 untenable. 



The Peneplain Theoi'y 



It remains to test the fifth possible interpretation. Some 

 of the points in favor of the theory that the plain is an 

 ancient peneplain dissected by erosion in subsequent cycles 

 have been touched upon indirectly in the analysis of the 

 cuesta theory. However, for the sake of definiteness and 

 completeness they are listed below. 



(1) The plain includes many upland surfaces so large 

 and so nearly flat that some effective agent of transporta- 

 tion, such as streams, must have operated there in order to 

 remove the large amount of material which originally ex- 

 isted at higher levels. (2) The plain has a slope of about 

 S to 5 feet per mile in a general southeasterly direction. 

 Its slope is notably different both in direction and amount 

 from the dip of the strata. (3) The general southerh' slope 

 of the plain is obscured locally by irregularities such as old 

 erosional surfaces show. Even locally the slopes of the 

 plain are not parallel with rock structures. (4) The plain 

 bevels the edges of rock formations irrespective of their 

 hardness. (5) In the formation of the plain, thicknesses 

 of rock have been removed, which decrease regularly from 

 north to south, bearing evidence that some sort of a grade 

 was established where the tops of the cuestas now are. 

 (6) The existence of certain continuous north-south ridges 



