EROSION AL HISTORY OF DRIFTLESS AREA 69 



Niagara dolomite was deposited in this sea over the whole 

 region, and the plain is directly underlain by Huronian 

 rocks at Baraboo, the Prairie du Chien formation at Sparta, 

 the Galena formation at Church and Waukon and on Mili- 

 tary Ridge. From these portions of the surface younger 

 rocks must have been eroded. Also there are monadnocks 

 standing above the level of this surface at several places, 

 for instance, Sauk Point in the Baraboo district. Blue 

 Mounds at the east end of Military Ridge, and Sherrill and 

 Sinsinawa Mounds farther south. 



Neither is the Dodgeville plain the result of marine de- 

 nudation. The erosion remnants above it are not isle-like, 

 nor is it bordered anywhere by shore features, A still more 

 significant fact is that marine deposits, younger than the 

 rock formations across the edges of which the plain is de- 

 veloped, are wholly wanting on the summit surfaces of the 

 region, although other deposits have been preserved there. 

 It is also extremely doubtful if such broad wave-cut terraces 

 have ever been developed anywhere, especially far in the 

 interiors of continents. 



The theory that the Dodgeville plain was formed on the 

 surface of a single especially hard formation is untenable 

 for the reasons that the plain lies on different formations 

 at different places, that not all the formations are resist- 

 ant, and that the plain slopes southward at a considerably 

 lower angle than the angle of dip of the rock formations. 



The idea that the Dodgeville plain consists of a series of 

 unrelated structural plains is incoroprated in the theory 

 that the plain is a series of cuesta tops, and this theory is 

 next to be considered. 



The Cuesta-Single Cycle Theory 

 Of the first four possible interpretations outlined above, 

 the idea which has been advanced that the Dodgeville plain, 

 as described on previous pages, does not exist and never did 

 exist, but consists merely of a series of unrelated cuestas, 

 is more probable than any of those thus far considered, and 

 is to bo accepted or rejected only after the most careful 

 study of the field conditions. A possible source of confusion 



