EROSION AL HISTORY OF DRIFTLESS AREA 71 



features can be explained as well on the basis of more than 

 one cycle as on the basis of a single cycle. There are also 

 several points now to be brought out by a more careful 

 study of topography, especially in its relations with struc- 

 ture, which cannot be explained on the cuesta-single cycle 

 theory and are in keeping with the multiple cycle theory. 



(1) The south slopes of the upland surfaces are not 

 parallel with the strata as is normal for cuestas. Compare 

 figures 1 and 4. The south slopes of the Dodgeville plain 

 correspond with the dip of the strata neither in direction 

 nor in amount, as shown in the preceding table (p. ) . 



(2) Those portions of the Dodgeville plain which lie 

 on a single rock formation bevel the layers of that forma- 

 tion. Within the bounds of the Sparta quadrangle, the 

 summit of the Prairie du Chien cuesta lies on 35 feet of 

 Prairie du Chien dolomite at Castle Rock, and on constant- 

 ly increasing thicknesses to the south, until 229 feet of the 

 form.ation appear below the cuesta top in the southwest 

 corner of the quadrangle. In the Galena and Elizabeth 

 quadrangles in Illinois the surface of the Niagara cuesta 

 cuts from a stratigraphic position 60 feet above the base 

 of the Niagara formation at the north border of the quad- 

 rangles to a position 170 feet above the base at the south 

 edge. Likewise the summit of the Galena-Platteville cuesta 

 lies 80 feet above the base of the Platteville limestone near 

 its northern edge in the Richland Center quadrangle and 

 300 feet above this horizon on one of the south spurs of 

 Military Ridge. This bevelling of different beds in forma- 

 tions by individual cuesta tops is also illustrated between 

 Church and Rossville, and between Updegraff and Monona 

 in Iowa, and at many other localities within the Driftless 

 Area. 



(3) In some places at least, two belts of cuesta tops 

 which are I'oughly parallel with the strike of the strata, are 

 connected by long, continuous, more or less broad summit 

 divides which are roughly parallel with the dip. Such a 

 divide is that connecting the Prairie du Chien cuesta in the 

 south portion of the Sparta quadrangle with the Galena 



