STUDIES IN THE DRIFTLESS REGION OF WISCONSIN 1 9 1 



notes. The minor features of distribution also harmonize well 

 with it ; for example, in Fig. 6, limestone is wanting on the 

 north side of the buttress. But this side is remarkably high and 

 the height is maintained for a long distance, and the upper sur- 

 face of a drift having the average slope would have fallen much 

 below the top of the perpendicular escarpment. Conversely 

 there are other buttresses so small that a drift having the aver- 

 age slope would have buried them completely, and these also 

 are destitute of the limestone. 



It is evident that on this hypothesis the limestone accumula- 

 tions furnish data from which we may calculate approximately 

 some of the dimensions of the drifts. In some of the circs the 

 slope may have been as high as 20° in places, but the average 

 appears to have been nearer 15 . In the valleys it was much 

 less, apparently ranging from io° or 12° down to 4 or 5 . The 

 greatest vertical thickness appears to have ranged between 200 

 and 250 feet in the valleys and between 80 and 120 feet in the 

 circs 



The hypothesis does not necessarily imply that the big drifts 

 developed glacial motion, since the transit across their upper 

 surfaces might have taken place though the drifts were them- 

 selves stationary. But if we may accept the existence of large 

 bodies of snow in the valleys, as probable, the indices of glaci- 

 ation shown in the lower portions of the same valleys gain 

 greatly in importance. 



The facts above given regarding the distribution of limestone 

 on the bounding buttresses of circs, seems to render it desir- 

 able that some notice should be taken of their low level depos- 

 its. Unlike those connected with the larger valleys, these are 

 almost whollv external, and have the form of alluvial cones. 

 As seen in section, they display the concentric structure lines 

 indicating the successive stages of their upbuilding. These are 

 more pronounced on either side of the center where also the 

 material is usually fine. 



Along the center, or axis, bedding planes are often faint, or 

 lacking, and much heavy material is included. As might be 



