THE lOWAN-WISCONSIN BORDER 



E. J. CABLE 



Workers of the Pleistocene of Iowa must use several criteria for 

 distinguishing the different drift sheets. The working criteria are, 

 (1) surface topography of the drift, (2) distinctive lithological 

 characteristics, (3) degree and depth of leaching and oxidation, (4) 

 distinctive interglacial deposits and, (5) pronounced erosional and 

 weathered zones. It was formerly thought to be quite an easy 

 matter to distinguish one drift sheet from another by means of 

 criteria (1), (2) and (3), with great emphasis upon (1) and (3). 

 Too much emphasis, however, cannot be placed upon the lithological 

 characters, since a careful study of the drift sheets, with the pos- 

 sible exception of the Wisconsin, has revealed a certain consan- 

 guinity existing among them. 



The general composition of the drift being indistinctive where 

 two or more drift sheets are contiguous or are overlapping, it is 

 necessary to apply all of the above criteria where possible to dis- 

 cover them. 



In attempting to determine the boundary of the lowan-Wiscon- 

 sin drift sheets, all of the above evidences should be carefully ap- 

 plied where possible. 



The lowan-Wisconsin border has been located largely upon the 

 basis of topographic evidence. This has been due, no doubt, to, (1) 

 lack of sufficiently deep cuts where the relation of one drift to 

 another may be seen, and, (2) the greater emphasis that was earlier 

 placed upon lithological characters and surface topography. 



After having spent some time in studying carefully the lowan- 

 Wisconsin drift border from where it enters Iowa in northwestern 

 Worth county to northern Hardin county, the writer feels confident 

 that there are many places where changes in the position of the 

 border should be made. Detailed investigation was made to deter- 

 mine, first, if possible, whether the lowan drift extended westward 

 beneath the Wisconsin drift. Many difficulties are encountered 

 when an attempt is made to secure data to determine the relation of 

 the lowan drift to the Wisconsin drift, as, (1) the great thickness 

 of the Wisconsin drift at its eastern margin, (2) the absence of 



