IOWA ACADEMY OF SCIENCES. 71 



THE WEATHERED ZONE (SANGAMON) BETWEEN THE 

 lOWAN LOESS AND ILLINOIAN TILL SHEET. 



BY FRANK LEVERETT, DENMARK, IOWA. 



PRELIMINARY STATEMENT. 



Extent of Illinoian Till Sheet. — The lUinoian till sheet here 

 discussed was formed by the Illinois glacial lobe in connection 

 with the maximum extension of that lobe. It seems quite well 

 established that a lobe on the east, which covered southeastern 

 Indiana and southwestern Ohio, and extended a short distance 

 into Kentucky, also had its culmination at the Illinoian stage 

 of glaciation. Farther east the Wisconsin sheet in many places 

 reaches the glacial boundary, but there are small tracts of drift 

 older than the Wisconsin, lying outside its limits in eastern 

 Ohio, northwestern and northeastern Pennsylvania, and north- 

 ern New Jersey, which may prove to be of Illinoian age, 

 though this is as yet, not established. 



To the west of the Illinois glacial lobe there is a large area 

 covering northern Missouri, southern Iowa, northeastern Kan- 

 sas and eastern Nebraska, in which the upper sheet of till is 

 older than the ■Illinoian, and is now referred to the Kansan 

 stage of glaciation. The lobe which formed it is here referred 

 to as the western lobe for it has as yet received no more definite 

 name. The Illinoian sheet has not been recognized farther 

 west than the limits of the Illinois glacial lobe. It seems 

 probable, however, that it may be found in this western region, 

 and possibly it occurs as far south as northern Iowa. 



The Illinois glacial lobe at its maximum extension to the 

 southwest, crossed the Mississippi and encroached a few miles 

 on Iowa, in the district between Clinton and Ft. Madison. But 

 farther north and south it appears to have terminated east of 

 the Mississippi, except perhaps, for a few miles near St Louis, 

 Mo. The southern border of this lobe apparently reached to 



