THE WEATHERED ZONE (SANGAMON) BETWEEN 

 THE IOWAN LOESS AND ILLINOIAN TILL SHEET. 



PRELIMINARY STATEMENT. 



Extent of Illinoian till sheet. — The Illinoian 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 Illinonian 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 northern 

 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 Kansas 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 recog- 

 nized farther west than the limits of the Illinois glacial lobe. It 

 seems probable, however, that it may be found in the 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 the gla- 

 cial boundary from St. Louis eastward as indicated above. It is 



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