CHAPTER IX. 



THE EARLY WISCONSIN DRIFT SHEETS. 



GENERAL STATEMENT. 



The northeastern fourth of Illinois and adjacent portions of Indiana are 

 covered by a sheet of drift somewhat fresher than the Iowan, which has its 

 terminus in the Shelbyville moraine, but which embraces several morainic 

 systems of considerable prominence that lie between the Shelbyville moraine 

 and the border of Lake Michigan. The term "early Wisconsin" is restricted 

 to the moraines which lie outside the bulky moraine that encircles the head 

 of the lake and which was discussed by Chamberlin in the Third Annual 

 Report as the terminal moraine of the second Glacial epoch. In that report 

 Chamberlin referred briefly to the occurrence of morainic lines outside the 

 moraine which formed the theme of his paper, and recognized the general 

 freshness of the drift and unsculptured contour of its surface compared 

 with that of the districts nearer the glacial boundary and outside the limits 

 of the Wisconsin drift. 1 The group here recognized as the early Wisconsin 

 forms a somewhat concentric series, as may be seen by reference to the 

 glacial map (PL VI). The moraines included in the late Wisconsin are not 

 concentric with the earlier group. On the contrary, they cross the earlier 

 moraines in western Indiana and override the greater portion of the district 

 which the early Wisconsin occupies. In Illinois the early Wisconsin is well 

 exposed outside the late Wisconsin series, probably better than in any 

 other part of the glaciated district. If our interpretations are correct, it is 

 only represented by a single moraine in eastern Indiana and southwestern 

 Ohio, while farther east it is entirely concealed by the later deposits or so 

 merged with them as to have escaped recognition. 



'Third Ann. Rept. U. S. Geol. Survey (for 1881-82), 1883, p. 331. 



