GEOLOGICAL AND NATURAL HISTORY SURVEY. 1 I 



OUTLINE OF TIME RELATIONS OR GLACIAL SUC- 

 CESSION. 



The complexity of the glacial events is such that it will be 

 advantageous to outline as clearly as possible at the outset the 

 recognized glacial succession and thus learn the position of the 

 drift of the Chicago Area in the series of drift sheets displayed 

 in the Mississippi Basin and adjacent territory. The outline given 

 below aims to present simply the recognized subdivisions. These 

 may prove to dififer widely in rank or importance. The main divi- 

 sions here outlined seem to be much longer than the secondary 

 divisions and they may be of very unequal length. They appear 

 to have the rank of an epoch, or main division of a period, except 

 the divisions of Lake ^history, which, perlhaps, should be substages. 

 The outline aims to cover the events between the deposition of the 

 oldest recognized drift sheet and the final recession of the ice 

 sheet into the region north of the Great Lakes. That region may 

 furnish several additional substages and possibly one or more 

 stages. The outline differs from that published by Prof. T. C. 

 Chamberlin, in a recent number of the Journal of Geology (i), 

 only in being a fuller presentation of substages in the Wisconsin 

 drift series, and in including the lake history of this region. 



OUTLINE OF THE DRIFT SHEETS AND INTEKVALS. 



1. Oldest recognized drift sheet- — ^the Albertan of Dawson. 



2. First, or Aftonian, interval of recession or deglaciation. 



3. Kansan drift sheet of the Iowa geologists. 



4. Second interval of recession or deglaciation. 



5. lUinoian drift slheet. 



6. Third, or preloessial, interval of recession or deglaciation. 



7. lowan drift sheet and main loess deposit. 



8. Fourth, or postloessial, interval of recession or deglacia- 

 tion. 



9. Early Wisconsin drift sheets. 



Substage i. Shelbyville morainic systein. 

 Substage 2. Champaign morainic system. 

 Substage 3. Bloomington morainic system. 

 Substage 4. Marseilles morainic system. 



10. Fifth interval of recession, shown by shifting of ice lobes. 



(1) Journal of Geology, Chicago University. Vol. IV, No. 7 Oetober-November. 

 896, pp. 8?2-876. 



