66 ILLINOIS STATE ACADEMY OP SCIENCE 



GENERAL HISTORY OF THE ICE INVASIONS 



For more than a score and a half of years it has been 

 known that the glacial period was a complex period of ice 

 invasions, rather than a single epoch ; that it included five 

 distinct glacial epochs separated by long periods of warm 

 climate, each intergiacial epoch being in most cases much 

 longer than the time since the last glacial epoch. 



Eecords of the earlier ice invasions, however, are not 

 to be seen in the Elgin region. Most of the earlier glacial 

 history has been worked out in Other parts of Illinois and 

 in adjoining states, rather than in this area. We feel 

 quite certain, however, that this territory was trans- 

 gressed by at least three different ice sheets, although 

 the full record is not visible here. Old soils separating 

 glacial tills have been penetrated by various wells in this 

 locality at depths ranging from about 40 to 137 feet. 

 These old soils are striking evidence of one or more of 

 the intergiacial epochs when the climate became so mild 

 that the ice sheet was melted away and soil making pro- 

 cesses were active. 



While it can not be claimed that the Elgin area is a 

 type locality of the older drift sheets, it does have the 

 distinction of showing in a way perhaps unsurpassed by 

 any other locality in this or any other state, the late 

 glacial history. 



MORAINAL BUILDING 



At the time of the invasion of the Wisconsin ice sheet, 

 the basins of the Great Lakes had outlines somewhat 

 similar to their present ones. The concentric arrange- 

 ment of the moraines about these basins shows that the 

 basins caused the ice to become organized into fairly dis- 

 tinct lobes with radial motion. In the case of the Lake 

 Michigan lobe, the general direction of ice movement was 

 southward, with radial motion towards the east and west 

 sides. In the Elgin locality, the direction of the ice 

 movement was to the southwest. The greatest extent of 

 this ice sheet was to Peoria and Shelbyville on the south- 

 west. With oscillatory changes in climate from cold to 

 warm, the ice front began its recession, but the oscillatory 

 nature of these climatic changes brought about halts or 



