PAPERS PRESENTED AT GENERAL SESSIONS 65 



THE GLACIAL HISTORY OF THE ELGIN REGION 



M. M. Leighton, Chief Illinois Geological Survey 



The City of Elgin is situated in one' of the most inter- 

 esting- glaciated localities of the country. The surround- 

 ing- landscape portrays in remarkable fashion the archi- 

 tectural work of the great ice sheet. A great deal of study 

 has been given the glacial history of this portion of the 

 State by various workers, including Professors Chain- 

 berlin, Leverett, Trowbridge, MacClintoek, Goldthwait 

 and others, but there are still details to be deciphered. 

 Notwithstanding the fact that the full history is not 

 known, it nevertheless may be of interest to recite the 

 facts as we now have them in hand, subject of course to 

 the results of future study. 



pee-glacial history 



Before the glacial period, this general area had a 

 markedly different aspect from its present. Before the 

 incursion of the first ice sheet, this was a territory of 

 limestone hills and valleys, mantled with such soil and 

 lual clays as result from the weathering .of the Ni- 

 agaran dolomite. The present valleys, with their erratic 

 tributary development, were not here, but instead a sys- 

 tem of valley development of the leaf -like or dendritic 

 form similar to that of the driftless area of northwestern 

 Illinois, although there was' less relief. The jt resent 

 topography has come about from a heavy mantling of 

 this old erosional landscape with glacial drift deposited 

 in a series of recessional moraines with intervening 

 belts of ground moraine. The uplands at the present 

 time have an altitude of 900 to 1000 feet above sea level. 

 From the records which we have of well drilling, the 

 bedrock has an altitude of approximately (350 to 700 feet. 

 In other words, if the old bedrock topography were to be 

 restored, a glacial drift which ranges in thickness from 

 100 to approximately 300 feet would have to be removed. 

 Clearly, the deposition of the glacial drift in the Elgin 

 area has revolutionized the old topography, giving the 

 country a markedly different aspect from what it had 

 previously. 



