194 ILLINOIS STATE ACADEMY OF SCIENCE 



POT-HOLES AND CERTAIN FEATURES OF 

 GLACIAL ABRASION 



Terrence T. Quirke, University of Illinois 



Illinois and neighboring states are covered to a con- 

 siderable extent by glacial deposits. These are subject 

 to local examination and study. Investigation of the 

 content of the drift shows that it is very largely of local 

 origin, but that it contains a noticeable amount of ma- 

 terial which has been brought from far beyond the local 

 outcropping rocks. Some of the material has been 

 brought from the northern side of the Great Lakes. In 

 the areas of southern Canada one may see the glacial 

 gathering grounds, stripped of their mantle rocks, ex- 

 posed today almost in the condition in which they were 

 left by the last ice sheet. 



This paper has to do with certain phenomena observed 

 in the Killarney area, a district on the north shore of 

 Georgian Ba} 7 , the extreme northeastern corner of Lake 

 Huron. This area is remarkable for the striking physi- 

 ographic contrasts it displays. Early in the history of 

 geological work in North America, the area was de- 

 scribed briefly by Alexander Murray 1 in 1848. No one 

 could pass this spot without seeing the great snow white 

 quartzite hills, known as LaCloche mountains, rising 

 above the hummocky granite plain which stretches with 

 little interruption to the Laurentian highlands of eastern 

 Ontario and Quebec. Here is a strange physiographic 

 disconformity, the sudden end of a great range of quartz- 

 ite hills, cut off transverse to their general line of extent 

 by a lowland of granite. In general, we find the tower- 

 ing peaks of folded mountains to be of igneous composi- 

 tion, but in this case, we find the plains are granite and 

 the hills sedimentary rocks. Examination shows that 

 the quartzite formations are faulted, and destroyed by 

 granite intrusions. 2 



ICE work 



The major effects of glaciation which are common to 

 most of the country north of Lake Huron are well illus- 



1 Alexander Murray, Exploration geologique du Canada, 1848, p. 113. 

 2 R. Bell, Geol. Surv. Canada Ann. Report, Vol. IX, 1898, pp. 8-9. A. 

 E. Barlow, Geol. Soc. Am. Vol. IV, 1893, p. 315-321. 



