ABSTRACT OF VOLUME. 



Chapter I. Introduction.— The Illinois glacial lobe formed the southwestern 

 part of the great ice field that extended from the high lands east and south of Hudson 

 Bay southwestward over the basins of the Great Lakes and the north-central States 

 as far as the Mississippi Valley. It overlapped a previously glaciated region on the 

 southwest, whose drift was derived from an ice field that moved southward from the 

 central portion of the Dominion of Canada as far as the vicinity of the Missouri River. 

 This southwestern part of the eastern ice field, being mainly within the limits of the 

 State of Illinois, has received the name Illinois Glacial Lobe. 



The results of earlier studies by Chamberlin, Salisbury, and others are noted, 

 and the plan of investigation is set forth. A brief explanation of the method of num- 

 bering townships is i)resented. 



Chapter II. Physical features. — The variations in altitude are set forth in 

 a topographic map and also in tables, and the marked increase in altitude of certain 

 parts of the region because of drift accumulations is considered. The conspicuous 

 reliefs of the rock surface are briefly touched upon, and the preglacial valleys receive 

 passing notice. Profiles and maps are extended across the bed of Lake Michigan as 

 well as border districts, and the inequalities of the lake basin are briefly discussed. 



Chapter HI. Outline of time relations or glacial succession.— A 

 sketch of the major and minor divisions of the drift sheets and of the intervals 

 between them is accompanied by a brief explanation of the basis for the classification 

 adopted. 



Chapter IV. The Illinoian drift sheet and its relations. — The Illinoian 

 is tlie most extensive drift sheet formed by the Illinois glacial lobe and receives its 

 name because of its wide exj:>osure in the State of Illinois. The evidence that the 

 Illinoian drift sheet should be separated from the outlying and underlying drift and 

 also from the Iowan drift is briefly set forth. The aspects of the Illinoian drift sheet 

 are then discussed, its topography as well as its structure being considered. In 

 connection with this drift sheet a very adhesive clay, known as "gumbo," which 

 caps it, is described and the questions of its relation to this drift sheet and to the 

 overlying loess are considered. A detailed description of the border of the Illinoian 

 MON XXX.VIII 2 XVii 



