ORIGIN OF NAME AND AREA OCCUPIED 109 



in a "monotonous simplicity of surface configuration "and in ponderous, 

 boulders projecting conspicuously above the surface. The assumption 

 however, that there were but two till sheets in the area considered, and 

 that they were sei3arated by an old soil and forest bed, was the cause of 

 assigning to the upper till in certain localities a number of characteristics 

 that do not belong to the superficial drift of Bremer, Black Hawk, and 

 Buchanan counties. Taking the latest glacial deposit of these counties as 

 the true upper till of McGee, we have a drift-sheet characterized by defi- 

 nite and consistent individuality and sharpl}^ delimited in its geogra]ihic 

 distribution. 



In the third edition of Geikie's " Great Ice Age " Chamberlin proposes 

 the name East lowan for the upper till of McGee.* The characteristics 

 of the formation are enumerated in detail, and are made broad enough 

 and variable enough to include all the Pleistocene deposits down to the 

 forest bed, which is so conspicuous a feature of the drift series not onl}^ 

 in Iowa but very generally throughout the Mississippi valley. Some- 

 what later,t following the suggestion of Mr Upham, Chamberlin abbre- 

 viated the term to lowan, and it is needless to say that the shorter name 

 was welcomed and has since been very generally adopted. Chamberlin's 

 latest classification of the glacial series of the Mississippi basin recognizes 

 the limitations assigned in this paper to the lowan drift. 



Area occupied by the Iowan Drift-sheet 



The lowan drift as at present recognized is superficial over an area in 

 northeastern Iowa and southeastern Minnesota east and southeast of 

 the Altamont moraine. In Iowa the moraine bounding the lowan area 

 on the west passes southward from near the middle of the north line of 

 Worth county. It includes Clear lake in one of its basin-like depres- 

 sions, and gradually fades out in Hardin and Marshall counties. This 

 moraine marks the eastern edge of the Wisconsin lobe and overlaps the 

 lowan from the Minnesota state line to near the southern boundary of 

 Hardin county. South of Hardin county the Wisconsin drift rests on a 

 till that is very much older than the lowan, on what has recently come 

 to be called the Kansan. 



The southern limit of the lowan till coincides in a general way with 

 the course of the Iowa river from near Albion, in Marshall county, to 

 the great elbow west of Solon, in Johnson county, from which point the 

 general trend is eastward to near the mouth of the Wapsipinieon river. 



* James Geikie : The Great Ice Age, third ed., p. 750. 



fThe Journal of Geology, vol. iii, pp. 27U and 273 ; vol. iv, p. 871. 



