110 S. CAf.VlN — lOWAN UUII'T 



The eastern or northeastern Ijoundary cuts the Iowa-Minnesota line near 

 tlie northwest corner of Winneshiek county. Its course from this point 

 is. in tlie main, southeast, cutting across the northeast corner of Fayette 

 and tlic southwest corner of Clayton. It clips off the northeastern corner 

 of Delaware county, is exceedingly sinuous in the western part of the 

 county of Dubuque, trends southward with many tortuous windings 

 through Jones, and finally sweeps eastward, six or eight miles south of 

 the north line of Clinton county, to the Mississippi river. The free edge 

 of the lowan ice, however, flowed out in numberless digit-like lobes, 

 some of which were surprisingly long and narrow, and so its boundary 

 lines along the terminal margins are irregular and sinuous to the last 

 degree. Except at one or two points, the eastern boundary of the lowan 

 falls short of the western edge of the Driftless area, the space between 

 the extreme limits of the lowan in this direction and the Driftless area 

 being occupied with typical weathered Kansan overlain by loess. 



Characteristics of the Iowan Drift 



topography 



The lowan drift presents a number of ver}^ constant, easily recognized, 

 specific characteristics. In the first place, the topography is very strik- 

 ing. The surface is a broad plain, marked by long, gentle, sweeping 

 undulations. The curves are low and flat, and the concave portions of 

 the profiles are in many cases longer than the convex. Erosion since 

 the retreat of the lowan ice has played no part in producing the main 

 topographic forms. The surface inequalities are irregularly disposed 

 and are due, for the most part, to the erratic heaping up of materials, in 

 some places more than in others, b}' the action of the lowan ice. The 

 main drainage courses are fiiirly well defined, many of them following 

 sags determined b}^ the jjresence of partly filled pre-Iowan valleys of 

 erosion. Along the larger streams incipient erosion forms occur, extend- 

 ing back as small lateral channels and intervening ridges for a fraction 

 of a mile or so ; but the development of such forms is always on a small 

 scale, and over the intervening spaces, which constitute by far the greater 

 part of the lowan area, the drainage is effected by flow of water along 

 the broad, shallow depressions of the surface, without following definitely 

 cut channels. Even in the case of the principal drainage courses the 

 amount of stream-cutting since the retreat of the lowan ice is insignifi- 

 cant. Tlie channels in the typical portion of the area are mere trouglis 

 or canals cut Init little below the level of the broadly undulating drift- 

 plain. The streams have no valleys, nor have they any floodplains, and 



