128 IOWA DEPARTMENT OF AGRICULTURE. 



the surface anywhere since the lowan glaciers retreated from the state. It 

 is true that, in places, the surface is more or less undulating and irregular, 

 but such inequalities as do exist were brought about by the erratic and dis- 

 orderly way in which the transported materials were distributed at the time 

 the ice disappeared. Prior to the general occupation of the region by the 

 white man, there were extensive undrained sloughs covering a large percent- 

 age of the entire area. The rivers of the lowan region illustrate in an ideal 

 way the characteristics of young streams. They have cut no valleys; they 

 simply flow in narrow, shallow trenches at the level of the drift plain. 

 The minor drainage courses are very largely broad sags in which there 

 is not, as yet, even the beginning of a definite stream channel. Cultivation 

 and artificial drainage have wrought greater changes in the surface, in the 

 last score or two of years, than had been accomplished in all the preceding 

 centuries since the lowan stage came to a close. Large granite bowlders 

 ranging up to thirty, forty, or even fifty feet in diameter, are characteristic 

 features of the lowan area. The outer margin of the lowan plain is usually 

 quite sharply defined by a thickened ridge of the fine silt-like clay called 

 loess. (PI. I, Fig. 2.) From the summit of such a marginal ridge the 

 observer looks outward upon the billowy and deeply eroded surface of the 

 older Kansan (PI. I, Fig. 1); in the other direction the young, uneroded 

 lowan plain extends away to the horizon, as level as the surface of the sea. 

 (PI. I, Fig. 3.) 



Younger than the lowan is the Wisconsin drift, which, so far as our own 

 state is concerned, covers an area nearly triangular in shape. The base 

 of the triangle, where the comparatively narrow ice lobe crossed from Min- 

 nesota to Iowa, extends from Worth county to Osceola; the apex is at Des 

 Moines. Through the western part of Worth, Cerro Gordo, Franklin and 

 Hardin counties the edge of the Wisconsin drift overlaps the lowan; the 

 apex of the Wisconsin lobe rests at Des Moines on the older Kansan. The 

 Wisconsin area is in general a level ill-drained plain. The traveler may go 

 for scores of miles without seeing a definite drainage trench so much as a 

 foot in width or depth. Saucer-shaped depressions or "kettle holes,' 

 varying from a rod or two, to an eighth or a quarter of a mile in diameter 

 are common features of the Wisconsin plain. 



The Wisconsin, more than any of its predecessors, was a moraine form 

 ing ice sheet. Part of the transported materials was piled up around the 

 margin of the lobe in a bewildering series of disorderly hills or knobs, vary 

 ing from eighty to one hundred and fiftyl feet in height. A well char 

 acterized belt of lawlessly heaped up morainic knobs six to ten miles 

 wide, extends from the north line of Worth county to the south line of Cerro 

 Gordo, from which point southward the knobby character of the Wisconsin 

 margin becomes less pronounced. Pilot Knob, near the northeastern corner 

 of Hancock, is the most noted and the most prominent of these great 

 morainic heaps of drift. The marginal moraine is well developed at many 

 points along the western edge of the Wisconsin lobe. It forms a belt of 

 more or less prominent hillocks and knobs passmg through Osceola, Clay, 

 Buena Vista, Sac and Carroll counties. As on the eastern margin, the 

 morainic characters gradually fade out toward the south. While the Wis- 

 consin ice lobe was slowly melting and disappearing from the state, the 

 retreating margin halted at intervals for periods long enough to pile up con- 



