124 IOWA DEPARTMENT OF AGRICULTURE. 



Another of the larger topographic features is the great watershed . This 

 is the ill defined ridge which extends in a sinuous course from Dickinson 

 county to Wayne and forms the line of parting between the waters flowing 

 to the Mississippi on the one side and to the Missouri on the other. The 

 watershed is in reality the southward extension of the noted ridge of the 

 Dakotas and southwestern Minnesota, known as the Coteau des Prairies. 

 An area somewhat greater than two-thirds of the state lies east of the water- 

 shed; less than one-third lies on the west. 



In the eastern area there is a comparatively short but rather important 

 ridge which is followed for some distance by the railway passing through 

 Calmar, Ridgeway, Cresco and Bonair. At Bonair the altitude is more than 

 1,300 feet. On one side the general slope is toward the Upper Iowa and the 

 Mississippi; on the other side the surface inclines stron8:ly toward the south- 

 west, the inclination being continued as far as the Cedar river. The stream 

 last named occupies the bottom of a broad trough which has the Cresco- 

 Calmar ridge for one margin, while Wesley in Kossuth county is situated on 

 the divide which forms the western rim. The eastern side of the trough 

 presents the interesting anomaly of a region drained by streams which flow 

 at an angle of but little less than 90° with the general inclination of the sur- 

 face'. For example, the direction followed by Crane creek and the numerous 

 branches of the Wapsipinicon is toward the southeast, but there is a much 

 greater fall to the mile toward the southwest. The southwesterly slope of 

 the surface is indicated by the following series of altitudes taken along a line 

 nearly at right angles to the present drainage: Arlington, 1,113; Oelwein, 

 1,049; Fairbank, 1,000; Dunkerton, 945; Dewar, 889; Waterloo, 841/ In 

 this direction, across the drainage courses, the average fall is more than 

 seven feet to the mile. Betw£en Oelwein and Waterloo the fall per mile is 

 exactly eight feet. In the direction of the drainage the average slope of the 

 surface is less than four feet to the mile. That the Cedar river flows in the 

 axis of a great trough is farther illustrated by such a series of altitudes as the 

 following, taken along the line of the Chicago, Milwaukee & St. Paul rail- 

 way: Calmar, 1,263; New Hampton, 1,169, Charles City, at the bottom of 

 the trough, 1.014; Nora Springs, 1,070; Mason City, 1,132; Garner, 1,223; 

 Britt, 1,235; Wesley, 1,258. Clear Lake is omitted from this last series for 

 the reason that it is located in the morainic ridge of the Wisconsin drift and 

 so stands above the general level of the surface sloping toward the Cedar 

 river . 



Minor and More Localized Features. — On the basis of the efiFects pro- 

 duced by the great ice .sheets of the glacial epoch, the surface of Iowa may 

 be divided into two parts, to be known respectively as the Driftless Area and 

 the Drift-covered Area. So far as size is concerned the driftless area is 

 quite unimportant, for it covers only the small fraction of the state embraced 

 in Allamakee county, and parts of Winneshiek, Fayette, Clayton, Dubuque 

 and Jackson. But, small as it is, it presents topographic features in some 

 respects more interesting than all the rest of the state together. As the 

 name implies, this area was not invaded by the ice sheets of any of the stages 

 of the glacial epoch. Its soils are largely residual, for they have resulted 

 directly, in place, from the decay of the local limestones, sandstones and 

 shales. Its topography is a product of erosion acting upon indurated rocks 

 of_varying degrees of hardness and varying degrees of elevation above base 



