FOURTH ANNUAL YEAR BOOK— PART II. l3l 



The curious peaks and knobs of the wind-drift topography, developed on 

 the bluffs facing the Missouri river, need only be mentioned. There is here 

 a perpetual contest between erosion and construction, which has resulted in 

 many erratic forms. This type of land surface is best seen in Iowa in a nar- 

 row belt extending from Sioux City to Hamburg. 



. DRAINAGE. 



The rivers of Iowa fall naturally into two systems — the Mississippi system 

 and the Missouri system. The headwaters of the two systems are separated 

 by the great divide. The Upper Iowa, or Oneota. has a more than usually 

 distinct drainage basin, for in its upper courses it is separated from the other 

 rivers of the eastern slope by the Cresco-Calmar ridge. Looking at the 

 irivers of the state as a whole, there are only a few points deservinjij special 

 mention. The streams and stream valleys of the driftless area are unique. 

 They are comparatively old. The waters began working on their present 

 channels before the beginning of the earliest glacial stage. The valleys, in 

 places ten or fifteen miles in width from crest to crest of the divides, have 

 been cut to depths of 500, 600, or even 700 feet. Near their mouths the 

 process of down-cutting, or corrasion, has brought the streams to base level, 

 and the walls of the valleys have receded so as to give broad alluvial flood 

 plains covered with what is probably the most productive soil in this great 

 fertile state. In the upper courses of the streams of the driftless area, and in 

 all the smaller tributaries , the gradients of the valleys are steeper , flood plains 

 are absent, adjustments are not yet perfect. In some portions of this area 

 the minor drainage is largely underground, a fact well demonstrated by the 

 numerous springs which pour out copious volumes of water along the hill- 

 sides and the steep river bluffs. In the area of the Kansan drift, water-cut 

 channels have been developed everywhere, and practically every foot of the 

 surface is thoroughly drained. None of the basins and sags which must 

 have been present in the original surface of the Kansan drift have been left 

 undivided. The whole area of this drift sheet, where not concealed by 

 younger deposits, is characterized by a miniature type of mature erosional 

 topography; but surface drainage has worked to best effect on the shorter 

 and steeper slope west of the great divide. Here the river valleys are 

 deeper and wider, and the numerously branched lateral channels have cut 

 back and become deeply entrenched in the higher plateaus. The rivers of 

 the lowan area have done but little work since they began to flow in their 

 present courses. Lateral drainage is not well developed; there are large 

 areas in which the surface remains just as it was left by the glaciers; not a 

 little of this surface is yet without effective means for getting rid of the sur- 

 plus storm waters. On the east slope of the great Cedar valley trough the 

 several streams drain areas which are remarkably narrow in proportion to 

 their length. Apart from the branches of the Des Moines river, there are no 

 important streams in the area of the young Wisconsin drift. Over the greater 

 part of the Wisconsin plain even the rudiments and beginnings of effective 

 drainage have not yet been established. 



The physical features of Iowa are conspicuously lacking in the rugged 

 and impressive types which characterize many of the states. The relief 

 forms are relatively tame. The scale on which they are designed is an 

 exceedingly modest one. What is lost in the matter of bold and massive 



