58 PHYSICAL GEOGRAPHY. 



different character from those of the western system. They 

 are larger, longer, and have their valleys modified to a much 

 greater extent by the underlying strata. For the latter 

 reason, water-power is much more abundant upon them than 

 it is upon the streams of the western system. 



The Des Moines river is almost entirely an Iowa stream, 

 having, it is true, its rise a few miles over the border in 

 Minnesota, but it enters Iowa before it has attained any con- 

 siderable size, and flows almost centrally through it from 

 northwest to southeast, emptying into the Mississippi at the 

 extreme southeastern corner of the State. 



As a river, it is more complete in itself than any other 

 of the Iowa rivers, except the Mississippi and Missouri, 

 draining a greater area, and being the largest and longest. 

 The upper portion of it is divided into two important 

 branches, called in the nsual nomenclature of the pioneers, 

 the East and West Forks. These nnite in Humboldt county 

 to form the main stream. The valleys of these branches 

 above their confluence are entirely drift-valleys, except that 

 a few comparatively small exposures of snb-carboniferous 

 limestone occur in the immediate banks of both streams, 

 from three to five miles above their confluence. But these 

 are not sufficient to even modify the general character 

 impressed upon the valleys by the Drift Deposit. They are 

 sufficient, however, to produce several fine mill-sites at those 

 points upon both the streams. 



The valleys vary in depth from fifty to one hundred and 

 fifty feet below the general prairie level. Their sides are 

 usually gently sloping, and they gradually blend with the 

 undulatory prairie surface of the upland. The beds are 

 more or less gravelly, but their banks are usually muddy 

 from the abundant fine material of the drift. The valleys 

 vary from a few hundred yards to half a mile in width; the 

 flood-plain is seldom well marked, but the bottom of the 

 valley is often a very gently sloping and slightly undulating 

 prairie, quite above the reach of the highest water, and, as 

 might be expected, are the finest of agricultural lands. 



