302 COUNTY AND REGIONAL GEOLOGY. 



their way to its own channel. These tributary channels have 

 themselves shifted their locations from time to time, and even 

 now much of the flooding which the great plain suffers is 

 caused, not by the waters of the great river itself, but by 

 those of the tributaries which they bring down abundantly 

 from the western drainage slope of the State in rainy seasons. 

 It is true that the rise of water in the great river above, floods 

 thousands of acres of land, but there are other thousands of 

 acres which the highest floods of the principal stream do not 

 reach, and yet they are occasionally flooded by the tributaries 

 as they pour their waters down upon the great flood-plain. It 

 is especially these last named lands that may be reclaimed, 

 and in the further description of the physical features of this 

 flood-plain, a practical plan will be suggested for the attain- 

 ment of this important object. 



At or near the foot of the bluffs along a great part of the 

 whole length of the flood-plain in Iowa, there are remains to 

 be seen of an abandoned bed of the river channel, more 

 definite than those before mentioned which are seen to 

 traverse it. No doubt the river coursed along this now aban- 

 doned route several times during the long epoch that elapsed 

 while the valley was being formed, but the traces of the 

 channel that now exist there are doubtless those of the last 

 which the great river occupied there before it finally bore 

 away to the westward, leaving the greater part of the flood- 

 plain on the Iowa side, as it now exists. In Woodbury 

 county, above the point where the west fork of the Little Sioux 

 river comes through the bluff, these remains of the ancient 

 river bed consist of a series of ponds. From that point 

 southward, the west fork of the Little Sioux itself occupies 

 the ancient bed of the great river, until it forms its junction 

 with the principal branch of the Little Sioux, where the 

 waters of both branches occupy it until they are joined by 

 the Maple, all the time coursing along the base of the bluffs. 



From the last named point the waters of these united 

 streams reach the great river by a common channel, which 

 courses obliquely across the flood-plain and empties into 



