52 PHYSICAL GEOGRAPHY. 



the Great Watershed in this part of the State, along which 

 portion of its course it has well-defined borders, and a width 

 of from one quarter to half a mile. Even here, where the 

 valley is so deep, nothing hut drift is to he seen in its hottom 

 or sides, from which fact it is inferred that the Drift Deposit 

 is ahont two hundred feet thick at this point. Just as the 

 valley enters Cherokee county it turns to the southward, and 

 becomes much widened and has its sides usually gently 

 sloping to the uplands, which gives it the appearance of 

 being shallower than it is farther up; but this is really not the 

 case. When the valley enters the region of the Bluff Deposit, 

 the surface soon begins to assume that billowy appearance 

 before described, and its borders are consequently more or 

 less obscured; yet it retains a general depth of about two 

 hundred feet from the adjacent uplands until it joins the 

 valley of the Missouri. 



The lower portion of the river, from the last named point, 

 is wholly unlike any other part of it; but is like similar 

 portions of every other stream that crosses the great flood- 

 plain within the State. It is a narrow, sluggish ditch, which 

 is frequently filled with back-water from the Missouri river, so 

 as to cause an overflow of the water of the upland portion 

 of the stream upon the flood-plain. Indeed, the lower 

 portions of these streams are only accidental channels for 

 the escape of their waters to the great river across its flood- 

 plain. 



The Missouri river in former times ran along the foot of 

 the bluffs on the Iowa side of its valley, where traces of its 

 channel still remain. The Little Sioux now flows along a 

 portion of the old channel of the great river, where it unites 

 the West Fork, the Little Sioux, and Maple rivers into a 

 common channel as they successively come down upon the 

 uplands. Formerly these were independent streams and 

 each emptied directly into the Missouri river. No exposures 

 of strata of any kind have been found in the valley of the 

 Little Sioux nor in those of its branches. 



Floyd river is a small stream, essentially like those just 



