48 PHYSICAL GEOGRAPHY. 



Tlie characters of these valleys receive very little modifica- 

 tion from the presence of the Drift Deposit, yet they do not 

 differ very greatly from the drift-valleys in general appearance, 

 more especially along their npper portions. Both these 

 rivers have a few exposures of the underlying strata in their 

 valleys, but they occur only along their middle portions 

 above their confluence. These do not, in consequence of the 

 great thickness of the surface deposit, modify the character 

 of the valleys to any extent. The West Nishnabotany is 

 probably without any valuable mill-site, although it has a 

 few slight exposures of Upper coal-measure, limestone, and 

 Cretaceous sandstone in its valley. These occur only in the 

 southern part of Pottawattamie county and in the western 

 part of Mills county. 



In the western part of Cass county, the East Mshnabotany 

 loses its identity by becoming abruptly divided up into live 

 or six different creeks, near which point several exposures of 

 the Upper coal-measures, and a few also of Cretaceous sand- 

 stone are found in their valleys, and also in that of the 

 main Nishnabotany. A few exposures of the same rocks 

 are also found at rare intervals below the point referred to, 

 in the counties of Pottawattamie, Montgomery, and Page. 

 A few good mill-sites occur on this stream in the western 

 part of Cass county, near the exposures of stata before 

 mentioned; but none that are thought to be really reliable, 

 exist on either of these rivers or on the main stream below 

 the confluence, except perhaps, one or two in Montgomery 

 county. 



The general appearance and character of the valleys of 

 these two rivers from their sources to the middle, respectively, 

 of Cass and Pottawattamie counties, are those of ordinary 

 prairie creeks, or of valleys excavated in the drift alone. 

 The valley sides are gently sloping and undulatory like those 

 of such streams; but below the points named they begin to 

 assume their peculiar characteristics. The valleys gradually 

 widen to a width of from a quarter of a mile to one or two 

 miles, or even more; their sides being still undulatory and 



