378 COUNTY AND REGIONAL GEOLOGY. 



of the latter valley which lies within Pottawattamie county, 

 however, is merely that of a prairie stream, but there are 

 considerable bodies of woodland in the southern half of it. 



The greater part of the surface of the county has a con- 

 siderable degree of monotony in general aspect, owing to 

 the extensive prairie surfaces, but the region adjacent to 

 the valley of the Missouri river, along the whole western 

 border of the county, is one of strange and interesting 

 beauty, the most conspicuous features of the landscape 

 being the broad fertile flood-plain of the Missouri river 

 and the continuous range of bluffs that border it, all of 

 which have been already described. 



Geology. Owing to the great depth of the Bluff Deposit, 

 exposures of strata are very few, but all the strata of the 

 county immediately beneath the surface deposits are, without 

 doubt, of Upper coal-measure and Cretaceous age. Only one 

 exposure of rocks of the latter age has been observed within 

 its limits. This is in the valley of the East JSTishnabotany, 

 near the southeast corner of the county, on section 36, town- 

 ship 75, range 38. Its full exposed thickness at this point 

 is about thirty feet, and the continuous front of the exposure 

 is several hundred feet in length. The stone is the usual 

 yellowish, coarse-grained sandstone, too soft here for any 

 practical use. 



No exposures of Upper coal-measure strata were found in 

 the valley of the East Mshnabotany in this county, although 

 several extensive ones occur in the same valley in Cass 

 and Montgomery counties, not far distant. In the southern 

 part of the county, on section 21, township 74, range 40, near 

 Fig. 42. the left bank of the West Mshnabotany, 



3 v^_ »— ;^=? /o" there is a small exposure of the Upper 

 coal-measure strata. The exposure is 

 near Macedonia post office, and a little 

 below Stutsman's mill, and is repre- 

 sented by Fig. 42. 



