SUEFACE FEATURES. 65 



Maquoketa river has its course entirely upon the region 

 occnpied by the Magara limestone, and the character of its 

 valley is not unlike those of the Cedar and Wapsipinicon. 

 The magnesian limestone of this formation, however, weathers 

 into rougher and more irregular forms when exposed along 

 the banks and valley-sides, than the Devonian rocks of the 

 Cedar valley do, in consequence of which the valley of the 

 Maquoketa has frequently a more wild and romantic aspect 

 than those of the other rivers just named. The depth of the 

 valley, however, is not often great, seldom reaching two 

 hundred feet from the general level of the uplands, and the 

 valley-sides usually slope gently from them on both sides 

 of the stream. This river is more tortuous, and together 

 with its branches, it drains as great an area as the Wapsi- 

 pinicon, although it is much shorter than the latter. There 

 are many excellent mill-sites along the course of this 

 river. 



Turkey river. The Turkey and Upper Iowa rivers are 

 both in many respects quite unlike any of the other rivers of 

 Iowa hitherto described. The difference is principally due, 

 however, to the great depth to which they have eroded their 

 valleys, and the somewhat different character of the material 

 through which they have been eroded. Turkey river rises 

 within the State, and in comparison with its size it has a 

 shorter course than any of the others mentioned. In Winne- 

 shiek county, within a few miles of its source, its valley has 

 already attained a depth of more than two hundred feet from the 

 general level of the uplands; and in Fayette and Clayton 

 counties, its depth is increased to three hundred and even near 

 four hundred feet in some places . When the latter height above 

 the stream is attained, however, the slope of the valley-side 

 has carried it back to some distance. The summit of the up- 

 lands bordering nearly the whole length of the valley, is 

 capped by the Maquoketa shales, which, on account of their 

 friable character, seldom appear as natural exposures. These 

 shales are in turn underlaid by the Galena limestone, a 



magnesian limestone formation, which is here between two 

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