SURFACE FEATURES. 61 



destined to become the seat of extensive manufactures, both in 

 consequence of their numerous mill-sites of immense power, 

 and the fact also that the main valley traverses the entire 

 length of the Iowa coal-field. 



Skunk river runs almost its entire course, after it has 

 reached any considerable size, upon the border of the outcrop 

 of the Lower coal-measures, or perhaps more properly 

 speaking, upon the sub-carboniferous limestone, just where it 

 begins to pass beneath the coal-measures by its southerly 

 and westerly dip. Its general course is nearly due southeast, 

 and its slope being nearly coincident with the dip of the 

 formation upon which -it runs, its valley is not strongly 

 marked by outcrops of strata, except along the lower part of 

 its course in Henry and Des Moines counties. Here the 

 limestone forms frequent cliffs from twenty to fifty feet high, 

 but it is only in the immediate valley that any exposures 

 appear, because the whole country elsewhere is covered with 

 drift. 



From the western part of Henry county, up as far as Story 

 county, the valley of Skunk river has been a terror to trav- 

 elers from the earliest settlement of the country until the 

 introduction of railroads. It was the broad flat flood-plain 

 that formed the obstruction to travel, for it is covered with a 

 rich, deep, clayey soil, which in times of long continued rains 

 and overflows of the river, made the whole a bed of adhesive 

 mud, through which men and animals could pass only with 

 great difficulty. The sides of the valley are usually so gently 

 sloping along this part of its course, that it has the appear- 

 ance of being very broad and shallow. The stream has 

 really a considerable current, and the table on a previous 

 page shows its slope also to be considerable; yet, as viewed 

 from the uplands, it appears to be a sluggish stream, as it 

 meanders through its broad flood-plain, with its slightly 

 raised and muddy banks, bordered by willows, or a few 

 scattered elms. 



There are some excellent mill-sites on Skunk river, espe- 

 cially upon the lower half of it, but usually they are not so 



