CAKBONIFEEOTTS SYSTEM. 245 



referred to further on in this chapter, under the head of 

 Fossils. 



The question is one not only of great scientific interest, but 

 one also of the greatest practical importance to the people of 

 the State. If the views formerly entertained by some geolo- 

 gists and others are correct, there is no hope of finding 

 profitable beds of coal in the western part of Iowa, at any 

 depth; but as the relative positions of the formations are 

 now understood, it is reasonable to expect that we may reach 

 profitable beds of coal by sinking shafts there at considerable 

 but not impracticable depths. The question is further dis- 

 cussed under the head of Practical Conclusions at the close of 

 this chapter. 



The prominent lithological feature of this formation 

 as before intimated is its limestones, yet it nevertheless 

 contains a considerable proportion of shales and sandstone. 

 The latter is usually fine grained and shaly, and the shales 

 are often somewhat sandy, mica in minute quantity being 

 usually present in the sand. The shales are largely com- 

 posed of clayey material, but are also alwa}^s more or less 

 calcareous, so much so, sometimes, that they show little trace 

 of stratification, become somewhat concretionary, and may 

 with propriety be called marls; or, when more indurated, as 

 they often are, the term marlite has been sometimes used to 

 designate them. These marlites, which are usually partings 

 between layers of limestone, but often form beds of consid- 

 erable thickness, are sometimes very fossiliferous. 



The accompanying lithograph, represents a section of Upper 

 eoal-measure strata in the order in which they are found 

 exposed in the valley side of Middle river at Winterset, in 

 Madison county. The exposures here are so extensive that 

 the strata comprise the greater part of the vertical thickness 

 of the whole Upper coal-measure formation in Iowa, so far 

 as any opportunity has existed for measuring them, and 

 yet the locality is only about ten miles from the border of the 

 area occupied by the formation. 



This section may be considered a typical one then, for 



