CARBOOTFEEOUS SYSTEM. 247 



assumes the character of true coal. It is of very fair 

 quality, but reaches only about twenty inches in maximum 

 thickness, and thus far it has been found exposed only in the 

 valley of the Nodaway river within the counties of Adams, 

 Montgomery, Taylor, and Page, and at one point in Fremont 

 county at the borders of the Missouri river valley. In the 

 four first named counties coal for domestic and manufacturing 

 use, has been taken from this bed, although it is so thin. In 

 Fremont county it is too thin and impure for any practical 

 use. 



Economic Value. The material furnished by this forma- 

 tion of value for economic purposes is confined principally 

 to its limestone. Wherever this stone is exposed it furnishes 

 good material for common masonry and also for lime. In 

 many places, excellent blocks also may be quarried for 

 dressing into caps and sills and other desired parts of the 

 better class of buildings. 



The prevailing color of the limestone is light gray, with 

 usually a tinge of blue. In Madison and Fremont counties, 

 the best layers are found for the purpose of dressing, and will 

 be mentioned in the descriptions of the geology of those 

 counties. The sandstones of this formation, so far as yet 

 observed, are usually shaly, and alway quite worthless. The 

 shaly and clayey beds have yielded to glacial action and 

 furnished material for the drift clays, and a part also of 

 the soil. No beds of clay, sufficiently pure for good pottery, 

 has been found in the whole formation, although it is so 

 abundant in some parts of the Lower coal-measures. Conse- 

 quently, potter's clay is scarce throughout the whole region 

 occupied by the Upper coal-measures in Iowa. 



Although this formation is known by the name of Upper 

 coal-measures, it has been shown that it contains but a 

 single bed of true coal, and that very thin. 



Fossils. The fossils of this formation are much more 

 numerous than they are in either the Middle or Lower coal- 

 measures, which is doubtless due largely to the fact that the 

 conditions of their living existence were more favorable 



