CKETACEOTTS SYSTEM. 291 



of this sandstone, it is with, few exceptions almost valueless 

 for economic purposes. The most valuable quarries in the 

 strata of this formation that have yet been observed, are at 

 Lewis, in Cass county, and in the northeastern part of Mills 

 county. At Lewis, it has a dark, brown color, and as it 

 hardens considerably upon exposure, it forms a very fair 

 building material, and being soft when first taken from the 

 quarry, it is wrought with great facility. Several buildings 

 have been constructed of it there, but the color is objectiona- 

 ble for ordinary dwellings, while it would be quite in 

 harmony with the Gothic architecture of small churches or 

 similar buildings, for which the stone at Lewis is sufficiently 

 durable, if well selected. 



The extensive denudation which this formation suffered 

 during the Drift epoch, has by its sand contributed to the soil 

 of that part of the State a warmth and mellowness that adds 

 largely to its productiveness and facility of cultivation, 

 without being sufficient in amount to cause it to approach 

 barrenness. 



Fossils. The only fossils found in the Nishnabotany 

 sandstone of Iowa, thus far, are a few fragments of Angio- 

 spermous leaves which are too fragmentary for identification. 

 The fossil corals before mentioned are of course not properly 

 fossils of this formation, as they belong to rocks from which 

 a part of the materials were derived of which the Cretaceous 

 strata are composed. 



3. THE WOODBURY SANDSTONES AND SHALES. 



These strata, as their name implies, are composed of 

 alternating sandstones and shales, the latter being sometimes 

 sandy, and sometimes clayey, with more or less calcareous 

 material intermixed. They follow next in order, and rest 

 upon the Nishnabotany sandstone. They have not yet been 

 observed outside the limits of Woodbury county which gave 

 them their name, but they are found there to reach a maxi- 

 mum thickness of about one hundred and fifty feet. The 



