218 GENERAL GEOLOGY. 



The three lowest members of this section and their geological 

 equivalents elsewhere were designated by Prof. Hall in the 

 former geological report of Iowa as a distinct formation, 

 under the name of " Warsaw limestone," but as there seems 

 to be no sufficient reason for such a separation, they are 

 in this report all referred to the epoch of the St. Louis 

 limestone, and the use of the name Warsaw limestone dis- 

 discontinued. The bluish argillaceous shales which so 

 prominently characterize the exposures of this formation 

 at Warsaw are scarcely recognizable in Iowa, even upon 

 the opposite bank of the river ; so that only the three 

 divisions before mention are recognized in our State. 



The upper division, consisting of the compact concretionary 

 limestone, is the one most commonly met with, but both the 

 magnesian and sandy divisions are frequently found in con- 

 nection with it, and are seen even at those northern localities 

 in Hamilton and Webster counties. The maximum thickness 

 of the whole formation in Iowa, including its three divisions, 

 is about seventy-five feet. The upper calcareous portion, 

 especially in southeastern Iowa, is usually capped with 

 several feet in thickness of grayish, fossiliferous, marly clay, 

 and similar material often forms partings between the layers 

 of limestone. This portion reaches a maximum thickness of 

 about thirty -five feet. The sandstone, or middle division, 

 reaches a thickness of twenty feet at Keosauqua, but it is 

 usually thinner. It is sometimes shaly, but usually a clear- 

 grit sandstone, and has been distinctly recognized in Lee, 

 Van Buren, Mahaska, Webster, and Hamilton counties. The 

 lower, or magnesian division, although generally consisting 

 of a tolerably pure magnesian limestone, sometimes has a 

 part of its layers sandy or shaly. It reaches a maximum 

 thickness of about twenty feet. 



During the time of the deposition of this formation, there 

 seems to have been some slight disturbance of the strata, 

 apparently amounting only to local disarrangements of its 

 own layers. This is principally shown in the upper division 

 and consisted in the slipping, bending, or slight distortion of 



