CARBONIFEROUS SYSTEM. 191 



characteristics are well shown. The coal-measnres rest con- 

 formably upon it in southern Illinois, where it attains a 

 thickness of eight hundred feet — a thickness greater than that 

 which the whole Sub-carboniferous group attains in Iowa. 

 Its most northern known limit is near Alton, Illinois, which is 

 a hnndred miles south of the most southern point in Iowa. 

 This formation received the name of Kaskaskia limestone in 

 the former geological report of Iowa, but the name here used 

 had been previously adopted by the geologists of the State 

 where it has been most studied, and ought therefore to be used 

 in preference to any other. 



As the Chester limestone has no direct connection with Iowa 

 geology, no description of it will be given in this report, but 

 the other formations of the group will be described separately 

 in the ascending order as before named. Xo attempt has 

 been made to define accurately the surface area occupied by 

 each formation of the Sub-carboniferous group in Iowa, 

 either upon the map or in the text, but a general idea of the 

 subject may be obtained from the separate descriptions 

 which follow. 



1. THE KLXDERHOOK BEDS. 



Syn — Chemung Group of several Authors. 



General Characters. This formation was referred to the 

 Devonian system in the former geological report of Iowa, 

 but its carboniferous characters are now recognized by almost 

 all geologists. Messrs. Meek & Worthern, of the Illinois 

 Geological Survey, recognized its characters as such, gave it 

 the name of " Kinderhook group,'' Irom the town of Kinder- 

 hook in the southern part of that State, where it is well 

 developed. Since the word group, as used in this report, is 

 so restricted in its meaning as to designate a group or 

 assemblage of formations, it is not deemed advisable to use in 

 this place the same word to designate one of the component 

 parts of a group as thus defined. To avoid this, and still to 

 recognize the priority of the name those gentlemen have applied 



