376 C. L. Fenton — The Devonian of Iowa. 



E. Summary. 



1, — The highest position in the Devonian of Iowa, as 

 well as the youngest, is occupied by a series of shales, 

 limestones and dolomitic beds reaching a maximnm thick- 

 ness of something over one hundred feet. 



2. — This formation rests npon some ninety feet of blu- 

 ish, clayey shale, here called the Sheffield Formation, 

 which is unrelated to it, and from which it is separated by 

 a rather poorly marked unconformity. 



3. — These hundred feet of shales, limestones and dolo- 

 mitic beds comprise a distinct stage, the Hackberry, with 

 a very rich and prolific fauna characteristic of this stage. 



Walker Museum, University of Chicago. 



