STUART WELLER 



^:FVL 



through Monroe and into St. Clair 

 counties, successively overlap the 

 truncated Chester formations until 

 they rest upon the Ste. Genevieve 

 and St. Louis limestones whose 

 position is beneath the Chester. 



GEOLOGICAL HISTORY 



In order to appreciate properly 

 the historical relation of the Chester 

 series in the Illinois basin to the 

 Mississippian as a whole, it is 

 desirable to outline somewhat 

 briefly the succession of events 

 which are recorded in the Lower 

 Mississippian or Iowa series. The 

 stratigraphic units which are com- 

 monly recognized in this series in 

 the Mississippi Valley are as 

 follows : 



7 . Ste. Genevieve limestone 



St. Louis limestone 



Spergen limestone 



Warsaw limestone and shale 



Keokuk limestone 



Burlington limestone 



Kinderhook group 

 Throughout this basin the 

 oldest of the Mississippian forma- 

 tions belonging to the Kinder- 

 hook group rest unconformably 

 upon whatever beds underlie them, 

 unless possibly there may be a 

 continuity of sedimentation from 

 Devonian time in southeastern 

 Iowa. There is some reason to 

 believe that the oldest Kinderhook 



