41 6 STUART WELLER 



limestone of western Kentucky and southern Illinois from the 

 underlying Ste. Genevieve Kmestone. The Renault, or Renault- 

 Shetlerville, actually lies unconformably upon the Ste. Genevieve 

 in the sections examined by Ulrich, with the Aux Vases sandstone 

 of the Mississippi Valley section wanting. The characteristic 

 Chester fauna of the Renault limestone, mistakenly included in 

 the Ste. Genevieve by Ulrich, led him to assign the whole of the 

 Ste. Genevieve to the Chester. Although there is some passing 

 of species from the Ste. Genevieve into the basal Chester, long 

 experience in the field has demonstrated that the really character- 

 istic Ste. Genevieve fossils species do not pass into the Renault or 

 basal Chester, and long-continued faunal studies based upon 

 extensive collections have shown that by far the most important 

 faunal break in this portion of the stratigraphic sequence occurs 

 in passing from the Ste. Genevieve limestone to the overlying 

 Chester, This important faunal break, associated with the uncon- 

 formable relation of the Chester sediments upon the underly- 

 ing formations, wherever this portion of the section is exhibited, 

 and also associated with the distinct change in sea-pattern in 

 passing from the Ste. Genevieve to the Chester in the Illinois basin, 

 seems to afford an abundance of evidence of various sorts for 

 placing the major Hne of division within the Mississippian at the 

 top of the Ste. Genevieve limestone. In the Mississippi River 

 counties of Illinois this line is at the base of the Aux Vases sand- 

 stone, while in the more southern counties of the state it is at the 

 base of the Shetlerville-Renault limestone unit. The two so 

 constituted divisions of the Mississippian are of sufficient im- 

 portance to rank as series, the Mississippian as a whole constitut- 

 ing a system. 



{Concluded^ 



