1 18 ILLINOIS ACADEMY OF SCIENCE 



The purpose of this paper is simply to suggest lines along 

 which practical use may be made of cloud observations that 

 any intelligent person with opportunity to view the sky may 

 readily make for himself. 



STRATIGRAPHY OF THE CHESTER GROUP IN 

 SOUTHWESTERN ILLINOIS. 



STUART WELLER* 



Introduction. 



The earlier work on the stratigraphy of the Chester 

 group in southern Illinois was done by Swallow, (1) Hall, (2) 

 EnjE^elmann. (3) and Worthen. (4) No attempt will be made 

 in this place to review in detail the work of these several, 

 observers. It is sufificient to state that after the publication 

 of Worthen's reports of the Geological Survey of Illinois, a 

 fairly well defined series of rock strata, at the summit of the 

 so-called Sub-Carboniferous or Lower Carboniferous series, 

 having their typical development in Randolph County, were 

 commonly known as the Chester group. Hall had applied 

 the name of Kaskaskia to the greater part of the same series 

 and the names Kaskaskia and Chester were commonly con- 

 sidered as being synonymous. Rocks having similar litho- 

 logic characters and with the same fossils, were recognized in 

 other states further south, notably in Kentucky and Alabama, 

 and the same names, either Chester or Kaskaskia were applied 

 to them- The total thickness of the rock strata to which these 

 names were applied was 800 or more feet. 



No serious attempt was made to subdivide this Chester 

 group until the publication by Ulrich and Smith of a report 

 on "The Lead. Zinc and Fluorspar Deposits of Western 

 Kentucky" in 1905 (5). In this report Ulrich proposed to 

 divide the entire group into three major formations, the Ste. 

 Genevieve limestone below, the Cypress sandstone, second, 

 and the Kaskaskia limestone above. The name Ste. Genevieve 

 had been used by Shumard (6) for a limestone in Missouri, 

 which comprised a part of the Ste. Genevieve of L^lrich. (6) 

 The name Cypress had been proposed by Engelmann in the 

 same sense as used by LHrich, this sandstone being the basal 

 member of the Chester group of \A^orthen. Kaskaskia was 

 a revival of Hall's name which was originally applied to the 

 beds lying above the Cypress sandstone of Engelmann. The 



* Published by permission of the Director of the Illinois State 

 Geological Survey. 



