120 ILLINOIS ACADEMY OF SCIENCE 



2, in his Randolph County section, immediately superjacent 

 to the Cypress sandstone, was described as a "compact gray 

 limestone, with intercalations of blue, green and purple clay 

 shales," 150 feet thick. The more detailed studies have shown 

 this bed to be a composite member, made up of several dis- 

 tinct formational units, with an aggregate thickness con- 

 siderably greater than estimated by Worthen. The Cypress 

 sandstone also, as interpreted by Worthen. proves to be a 

 composite member the higher beds comprising a distinct for- 

 mation which rests unconformably upon the lower. 



These detailed studies have necessitated the recognition 

 of a series of nine distinct formations in the Chester group, 

 which are designated as follows : 



9. Clore formation. 



8. Palestine formation. 



7. Menard formation. 



6. Okaw formation. 



5. Ruma formation. 



4. Paint Creek formation. 



3. Yankeetown formation. 



2. Renault formation. 



1. Brewerville sandstone. 



Each of these formations possesses distinct lithologic and 

 faunal characters by which it may be easily recognized, and 

 all of them may be readily traced and mapped throughout 

 the region studied. UlriclVs division of the supra-Cypress 

 portion of the Chester into the Tribune and Birdsville forma- 

 tions has not been carried out in detail by him in the Ran- 

 dolph and Monroe county area, but he has stated (7) that 

 he considers the summit of the limestone ledge quarried in 

 the Southern Illinois Penitentiary near Chester, to be the 

 dividing line between the Tribune and Birdsville. Under 

 this interpretation the Tribune of Ulrich would include the 

 Okaw, the Ruma, the Paint Creek, the Yankeetown and part 

 of the Renault formations, leaving the INIenard, the Pales- 

 tine and the Clore as the equivalent of the Birdsville. Fur- 

 thermore, all the formations from the summit of the Okaw 

 downward to some point within the Renault, have been dif- 

 ferentiated from Worthen's 150 foot limestone member im- 

 mediately superjacent to the basal sandstone or Cypress 

 member in his Randolph county section. It will be under- 

 stood from this statement, therefore, that the most important 

 results of these recent studies have been in magnifying the 

 importance of the lower portion of the Chester group, these 

 members of the group having their more typical development, 

 not in the Mississippi River blufYs, but in the region between 

 the Mississippi and the Okaw or Kaskaskia valleys. 



