GEOLOGICAL PAPERS. 



91 



Central Illinois Section. 

 For the region south of Rock Island, La Salle and Kankakee, and 

 north of the mouth of the Illinois River and Danville. 



"Coal measures," upper part; coal, shale, limestone, 

 and sandstone; 600-700 feet thick. 



"Coal measures," middle part; shale, sandstone, and 

 coal including approximately from "No. 2 coal" to 

 "No. 6 coal;" 300 feet thick. 



"Coal measures," basal part; (Pottsville equivalents), 

 including coal, claj', shale, and sandstone; mainly 

 the beds associated with the "No. 1 coals" of the 

 western part of the State, and of irreguar thick- 

 ness, found in deep borings elsewhere ; 50-150 feet 

 thick; small amounts of oil and gas reported, but 

 origin not certain. 



Unconformity. 



Carboniferous. 

 (Pennsylvanian.) 



Carboniferous. 

 (Mississippian.) 



Chester ; irregular thickness of sandstone, shale 

 and limestone, recognized in a few borings ; gen- 

 erally absent in this territory; 0-50 feet thick. 



Unconformity. 



St. Louis, Salem, Ste. Genevieve ; limestone, non- 

 magnesian, partly cherty and partly oolitic; 50-100 

 feet thick. Osage group, Warsaw, Keokuk, and 

 Burlington : shales and limestone, the latter often 

 cherty; 250-350 feet thick; crude petroleum in 

 geodes near the top of the Keokuk. 



Kinderhook; shales, limestones, and sandstones; 80- 

 150 feet thick. 



Unconformity. 



Devonian. 



Limestone; 15 feet thick. 

 L'nconformity. 



SoutJicrn Illinois Section. 

 For the area south of the mouth of the Illinois River and Danville, 

 including the principal oil and gas producing districts. 



Tertiarv. 



Lafayette, Porters Creek and Lagrange; sands, clays, 

 and ferruginous conglomerate found in extreme 

 southern counties only; 150 feet thick. 



Cretaceous. 



Riplev ; sands and clays in extreme southern portion 



of the State only ; 20-40 feet thick. 

 Unconformity. 



