440 T. E. Savage — Stratigraphy of Southwestern Illinois. 

 Generalized section of the pre-Mississippian strata in soutluoesternlllinois. 





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Descriptions of horizons 



10c. Greenish-blue shale, fossils almost none 29 ft. 



10&. Black shale with few fossils, but carrying nu- 

 merous very small balls of iron pyrite from 

 1/8 to 1/2 inch in diameter 21 ft. 



10a. Brown to black, siliceous shale or shaly lime- 

 stone with Leiorhynchus globuliformis and 

 Reticularia Icevis 36 1/2 ft. 



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9c. Light gray, siliceous limestone, in part oolitic, 

 characterized by Chonetes coronatus, Cra- 

 noena romingeri, Spirifer pennatus, S. audac- 

 ulus, Tropidoleptus carinatus and Vitulina 

 pustulosa 7 ft. 



9b. Yellowish-brown siliceous or shaly limestone with 



few fossils 25 ft. 



9a. In the north are dark colored, fine-grained lime- 

 stones with Microcyclus discus, Chonetes yan- 

 dellanus, Eunella attenuata, Parazygahirsuta, 

 Spirifer fornacula and S. pennatus. In the 

 south are gray or leached limestones with 

 Athyris spirifer oides, Delthyris sculptilis, 

 Spirifer granulosus, Rhipidomella pcnelope 38 ft. 



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8a. Rather soft shale weathering to a yellowish- 

 brown color, with Leiorhynchus limitare 28 ft. 



This horizon is not present at the north, in 

 Jackson county. 







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7h. 



The Onondaga is well developed in Jackson 

 county, where it passes without a break into 

 the Hamilton. In the southern part of Union 

 county there is a break, and the Onondaga is 

 represented only by the basal sandstone 

 (7a of section). 



Heavy layers of very hard, gray, coarsely crys- 

 talline limestone, containing corals, Chonetes 

 konicManus, Pholidostrophia iowensis, Product- 

 ella spinulicosta, and Stropheodonta, concava. 

 Strophalosia truncata is abundant in the lower 

 half, while Produetella spinulicosta is common 

 in the upper part 26 ft. 



Layer of dark colored limestone largely com- 

 posed of Chonetes konicManus var 3 5/6 ft. 



