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



include the Cape Girardeau limestone and the overlying- beds 

 containing Dalmaiiites danae and Whitfieldella billingsana. 

 The Cape Girardeau limestone is well exposed about two miles 

 south of Thebes, in the bank of the river and along the streams 

 in that immediate vicinity. It is also seen in a cut along the 

 Illinois Central railroad, and in the river's bank, one and one- 

 half miles north of Thebes. In the former locality this lime- 

 stone is nearly 40 feet thick, and consists of black, fine-grained, 

 brittle limestone, in thin layers which are often separated by 

 narrow partings of dark, calcareous shale. This zone has a 

 rich fauna which appears abruptly at this horizon. Among 

 the forms are several species of crinoids, Dalmanella near ele- 

 ganttda, Homceospira n. sp., Leptcena rhomboidalis, Rafines- 

 quina mesacosta, Rhynchoireta n. sp., Schuchertella missouri- 

 ensis, Zygospira n. sp., Cormdites tenuistriata, G. incurvus, 

 Platyostoma near niagarensis, Stropho stylus sp., Acidaspis 

 halli, Calymene sp., Cyphaspis girardeauensis and Encrinu- 

 rus sp. 



At the exposure north of Thebes the Cape Girardeau lime- 

 stone rests directly upon the fossiliferous blue shale (2b of 

 section). This member is succeeded by a bed of dark gray 

 limestone, oolitic in the upper part, which contains Favosites 

 sp., Stromatopora sp., Atrypa rugosa, Clorinda n. sp., Homce- 

 ospira n. sp., cf. Hindella ■umbonata, Leptcena rhomboidalis, 

 Rlatystrophia biforata, Rafinesquina mesacosta, Rhyncho- 

 treta n. sp., Schuchertella subplanus (probably a coarse form 

 of S. missouriensis), Strophomena sp., Whitfieldella billings- 

 ana, Dalmanites dance, J)alma?iites^s,])., and Lichas breviceps 

 clintonensis. 



There are here no diagnostic fossils of the Richmond. The 

 genera Favosites, Stromatopora, Atrypa, Whitfieldella, Ho- 

 mceospira, Schuchertella and Clorinda do not occur in Amer- 

 ican Ordovician strata, while Atrypa rugosa and Lichas 

 breviceps clintonensis are indicative of the Silurian. On the 

 other hand, the fauna is not directly related to that of the 

 Clinton, from which formation it is separated by a marked 

 erosional unconformity. Sehuchert* cites a fauna from Edge- 

 wood, in eastern Missouri, collected by Ulrich, which corre- 

 sponds closely with the above. Since there seems to be no 

 direct time equivalent of these beds in the Ordovician or in 

 the Silurian as generally defined, the horizons Za to 3c are 

 classed as Middle Silurian strata that more or less completely 

 bridge the lost interval between the Cincinnatian and the 

 Clinton. For these beds the time term Alexandrian is pro- 

 posed, from Alexander county, Illinois, where they are well 

 exposed ; the term to have the same rank as Cincinnatian, 

 which it immediately follows. 



* Jour. Geol., vol. xiv, pp. 728, 729, 1906. 



