On the lower Paleozoic stratigraphy of southwestern Illinois / by T.E. Savage.

  • Savage, T. E. (Thomas Edmund), 1866-1947.
Date:
1908
Catalogue details

Licence: In copyright

Credit: On the lower Paleozoic stratigraphy of southwestern Illinois / by T.E. Savage. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    include the Cape Girardeau limestone and the overlying beds containing Dalmanites danae and Whitfieldella hillingsana. 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- gantxda, Homoiospira n. sp., Leptmia rhomboidalis, Rafines- guina rnesacosta, Rhynchotreta n. sp., Schuchertella missouri- ensis, Zygospira n. sp., Gornulites tenuistriata. 0. incurmts, Platyostoma near niagarensis, Strophostylus sp., Acidaspis halli, Calymene sp., Cyphaspis girardeaxtensis and Encrinu- rxLS sp. At the exposure north of Thebes the Cape Girardeau lime- stone rests dii'ectly upon the fossiliferous blue shale (fb of section). This member is succeeded by a bed of dark gray limestone, oolitic in the upper part, which contains Eavosites sp., Stroxnatopora sp., Atnjpa rugosa, Clox'inda n. sp., Ilomoe- ospira n. sp., cf. Ilindella umbonata, Leptcena rhoxixboidalis, Rlatystrophia bifox'ata., Rafinesquina rnesacosta., Rhyncho- treta n. sp., Schxtchex'tella subplanxbs (probably a coarse form of S. rnissouriexisis), Strophomena sp., Whitfieldella billings- ana, Dalmanites danae., Dalmanites sp., and Lichas bx'eviceps clintonensis. There are here no diagnostic fossils of the Richmond. The genera Eavosites, Stx'omatopora, Atxppa, Whitfieldella, Ho- moeospira, Schuchertella and Glorinda do not occur in Amer- ican Ordovician strata, while Atrypa rugosa and Lichas breviceps clintoxxensis 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. Schuchert* 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 Zc 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.