STRATIGRAPIUC TAXUKOMY (571 



the Tetragraptiis zone is not younger than the Nittany dolomite, and 

 that it may be older. 



Canadian deposits in tlie \V(dls Creek ba^n of Tennessee. — In the 

 Wells Creek l)asin, in northwestern middle Tennessee, named and 

 briefly described by Safford/*^*^ the low dome-like elevation at the center 

 of the small but sharply defined nplift is formed by a highly cherty 

 magnesian limestone of Canadian age, but undetermined thickness. The 

 prevailing type of the chert, w^hich strews the surface and with a deep 

 residual clay covers the light gray, fine grained, magnesian limestone 

 from which it is derived, is porous — even spongy — rather soft and sandy 

 under the hammer, and red or brown in color. With these occur harder,' 

 nearly white blocks. This cherty magnesian limestone is overlain — not, 

 as one might naturally suppose, by some Stones Eiver limestone, but by 

 Lowville limestone. Owing to concealing cover at the critical point, the 

 contact was not observed. The Lowville as usual closely resembles the 

 Lebanon, and had hitherto been mistaken for that Stones Elver forma- 

 tion. But the discovery of Tetradium cellulosum and other reliable 

 Lowville fossils enables us to correct a misapprehension and at the same 

 time to establish an interesting and unexpected hiatus. 



Some of the chert is highly fossiliferous. Slender gastropods of the 

 genera Hormotoma and CoeJocaulus are especially abundant. Other 

 genera of the same class, like OpMleta (of. 0. levata), Helicotoma, and 

 Holopea are also represented. Then there is a small Ortlioceras, like 

 0. primogenivm. a Protocydoceras. a slender SaUerella?, Cameroceras 

 8p., Cyrtoceras cf. confertissimum, Machirea emmonsif. an Orthoid like 

 0. electra, a striated Syntrophia . and an Isochilina resembling 7. armata 

 of the Lowville. 



The general aspect of the fauna (more than half of the species are 

 identical) is decidedly like that found in the upper part of the Ceratopea 

 bed of the Yellville formation in northern x\rkansas. As there is further 

 notable agreement in lithologic characters, T have no hesitancy in cor- 

 relating the two horizons. As a distinct name for this cherty zone of the 

 Canadian rocks in the Mississippi Valley is desirable, especially in Ten- 

 nessee, the name Wells chert is here proposed. 



Canadian UmeMone in the fiontheni Appalachian Valley — Character 

 and extent. — Thin to moderately thick-bedded, usually fine grained and 

 in part magnesian limestone of Canadian age is found rather generally in 

 the eastern or Athens trough south of Lexington, Virginia. Tn soutli- 

 western Virginia and in east Tennessee as far south at least as Greenville, 



i"oj. M. Saflford : Geologj- of Tennessee. 1860, p. 147. 



