GEOLOGICAL PAPERS. 101 



Correlation : In the foregoing list of fossils only thirteen 

 species are certainly identified. Of this number, Hal^'sites caten- 

 ulatus and Lcptaena rhomboidalis have no definite stratigraphic 

 value. Atrypa niarginahs, Atrypa piitilla, Dalmanella elegantula 

 var., and Rhynchotrcta thcbesensis occur also in the Edgewood 

 strata of southwest Illinois. Atrypa marginalis and Dalmanella 

 elegantula have also been reported from the Clinton bed at CHf- 

 ton, Tennessee. 



Of the remaining seven identified species, Camarotoechia f 

 cliftonensis, Pentamerella f manniensis and Rhynchotreta simplex 

 were described by Foerste from strata that he considered of 

 Clinton age. at Clifton and near Riverside, in western Tennessee, 

 where they were said to occur with such other typical Ohio Clin- 

 ton species as Triplecia ortoni, and Illaenus da^'tonensis. IVhit- 

 fieldella cylindrica and Alytilarca mytilifonnis were described by 

 Hall from the Clinton strata of New York. Rhipidomella hybrida 

 and Schuchertella subplana are common species of the Niagara 

 limestone. 



The above analysis of the fauna of the Essex limestone would 

 seem to indicate a Clinton age for these strata. However, in this 

 fauna, the typical species of the Ohio Clinton fossils are wanting, 

 and the characteristic fossils of the New York Clinton are absent. 

 In southwest Ilhnois there are present normal Ohio Clinton strata 

 containing fossils similar to those found in the corresponding beds 

 in Ohio ; but such characteristic fossils of the Essex limestone, as 

 Camarotoechia ? cliftonensis, Pentamerella ? manniensis, and 

 Rhynchotreta simplex do not occur either in southwest Illinois or 

 in the Clinton beds in Ohio. Since the normal Ohio Clinton fauna 

 is present in the Clinton strata of Ohio and southern Illinois, but 

 is absent in the Essex limestone in which Camarotoechia ? clif- 

 tonensis, Pentamerella ? manniensis and Rhychotreta simplex are 

 common, it seems strange that the faunas of the Ohio Clinton 

 and of the Essex limestone should be intermingled in the Clinton 

 bed at Clifton, Tennessee. That the Essex fauna entered the 

 Mississippi valley from the south, as did also the Ohio Clinton, is 

 indicated by its presence in Illinois and in western Tennessee, and 

 its absence east of the Cincinnati arch. The Pentamerella ? man- 

 niensis horizon has also been found at an intervening point in 

 Jersey county, Illinois. 



In view of these facts, it is difficult to understand how such an 

 important element of the Essex fauna could be mixed with the 



