332 Foerste — Ordovician- Silurian Contact in the 



and strongly curved anteriorly in a geniculate manner, in 

 addition to Rhynchotrevia capax and other fossils, 



The localities so far mentioned occur along the eastern line 

 of outcrop of the Clinton, where the position of the fossiii- 

 ferous layers, forming the top of the Madison bed, with refer- 

 ence to the Tetradium and Columnaria layers at its base, may 

 be determined by following these beds along practically con- 

 tinues lines of exposure. The fossil lists indicate the presence 

 in the upper part of the Madison bed of a considerable number 

 of fossils hitherto considered as confined to lower divisions of 

 the Richmond. There is evidently a recurrence of species 

 usually found more abundantly in the Whitewater bed. If the 

 existence of these species at the top of the Madison bed could 

 not be proved by following up practically continuous exposures 

 from Madison to the southeastern border of Ripley county, 

 and then up the Laughery to Versailles, Osgood, and Napoleon, 

 the occurrence of these species immediately beneath the Clin- 

 ton in the Ripley island area, farther west, at a considerable 

 distance from the continuous line of outcrop, would have been 

 considered as indicative of the presence of one of the lower 

 divisions of the Richmond, probably the Whitewater bed. 



Five miles west of Napoleon, a mile southeast of the north- 

 western corner of Ripley county, on Honey creek, Leptaena 

 rhomhoidalis, Strophomena vetusta, the Richmond group 

 form of Cyclonema bilix, and Calymmene callicephala are 

 added to the list of species already mentioned as occurring at 

 the top of the Madison bed. Rafinesqiiina altemata is found 

 in the white limestone, 3 feet thick, forming the top of the 

 Madison bed. Immediately below, Calymmene callicephala, 

 Plectambonites sericea, and a strongly convex species of 

 Dalmanella, only 13 mm wide, occur. The underlying beds, 

 consisting of thin irregular limestones weathered into frag- 

 ments and of greater quantities of clay, contain in addition to 

 species already named from this locality, Heberiella occidentalism 

 Hebertella near simiata, the Madison bed form of Platy- 

 strophia, Platystrophia acutilirita, Strophomena sulcata, the 

 large strongly curved form of Plectambonites, Rhynchotrema 

 capax, Protarea vetusta, Streptelasma rusticum, Streptelasma 

 divaricans, and Lophospira tropidophora. The form of 

 Byssonychia usually listed as B. radiata is present. The total 

 thickness of the fossiliferous section here is 20 feet. This in 

 itself would formerly have placed the reference of the Honey 

 creek exposure to the top of the Madison bed in doubt, but the 

 fossiliferous layers at the top of the Madison bed northeast of 

 Osgood have an equal thickness, and the exposures at Osgood 

 and near Napoleon carry practically the same fauna. 



At Zenas, 5 miles southwest of the Honey creek exposures, 

 the fossiliferous layers at the top of the Madison bed contain 



