XII INTRODUCTION. 



longs to that portion of the Upper Silurian forming the " Shaley 

 limestone" division of the Lower Helderberg group, to which 

 Dr. Shumard had correctly referred these beds in the Missouri 

 Report. Among the fossils collected by us here, there are forms 

 we cannot distinguish from the following New York "Shaley 

 limestone" species, viz : Orthis subcarinata and 0. obJata, Hall ; 

 Coelospira concava and C. imbricata, Hall ; Spirifer perlamellosus, 

 Hall ; Platyceras spirale, Hall ; P. Gebhardi and Acidaspis hama- 

 tus, Conrad. We also found there species scarcely, if at all, 

 distinguishable from the "Shaley limestone" species, Merista 

 princeps, Platyceras pyramidatum, P. unguiforme, P. incile and 

 P. multistriatum, Hall. 



Farther down the river, in the southern part of Perry county, 

 Missouri, the hills, for over two hundred and fifty feet in height, 

 are composed of the same beds seen at Bailey's Landing, and 

 the cherty beds we now include as a part of the Oriskany 

 group, all dipping to the eastward. We found only a few 

 fragments of fossils here, however — barely enough to assure us 

 of the identity of the strata. 



On crossing over into Union county, Illinois, in the region 

 of Jonesboro', we had an opportunity to examine the cherty 

 beds alluded to above, and found them characterized (with the 

 exception of Platyceras Gebhardi) by an entirely different group 

 of fossils from those seen near Bailey's Landing, and still farther 

 confirming the conclusion that these beds belong to the Oriskany 

 period. Including those collected by Mr. Engelmann, and a 

 few that were collected by one of us from these beds in Jack- 

 son county, together with those found during our late exami- 

 nations, we can safely give the following list of well-known 

 Oriskany species, as occurring in this formation in Southern 

 Illinois, namely: Leptoccelia fiabellites (sp.), Conrad; Leptmna? 

 nudeata, Rhynchonella speciosa and Platyceras tortuosum, Hall ; 

 with Eatonia peculiaris and Platyceras Gebhardi, Conrad. These 

 are associated with Rensselwria Condoni, McChesney, which, 



