Wincliell.] 'J^" [May 6, 



stratigraphical and litliological conformity in the two series of sandstones 

 (besides Goniatites Oiceni, common to Nortliei-n Michigan and Indiana, 

 Chonetes Illinoisensis, common to Nortlieni Michigan, Ohio, Indiana and 

 Iowa; Gardtopsis megambonata, common to Northern Michigan and Iowa, 

 and Goniatites Shumardanus, common to Northern Michigan and Ohio), 

 I think tlieir geological equivalency can never hereafter be called in 

 question. 



In conducting the palseontological branch of the discussion of equivalen- 

 cies among the western districts, it would be appropriate to cite here the lists 

 of species identified in two or more of these districts. As this, however, 

 would considerably extend the limits of this paper, and these lists are readily 

 deducible from the "Catalogue" given, I present only the summaries. 

 In doing this, I shall count the two Michigan districts as one, and shall 

 also omit Kentucky, since I feel some uncei-tainty about the geological 

 position of the two species recorded from that State. 



Should we unite Producta Shumardana and P. pyxidata with P. eon- 

 centrica, the latter species would be known in seven different Western 

 States, besides the Pt. aux Barques region. 



With such an extended network of identifications, and with long lists 

 of representative species which I forbear to cite, I believe it will be ad- 

 mitted that the several formations brought under comparison must have 

 been accumulated in one geological period. Let it now be distinctly stated 

 what are the formations which are thus synchronized. They are as fol- 

 lows : 



