GUELPH FAUNA IN THE STATE OF NEW YORK 1 37 



of green argillaceous shales which doubtless pertain to the Salina stage. 

 The Cobleskill or Coralline limestone fauna was early described by Hall 

 who regarded it the eastern representative of the Niagaran group as then 

 known in western New York. He interpreted the underlying shales as of 

 Clinton age. Recent examination however clearly indicates that the Cobles- 

 kill limestone as shown in the section described pertains to an age later 

 than Salina, as has been suggested by Schuchert. 



One of the marked differences between the faunas of the Niagaran of 

 New York and the Cobleskill is the presence in the latter of quite an exten- 

 sive gastropod and cephalopod fauna — one of the features which strongly 

 affiliates it with the Guelph. And, indeed, Hall, in the original descriptions 

 of Pleurotomaria subdepressa and Murchisonia terebra- 

 1 i s, notes in each case a similarity to forms described from the Guelph. 



An interesting feature of some of the gastropods from the Cobleskill 

 is that in form they are sinistral. Pleurotomaria subdepressa 

 mentioned above belongs to this class. Another species is distinguished 

 from Poleumita crenulata Whiteaves (Guelph), only by its sinistral 

 form. Other specimens of the genus Pleurotomaria have been found which 

 in size and form are similar to the Guelph species, but the delicate surface 

 markings often so well preserved in the Guelph dolomites and upon which 

 specific determinations to a certain degree are dependent, have not yet been 

 ascertained in the Cobleskill limestone specimens and thus specific compari- 

 sons become unsatisfactory. Kionoceras darwini Billings occurs at 

 Schoharie, and in the western extension of the Cobleskill fauna on Fronte- 

 nac island, Cayuga lake, where Orthoceras trusitum Clarke & 

 Ruedemann and Gomphoceras septoris Hall (Guelph) are also 

 found. In Schoharie county mature specimens of Ilioniagaltensis 

 Whiteaves occur. Associated with them are forms which in outline and 

 dimensions approach Ilionia canadensis Whiteaves and to that 

 species they are provisionally referred. Spirifers from the Guelph have 

 obsolescent plications and a sinus similar to Spirifer crispus var. 

 corallinensis Grabau. 



There are other species common to these faunas but they are mostly 

 forms occurring also in the Niagaran and indicative solely of a late Siluric 

 stage. 



