336 New York State Museum 



dant and were favorable for the existence of life under 

 new conditions and environment. The Upper Guelpb 

 horizon at Rochester and Shelby is characterized by fos- 

 sil-bearing chert concretions. With increasing salinity 

 the Guelph fauna, an invasion from the west, replaced 

 the Lockport fauna and finally itself disappeared with 

 the formation of the Salina sea. Two types of structure 

 are represented in the Guelph fauna : large, heavy-shelled 

 forms that occupied the more exposed areas of the coral 

 reefs and small, thin-shelled forms that lived in more 

 sheltered places (Lockport and Rochester forms mostly 

 here). Characteristic Guelph fossils are the hydrocoral- 

 line Stromatopora galtensis, the brachiopod Monomorella 

 noveboracum, the gastropods Poleumita scamnata and 

 Hormotoma whiteavesi and the cephalopods Trochoceras 

 desplainense and Poterioceras sauridens. Among the 

 earlier forms that have carried over are the corals Fa- 

 vosites niagarensis, Halysites catenulatus, the brachiopods 

 Dalmanella cf. elegantula, Rhipidomella cf. hybrida 

 Spirifer crispus, and the trilobite Calymene niagarensis. 



The Cayugan series (Clarke and Schuchert '99) con- 

 stitutes the Upper Silurian, and includes the Salina beds, 

 Cobleskill limestone, Rondout zuaterlime and Manlius 

 limestone. Since the upper members are typically ex- 

 posed along the north end of Cayuga lake and all the 

 members cross Cayuga county, that name was assigned 

 to the series. 



The Salina beds (Dana '64) are the "Salina shales" of 

 earlier authors and the present named divisions practic- 

 ally correspond to the four members of the reports of 

 Vanuxem and Hall, who designated the whole group as 

 the "Onondaga Salt group." The Salina beds occur in 

 two belts in New York. The larger one extends in 



