REPORT OF THE STATE PALEONTOLOGIST I903 357 



tions however which are found and which show the intimate 

 relation of the two formations are as follows. 



In western New York usually underlying the Oriskany sand- 

 stone is found the Cobleskill dolomite which at Buffalo, Dr 

 Grabau^ has shown, contains a fauna similar to the Cobleskill 

 and which later studies have shown to be identical with the 

 Cobleskill. In Ontario count}^ at Phelps below the Oriskany 

 sandstone is found the Cobleskill or " bullhead " rock as it is 

 known in western New York. This rock here and farther west 

 at Victor and beyond, contains the Cobleskill fauna. Beneath 

 the " bullhead " rock in Ontario county in a thin bed of water- 

 lime, fragments of Eurypterus are found and at Victor a large 

 number of fragments from this horizon were obtained. Beneath 

 this layer of waterlime in Ontario county we find again in the 

 dolomite layer another Cobleskill or '' bullhead " fauna in which 

 Lie has ptyonurus Hall is found and Cyathophyllum 

 hydraulicum Simpson is quite abundant. Beneath this second 

 dolomite layer containing Cobleskill fossils, waterlime beds again 

 occur in which Eurypterus are found. 



From the above conditions it would appear that while the 

 Decker Ferry fauna was living in eastern New York the Euryp- 

 terus fauna was still to be found in the Salina sea in the western 

 part of the State, and that there were invasions from the eastern 

 sea which at first were only temporary, but which finally caused 

 the retreat or destruction of the Eurypterus fauna. 



'Geol. Soc. Am. Bui. 1900. 11:363. 



