Page:The Eurypterida of New York Volume 1.pdf/110

 deposits of the Salina formation and the absence of fossils in the middle Salina beds (Vernon, Camillus shale) which were early ascribed to "salt pan" conditions in the Salina sea. The authors have pointed out in Memoir 5 [Guelph Fauna of New York, p. 117] that the preceding Guelph was a distinct phase in the development of the vast Niagara coral sea into the desiccating, more or less inclosed sea of the Salina stage, the fauna of the Guelph already exhibiting characters suggestive of the increased salinity of the sea. The cycle of events leading to the culmination and decline of the Salina sea has been expressed by Hartnagel in the appended diagram and described as follows:

With the ever increasing salinity of the waters the Guelph fauna retreats, and next in the black Pittsford shale at the base of the Salina there occur Eurypteri, and with them constantly associated a species of Lingula. With the retreat of this fauna we find, as physical changes went on, deposits of gypseous shale and later the salt beds. The deposition of these great beds of rock salt marks the turning point in this cycle,. . . beds of gypsum were again deposited, but never again were the conditions favorable for the deposition of extensive beds of rock salt. Following the gypsum beds, we have the Salina waterlime with its splendid Eurypterus fauna, and associated with the Eurypterus is a species of Lingula