1156 



NEW YORK STATE MUSEUM 



Guelph element in the fauna of the Cobleskill limestone 



Mingled with the species of the Cobleskill derived from Atlantic 

 waters, there are found in Schoharie county and westward a 

 number of gastropods and cephalopods with some lamellibranchs, 

 all of which in the eastern extension of the Cobleskill are con- 

 spicuously lacking. An analysis of this element in the Cobleskill 

 fauna shows that a number of the species are identical with 

 Guelph species of New York and the West. Among these forms 

 are found such Guelph species as Orthoceras trusitum 

 Clarke & Ruedemann, Kionoceras darwini Billings and 

 1 1 i o n i a g a 1 1 e n s i s Whiteaves and other species which 

 appear in the foregoing lists. Species common to the Niagara 

 and the Guelph and not observed in the Cobleskill of eastern 

 New York occur in Schoharie county with the true Guelph 

 species. There are also Niagara species in the Cobleskill found 

 in the Niagara of the West, but which do not occur in the Niagara 

 of New York. 



The presence of Guelph species in the Cobleskill is accounted 

 for as follows. At the close of the Niagara age there was an 

 increase in the salinity of the water, which was the first step 

 toward bringing about the conditions of the Salina sea. During 

 this period following the Niagara, the Guelph fauna of New 

 York flourished, but finally retreated as the sea became more 

 saline. Again at the close of the Salina age, when in western 

 and central New l r ork nearly normal marine conditions had been 

 established, the Guelph fauna returned and met the invading 

 fauna of the Atlantic. The mingling of these two faunas shows 

 that during Cobleskill time the waters of the Atlantic and the 

 Mississippian sea were in communication. 



In the conclusion which I have reached relative to the mingling 

 of these waters I differ from Ulrich & Schuchert, 1 who state that, 

 though the barrier to the east was crossed, a younger fold " still 

 prevented the Atlantic from joining the Mississippian sea 

 throughout the time from Medina well into the Oriskany." 



1 N. Y. State Paleontologist, An. Rep't 1001. 1902. p.662. 



