668 NEiW YORK STATE MUSEUM 



bite, cephalopod and gastropod facies unequally developed 

 locally, is a complex congeries, largely from the western 

 reaches of the Appalachian gulf, but freely inoculated with 

 elements genetically from the northeast. The latter may have 

 come in directly, geographically and genetically, through the 

 Oriskany province of eastern New York or indirectly into the 

 western limestones, after migration from New York southward 

 to the end of the barrier and thence into the heart of the gulf. 

 The latter seems specially probable of the gastropod element. 



Marcellus fauna 

 As the Onondaga limestone fauna came in from the west, so 

 it withdrew westward. In the latest stages of its immigration 

 it brought in the cephalopod Agoniatites expansus; 

 but when this species had penetrated to eastern New York this 

 ground had been occupied for some time by shallowed and foul 

 waters, wherein were depositing the black muds of the Marcel- 

 lus shale with its accompanying singular fauna. Early Mar- 

 cellus deposits in eastern New York were thus contemporane- 

 ous with late Onondaga deposits in western New York. This 

 being true, the Marcellus fauna entered the New York area of 

 the gulf from the southeast or from the direction of the eastern 

 shore. The effect of the putative eastern barrier and its accom- 

 panying northeast channel is now no longer perceptible save as 

 we ascribe to the submergence of the latter in part the befoul- 

 ing of the waters. 



Fauna of the Agoniatites limestone 



It has just been stated that Agoniatites expansus 

 came into New York from the west in the closing stage of 

 Onondaga time. The limestone to which it appertains forms 

 a very distinct band in the Marcellus section of eastern and 

 central New York, and associated with it is a small and exclu- 

 sive congeries of species, with some which belong to the fauna 

 of the shales. So far as concerns the peculiar species which 

 characterize the fauna, they have probably all been derived 

 from the same direction at the same time as Agon, ex- 

 pansus. 



