138 NEW YORK STATE MUSEUM 



part of the interior sea most favorable for its increase. Here it 

 is followed and preceded by a quite distinct association involved 

 in bituminous muds, and it is therefore natural that a few of the 

 Marcellus si)ecies have sti-ayed into the Agoniatite fauna. The 

 tendency to lime dei>osition recurred during Marcellus time after 

 the sea had shallowed in western New York, but ere that event 

 the Agoniatite derivative of the Onondaga fauna had migrated 

 eastward and disapi>eared. 



The fauna of the Stafford limestone was also an itivader of later 

 date from the west and tJie second apiwarance of tJw Hamilton fauna 

 within the confines of this state. 



The composition of the species list is final in detennining the 

 affiliation of the Statford fauna. This invasion, too, was unsuc- 

 cessful, reaching no farther eastward than the eastern part of 

 Ontario county. Had the fauna dispersed more widely and been 

 able to take and keep possession of the ground which it subse- 

 quently acquired, Hamilton time and sedimentation would have 

 been a more important element in the Kew York succession. 



