956 A. W. GEABAU THE TULLY LIMESTONE 



of Ulster Caunty^ though good bluestone is also found in the overlying 

 Oneonta. Tully and Genesee sedimentation are entirely wanting in the 

 eastern basin^ both the sediments and the faunas being kept out by the 

 Sherburne bar. 



The north-south section (figure 2, page 950), together with the east- 

 west section (figure 1, page 950), will make clear the conditions of things 

 which existed in Upper Devonic time in the eastern section of North 

 America, and the map (figure 3) is an attempt at depicting the physiog- 

 raphy of North America in Tully time. 



The Tully Fauna 



The fauna of the Tully limestone of New York is a composite one, con- 

 sisting in part of (1) unmodified or persistent Hamilton species, in part 

 of (2) species of the Hamilton fauna modified in situ, and in part of (3) 

 immigrant species. Of the first group (1) we may mention: 



1. Amhocoelid umbonata. 



2. Atrypa reticularis. 



3. Atrypa spinosa. 



4. Cyrtina hamiltonensis. 



5. Schuchertella arctostriata. 



6. Spirifer fimbriatus. 



7. Spirifer tullius. 



8. Cryphceus hoothi. 



9. Phacops hufo. 



and species of Hamilton gastropods, pelecypods, cephalopods, and corals. 



(2) Species modified apparently in this region from the Hamilton 

 fauna, which was cut off from its source of supply by the development of 

 the Sherburne bar, comprise the following significant forms : 



1. Chonetes aurora Hall. 



This is known only from this horizon and has not been found outside 

 of the State. It is probably a Hamilton derivative. 



2. Productella spinulicosta var. tuUiensis H. S. Williams. 



A local modification of the characteristic Hamilton species. 



3. Spirifer mucronatus var. tuUiensis H. S. Williams. 



Transitional, according to Williams, from the Hamilton form to the 

 S. rnesicosfalis, prol)ably through S. mucronatus var. posterus. 



