THE DWARF FAUNA OF THE PYRITE LAYER AT THE 

 HORIZON OF THE TULLY LIMESTONE IN WESTERN 



NEW YORK 



BY P. B. LOOMIS 



Plates 1-5 



Recent determinations by the state paleontologist have shown 

 that the Tully limestone which in central New York caps the 

 Hamilton shales in its westward extension, feathers close to 

 the east shore of Canandaigua lake, and from there westward 

 to Lake Erie its place in the stratigraphic succession is marked 

 by a thin sheet of pyrite from 1 to 4 inches in thickness. This 

 pyrite deposit is often continuous for considerable distances, 

 appearing in the strike at certain localities without break for 

 a length of one to a few rods, and when interrupted it is only 

 for a short interval. It may be looked on as an essentially 

 continuous mantle, always maintaining its stratigraphic posi- 

 tion between the calcareous Hamilton and the bituminous Gen- 

 esee shales. It is a deposition synchronous with and in continu- 

 ation of the Tully limestone in a region where that formation is 

 no longer represented by limestone sedimentation, where indeed 

 bathymetric conditions did not permit the deposition of such a 

 sediment. The highly bituminous deposits of the Genesee sea 

 indicate befouled waters where organic decomposition was ex- 

 tensively under way. The inception of these conditions is strongly 

 expressed by the presence of the pyrite sheet 100 miles in extent 

 on the strike; and in fact a similar indication is presented by 

 the Tully limestone itself, which for some extent along its feather- 

 ing edge carries considerable quantities of pyrite. 



The fauna of the Tully limestone is essentially a congeries 

 of Hamilton species, but, added thereto, it contains the well 

 known and far scattered brachiopod Hypothyris cuboides 

 Sowerby, which has been called by Hall Rhynchonella 

 venustula. For more than 50 years this species has 'been 

 recognized as an index of early Upper Devonic time, and this 

 diagnosis of its time value is supplemented by certain estab- 

 lished mutations of earlier species. The Tully limestone thus 

 represents the opening stage of Upper Devonic time in the New 

 York succession. 



