56 



NEW YORK STATE MUSEUM 



6 Arenaceous shale with Homalonotus dekayi, Or- 

 thonota, abounding in grotesque calcareous concretions and 

 passing into a thin limestone above, 12 feet 



7 Olive shale 



8 Very soft light gray shales with Ambocoelia, Chonetes, 

 Athyris and Phacops in distant thin layers 



9 Olive shale 

 Tully pyrite 

 Genesee shale 



Tully limestone and pyrite 



What little Tully limestone is here represented carries the 

 indicial species Hypothyris cuboides Sowerby (sp.) 

 identified originally by Conrad with Sowerby's Rhyncho- 

 nella cuboides and subsequently described by Hall as 

 R. v e n u s t u 1 a. 



The species R. cuboides was long ago referred by King 

 to the genus Hypothyris. This world-wide species is here a 

 newcomer into the Devonic faunas and is associated through- 

 out the exposures of the Tully with an assemblage essentially 

 consisting of Hamilton species, though slight variations from 

 Hamilton types are indicated and there are a few additional 

 species present like the very characteristic trilobite B r o n - 

 teus tullius Hall & Clarke. For at least a half century 

 Hypothyris cuboides has been recognized as indicative 

 of lowest upper Devonic age and the Bronteus associated with 

 it is likewise of early Devonic type (Tkysanopeltis) . The fact 

 that these species accompany an essentially unmodified fauna 

 of earlier age does not argue that age for the limestone but 

 serves to emphasize if anything the introduction of new types 

 indicative of fundamental change. 



The fauna of the pyrite layer is a parvifauna with affinities 

 wholly or essentially with that of the Hamilton shales. It is 

 in fact a series of forms which have as a whole suffered an 

 arrest of development, and its species are immature stages of 

 those preceding though they are actually in adult condition. 

 The conditions of growth while this pyrite was being precipi- 



