ORISKANiAN FAtJNA 29l 



Helclerbergian. In thickness it is not less than 800 feet, and as a few of 

 the typical Oriskany species continue into the sandstones above, prove 

 that some of this depth is to be included with the Oriskany or with the 

 Esopus grit, of which fauna in the typical area, New York, practically 

 nothing is known. 



The detailed distribution, lithologi'c character, thickness, and local 

 faunae are given in full further on (see pages 300-331). 



Oriskanian fauna.— As a rule the Oriskany formation consists of littoral 

 deposits, often of a very coarse nature. When it is remembered that, in 

 addition to this fact, the formation has very limited, usually linear ex- 

 posures, it is remarkable that its fauna should consist of 185 species. 

 Chief among these are the brachiopods, of which 97 species are known. 

 They are the most abundant fossils, and their generally larger growth 

 at once marks the Oriskany as one of the easily recognized American 

 Paleozoic faunas. 



In spite of the characteristic expression of the Oriskany fauna, it is 

 remarkable that it should be so intimately connected both with the 

 Helderbergian and with the Onondaga. Its affinities with the former 

 are, of course, due to the recent discovery of a lower Oriskany fauna. 

 Of the 185 species included in the Oriskany fauna, 31, or 17 per cent, 

 come from the Helderbergian, while 54, or 35 per cent, pass into the 

 Onondaga. Of the Helderbergian species, 24 pass into the Lower 

 Oriskany, 17 into the Upper Oriskany, and 5 through both into the 

 Onondaga. The last are Favosites conicus, F. gotlandicus, Leptasna rhom- 

 boidalis, Atrypa reticularis, and Dalmanites pleuroptyx. The Lower and 

 Upper Oriskany zones have 43 species in common, or a little more than 

 23 per cent. These figures prove that the Oriskany is intimately con- 

 nected with the Helderbergian and Onondaga. This is still more forci- 

 bly brought out when it is stated that of the Becraft fauna, the one im- 

 mediately beneath the Oriskan}^, not less than 27 per cent of its species 

 pass into the Oriskany.* All these figures are in strong contrast with 

 the very few species which pass from the Niagaran and Cayugan forma- 

 tions into the Helderbergian. Of these there are 9 persisting forms, or 

 about 2 per cent, in a fauna of 459 described species. 



The Lower Oriskany of New York, Illinois, and Tennessee, probably 

 represents a fauna practically of one zone. The Upper Oriskany, how- 

 ever, seems to have three overlapping stages. The New York Hippa- 

 rionyx fauna apparent^ holds a central position ; that of Cumberland 



* Doctor John M. Clarke writes that the lowest Lower Oriskany beds of Becraft mountain have 

 "a recurrent shaly limestone fauna," after which the true Lower Oriskany fauna makes its ap- 

 pearance. It is therefore probable that the percentage here given will be reduced, since the list 

 beyond includes these beds in the Lower Oriskany. 



