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NEW YORK STATE MUSEUM 



Not only is the continued predominance of Helderberg species in this 

 summary, combined with the first appearance of Oriskany types, confirma- 

 tory of Professor Chadwick's view that the fauna is the passing phase of 

 the Helderberg but it is in accord with our views of affiliation in the case 

 of such clearly mixed combinations to assert that the presence of the later 

 species indicating a new invasion is a proper index of Oriskany age. 



Oriskany fauna. Considering now the composition of the more normal 

 Oriskany fauna in this eastern region in the light of newer developments 

 ',we are presented with the fact that there is yet no intimate distinction in 

 t he species from the calcareous beds and those which are distinctively arena- 

 c ~ous. The limestones of this horizon are all pretty highly impregnated 

 w j t kh sand and their weathered parts always afford the best material for 

 stuc -'y e ' tner ' n tne f rm f silica replacements or sharp external and internal 

 casts i' in res 'd ua l sand. The fauna at Becraft mountain reported by Clarke 

 was oLt' >ta i ne d wholly from weathered residua of sandy limestone. The very 

 fine m el "i a l obtained at and about Glenerie occurs best as silica replace- 

 ment ^' f ten of very remarkable perfection, in pockets filled with the loose 

 sand f r tted limestone, in all respects a parallel occurrence to the fine 



