84 NEAY YORK STATE MUSEUM 



fauna! traits of the Helderbergian, with the exception of Charles 

 Schuchert, of Washington, who, after expressing his conviction of their 

 Devonic character, resulting from protracted study of the brachiopods 

 of the fauna 1 has entered into the subject in much detail and with 

 great force. 2 George H. Girty has discussed the characters of the 

 sponges and coelentrates of this fauna in a valuable paper published 

 in the Uih ann mil report of the New York state geologist, 1805, but 

 without entering widely into the consideration of the faunal bearing of 

 the species discussed. For the rest, stratigraphers, cartographers, writers 

 of textbooks and others who have had no occasion to consider the subject 

 on its merits and perhaps no adecpiate appreciation of the merits of 

 the question, have till lately been content still to accept the view 

 promulgated largely by the influence of Murchison, that the fauna 

 constitutes a terminal member of the upper Siluric section in New York. 

 No full analysis of the constituents of the typical Helderbergian 

 fauna can be presented here, nor is it essential. A review of the 

 species of the entire fauna with the incorporation of the very consid- 

 erable number of undescribed forms known to occur in it would be 

 necessary to set the matter forth with its full force. It will suffice 

 here to restate briefly the leading features of the association which must 

 be relied on to determine its age. Let this statement, however, pre- 

 face the present discussion. J he Helderbergian fauna is that contained 

 by tin strata, all ami several, lying betiveen the top of the Tentaculite 

 (M<i n1 ins) Umt stone below, and the top of the Kingston beds above. 



The Helderbergian fauna 



Siluric characters 



Positive elements 



IrUobites. There are no features presented by the trilobites which 

 indicate Siluric age. 



Cephalqpods. In the Helderbergian, representatives of the cephalo- 

 pods are most rare. The species of the genera Orthoceras, and 



1 See Bull. U.S. geol. sur. 1897. no. 87. 



2 Bull. geol. soc. America 1900. 11 : 241-332. 



