DEVONIAN. 



K 17-18. NEW YORK. 



297 



According to the nomenclature of the present New York State Survey, the 

 classification of the Devonian of that State is as follows : ^"^ 



Summary of classification of the New Yorlc Devonic. 



[According to John JI. Clarke. Descending order.] 



These formations vary greatly in thickness from east to w^st and north to 

 south. The Helderbergian strata do not occur in the western part of the State. 

 The Oriskany sandstone overlaps westward into Ontario; but the Schoharie and 

 Esopus are of local distribution only. The Onondaga limestone and the Hamilton 

 and Marcellus shales are relatively widespread, as is the Genesee, or its equivalent; 

 but the Tully and Portage are more restricted. The Chemung and particularly the 

 Catskill are very thick near-shore and the latter in part continental deposits of the 

 Bay of New York and its southern extension into Virginia, and they are represented 

 farther west by the Upper Devonian shales. 



Hall ^^^ described the "Lower Helderberg" as follows: 



The Lower Helderberg group, which constitutes the more important portion of the strata 

 from which are derived the fossils of the present volume, has been so termed from its very 

 complete development along the base of the Helderberg ^Mountains, constituting, in this part 

 of New York, an important fossiliferous group. In some parts of the Helderberg Mountains 



