PALEONTOLOGY OF IE¥-YORK. 



ROCKS OF THE HELDERBERG MOUNTAINS. 



LowEB Helderbekq Group 



A SECTION of the strata, comprising the Helderberg mountains proper in 

 Albany county, and the same in Schoharie and the adjoining counties, 

 presents the following groups and beds in the descending order : 



Hamilton group. 



iCorniferous limestone. 

 Onondaga limestone. 

 Schoharie grit. 

 Cauda-galli grit. 

 Oriskany sandstone. 

 ' Upper Pentamerus limestone. 

 Encrinal limestone. 

 Delthyris shaly limestone. 

 Pentamerus limestone. 

 , Tentaculite or Water limestone. 

 Argillaceous and Magnesian limestones of the "\ 

 Onondaga-salt group. I 



Coralline or Niagara limestone*. ) 



The fossils described in the present voliftne are from the limestones 

 constituting the Lower Helderberg group, and from the Oriskany sand- 

 stone. Although convenient for local reference, I have found it impossible 

 to recognize the subdivisions, instituted in the Geological Reports, at 

 any great distance from the Helderberg mountains ; while the group, as a 

 whole, has a wide geographical distribution from northeast to southwest, 

 characterized by numerous fossils. 



• Those beds together are rarely more, than twenty-flTe feet in thickness, and produce no conspicuous 

 feature in the geology or topography of this region. 

 [ PALiKONTOLOGT III.] 18 



