PALEONTOLOGY OP NEW-YOEK. 
ROCKS OF THE HELDERBERG MOUNTAINS. 
A section of the strata comprising the Helclerberg 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. 
Upper Helderberg Group : 
Lower Helderberg Group : 
I" Corniferous limestone. 
^ Onondaga limestone. 
^ Schoharie grit. 
Cauda-galli grit. 
Oriskany sandstone. 
" Upper Pentamerus limestone. 
Encrinal limestone. 
Delthyris slialy limestone. 
Pentamerus limestone. 
^ Tentaculite or Water limestone. 
Argillaceous and Magnesian limestones of the ] 
Onondaga-salt group. J- 
Coralline or Niagara limestone*. J 
The fossils described in the present volume 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. 
* These beds together are rarely more than twenty-five feet in thickness, and produce no conspicuous 
feature in the geology or topography of this region. 
[ Palaeontology III.] 13 
