Periods 



SUBDIVISIONS IN THE HISTORY. 

 Fig. 134. 



131 



Epochs. 



Permian. 



Azoic. 



Upper Coal Measures. 



Lower Coal Measures. 



Millstone Grit. 



Upper. 



Lower. 



Chemung. 



Portage. 



Genesee. 



Hamilton. 



Marcellus. 



Upper Helderberg. 

 Schoharie. 

 Cauda-Galli. 

 Oriskany. 



Lower Helderberg. 



Saliferous. 



Niagara. 



Clinton. 



Medina. 

 5a Oneida. 

 4b Hudson River. 



Utica. 



f Trenton. 

 Black River. 

 Birdseye. 



Chazy. 



Calciferous. 



Potsdam. 



Azoic. 



