SUBDIVISIONS IN THE HISTORY. 



131 



Periods. 



Fisr. 134. 



Epochs. 



Permian. 



Upper Coal Measures. 



Lower Coal Measures. 



Upper Helderberg. 

 Schoharie. 

 Cauda-Galli. 

 Oriskany. 



Lower Helderberg. 



Azoic. 



Utica. 



[ Trenton. 



Black River. 



Birdseye. 

 Chazy. 

 Calciferous. 

 Potsdam. 



Azoic. 



