BRA CHI OP ODA , 
336a 
3 
Lower Cambrian. 
Middle Cambrian. 
Upper Cambrian. 
Calciferous. 
Chazy. 
Trenton. 
Utica. 
Hudson River. 
Clinton. 
Niagara. 
Lower Helderberg. 
Oriskany. 
Upper Helderberg. 
Hamilton. 
Chemung. 
Waverly. 
Burlington. 
Keokuk. 
St. Louis. 
Kaskaskia, 
Chester. 
Lr. Coal Measures. 
Middle and Upper 
Coal Measures. 
Permian. 
Triassic. 
