BRACHIOPODA. 



336(7 



§ 2. 

 S "^ 



w 





t-l 



o 



GC 



6 



Lower Cambrian, 



Middle Cambrian. 



Upper Cambrian. 



Calciferous. 



Cliazy. 



Trenton. 



Utica. 



Hiirlsoii Hiver. 



Clinton. 



Niagara. 



Lower lleklerberg. 



Oriskany. 



Upper Helderberg. 



Hamilton. 



Chemung. 



Waverly. 



Burlington. 



Keokuk. 



St. Louis. 



Kaskaskia, 

 Chester. 



Lr. Coal Measure.'?. 



Middle and Upper 

 Coal Measures. 



Permian. 

 Triassie, 



