34 



A NATURALIST IN THE GREAT LAKES REGION 



Lower Silurian (Oswegan) 



Brassfield sandstone 



Medina sandstone 



Edge wood limestone 



Tuscarora 



Cataract sandstone or shale 



Becksie limestone 



Ordovician period 



Upper Ordovician (Cincin- 

 natian) 

 Garoche 

 Richmond limestone 



Mayville or Loraine 

 Eder or Utica shale 



Middle Ordovician (Cham- 

 plainian) 

 Collingwood limestone 

 Trenton limestone 

 Black River dolomite 

 Lowville limestone 

 Chazy limestone 

 Stones River limestone 

 St. Peter sandstone 



Lower Ordovician (Canadian) 

 Fort Cassin dolomite 

 Beekmantown or Prairie 



du Chien dolomite 

 Oneota limestone 

 Madison sandstone 

 Mendota limestone 

 The last three are possibly 

 to be put in a separate 

 period, the Ozarkian 



Cambrian period 



Upper Cambrian (Croixian) 



mostly limestones 

 Middle Cambrian (Acadian) 



mostly limestones 

 Lower Cambrian (Wauco- 

 bian) 



Girardeau 



Richmond shale and shaly limestone 

 (Maquoketa) 



Kimmeswick and Platten 

 Galena limestone 

 Platteville limestone 



St. Peter sandstone 



Shakopee dolomite, cement rock, and 



sandstone 

 New Richmond sandstone 

 Oneota dolomite 

 Jordan and Madison sandstone 

 St. Lawrence dolomite 



Franconia glauconitic sandstone 

 Potsdam (Lake Superior sandstone) 



Dresbach shale and sandstone 

 Lowest sandstone 



