THE WORLD IN THE MAKING 35 



pROTEROzoic Era 



The chief rock systems in this era in the Great Lakes region are in 

 northern Michigan, Wisconsin, and Minnesota. In northern Michigan 

 they are as follows: 



Upper Ke ween a wan 

 Freda sandstone 

 Nonesuch shale 

 Outer conglomerate 



Lower Keweenawan 

 . Lake shore trap (basic lava) 

 Great conglomerate 

 Eagle River and Ashbed 



group (acid lava intru- 



sives) 

 Mesnard epidote 

 Central mine group (basic 



lavas) 

 Conglomerate (acid lava 



intrusives) 

 Bohemia Range (mostly 



basic lavas) 



Upper Huronian 



Clarksburg formation 



Michigamme slate anri 

 schist 



Goodrich formation (mostly 

 quartzite and conglom- 

 erate) 



Middle Huronian 

 Presque Isle granite 

 Quinnisec schist 

 Tyler and Hanbury forma- 

 tions 

 Negaunee, Vulcan, and 



Ironwood formations 

 Ajibik, Siamo, and Palms 



formations 

 Hemlock formation (basic 



lavas) 

 Kona, Randville, and Bad 



River formations 

 Mesnard, Sturgeon, and 



Sunday formations 



(mostly quartzite) 



Archaeozoic Era 

 Laurentian 

 Keewatin 



