GEOLOGICAL STRUCTURE OF EASTERN WISCONSIN. 



247 



GEOLOGICAL STRUCTURE OF EASTERN WISCONSIN. 



The rocks of the district under consideration consist of two great 

 classes, widely distinguished in age and character. The more ancient 

 one consisted originally of sedimentary materials which were subse- 

 quently metamorphosed into quartzites, granites, porphyries and sim- 

 ilar rocks, and were folded and tilted at various angles. These (for- 

 merly known as Azoic or Eozoic) constitute the Archaean 'formations. 

 Upon these were afterwards deposited a series of sandstones, shales 

 and limestones that have remained essentially unaltered and undis- 

 turbed to the present day, which constitute the Paleozoic formations. 



The following table exhibits in their natural order the formations 

 that will claim our attention: 



HAMILTON, 



LOW T ER HELDERBERG, 



NIAGARA, - 



CINCINNATI, - 

 GALENA, - 

 TREXTON, 

 ST. PETERS, 

 LOW T ER MAGNESIAN, 

 POTSDAM, - 



HUKONIAN, - 

 LATJRENTIAN, 



Devonian, 

 [ Upper Silurian, 



. Lower Silurian, 



Archcean. 



ES 



- 

 O 

 i i 

 O 



