GEOLOGICAL STRUCTURE OF EASTERN WISCONSIN. 



24:t 



GEOLOGICAL STRUCTUEE OF EASTERN WISCONSIl^. 



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: 



Hamii-ton, 



LowEE Heldeebeeg, 



NiAGAEA, 



Cincinnati, 

 Galena, 

 Teenton, 

 St. Petees, 

 LowEB Magnesian, 

 Potsdam, 

 hueonian, - 

 Laueentian, 



Devonian, 

 ITpper Silu7'ian, 



L Lower Silurian, 



Archoecm. 



o 

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