460 



GEOLOGY OF CENTRAL WISCONSIN. 



QuATERNAET. 



Recent — Peat beds; bog iron ores. 



Champlain — Lacustrine clays, over 200 feet tliick. 



Glacial — " Drift"; including bowlders, tiU, sand, gravel, etc. 



Lower 

 Silurian. 



Trenton. 



Canadian. 



AnCHMAN. 



Huronian. 



Laurentian. 



Primordial. ' 



Galena limestone; dolomite, 300 to 350 feet. 

 Trenton limestone; alternating limestones and 

 dolomites; in all 100 to 120 feet. 



St. Peters sandstone; 15 to 120 feet. 

 Lower Magnesian limestone; dolomite, 50 to 

 125 feet. 



Madison sandstone beds, 35 

 Beds of pas- j to 50 feet. 



Mendota limestone beds, 30 

 to 45 feet. 



Including possibly two dis- 

 tinct formations, the one 

 Ij'ing upon the eroded sur- 

 Lower or Pots- I face of the other; in all 800 

 dam sandstone. ' to 1000 feet thick, but vary- 

 ing much on account of the 

 irregular surface of the un- 

 derlying rocks. 



Quartzites, schists, quartz-porphyries, silicious 



iron ores, gneiss (?); many thousand feet 



thick. 

 Gneiss, granite, scliist, diorite, quartzite, etc.; 



no crystalline hmestone; many thousand feet 



thick. 



