GENERAL OBSERVATIONS. 381 



Hamilton, Marcellus (?) Epoch. — Black, bituminous limestone, 15 feet. 



Hamilton Epoch. — Argillaceous limestones, 17 feet; crystalline lime- 

 stone with included lenticular clayey masses, 23 feet : total, 40 feet. 

 Contains a bed of coal on Little Traverse Bay. 

 Genesee (?) Epoch. — Black, bituminous shale, 20 feet, 

 Chemung, Portage Epoch. — " Huron" shales with intercalated flagstones and 

 limestones, 190 feet. 



Carboniferous. 



Subcarboniferous, Lower. — " Huron" and "Marshall" (= Chemung?) grit- 

 stones, and reddish, yellowish, and greenish sandstones and conglome- 

 rates, 173 feet ; " Napoleon sandstone," generally micaceous, with 

 clay beneath, 123 feet; "Michigan Salt-group," carbonaceous and 

 argillaceous shales, magnesian and arenaceous limestones, and thick 

 beds of gypsum, 184 feet : total, 480 feet. 

 Upper. — Limestones, arenaceous below, 66 feet. 



Carboniferous, Millstone- Grit Epoch. — "Parma" thick-bedded sandstone, in 

 some places conglomeritic, 105 feet. 

 Coal Measures. — Bituminous shales, and fire-clays, with occasional thin 

 sandstones and limestones, 123 feet ; " Woodville" sandstone, 79 feet ; 

 total, 202 feet. 



3. Iowa Section. 

 Lower Silurian. 



Potsdam, Potsdam Epoch. — Very pure sandstone, with some thin, calcareous, 



shaly layers, 500 feet. 

 Calciferous Epoch. — " Magnesian" limestone, almost chemically pure, 



sometimes breeciated and concretionary, 250 feet or more. 

 Trenton, Ohazy Epoch. — " St. Peter's Sandstone," a granular, rarely compact 



sandrock, 80 feet. 

 Trenton Epoch. — " Buff," " Blue" and " Galena" magnesian limestones, 



with some shaly portions in the lower layers, 350 feet. 

 Hudson, Hudson Epoch. — Siliceous and argillaceous shales, mostly bituminous, 



80-100 feet. 



Upper Silurian. 



Niagara, Clinton and Niagara Epochs. — Light yellowish-gray compact magne- 

 sian limestone, with much chert, 150-300 feet. 



Salina, Leclaire Epoch. — Gray semi-crystalline porous limestone, 600-700 feet. 

 Saliferous Epoch. — Thin-bedded, drab-colored limestones, with shaly 

 partings, 100-150 feet. 



Devonian. 



Corniferous, Upper Helderberg Epoch (?).— Gray compact limestone, with 

 some concretionary and shaly layers, 50 feet or more. 



Hamilton, Hamilton Epoch (?).— Magnesian limestones, 100 feet. 



Chemung, Chemung Epoch.— [Subcarboniferous in part?] Siliceous shales, some- 

 times calcareous, 100 feet or more. 



