GENERAL OBSERVATIONS. 381 



Hamilton, Marcellm (?) 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" thiek-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 brecciated and concretionary, 250 feet or more. 

 Trenton, Chazy 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. 



Corniperous, 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. 



