On American Geological History, 411 



I— SILURFAIf AGE. 



1. Loiuer Sihirian. 



1. Potsdam Period.— 1st Epoch. Potsdam sandstone : 2nd. Calciferous 

 sandrock. 



2. Trenton Period.— 1st Epoch. Chazy limestone; 2nd. Birdseye •, 

 3rd. Black River ; 4th. Trenton. 



3. Hudson PEaioo.— 1st. Epoch. Utica Shale; 2nd. Hudfon River 

 Shale. (Hudson River Shale and Blue limestone of Ohio in parts of the 

 west.) 



2. Upper Silurian. 



1. Niagara Period.— 1st. Epoch. Oneida Conglomerate ; 2nd. Medina 

 Sandstone ; 3rd. Clinton Group ; 4th. Niagara Group. 



2. Onondaga Period.— 1st. Epoch. Gait limestone; 2nd. Onondaga 

 Salt Group. 



3. Lower Helderberg Period. — Limestones. (Statement of epochs 

 here omitted.) 



IL DEVONIAN AGE. 



1. Oriskany Period. — 1st Epoch. Oriskany Sandstone; 2nd. Canda- 

 galli Grit. 



2. Upper Helderberg Period. — 1st Epoch. [Schoharie Grit; 2nd:. 

 Upper Helderberg group. 



3. Hamilton Period. — 1st Epoch. Mareellus Shales; 2nd. Hamilton 

 group; 3rd. Genesee Slate. 



4. Chemung Period.— 1st Epoch. Portage; 2nd. Chemung group. 



5. Catskill Period. — Catskill Red Sandstones and Shales. (No. IX. of 

 Rogers.) 



IIL CARBONIFEROUS AGE. 



1. Subcarboniferous Period.— 1st Epoch. Conglomerates, Sandstone* 

 and Shales (with some coal seams ;) 2nd. Sandstones, Shales and Carboni- 

 ferous limestone. Nos. X. and XL of Rogers. 



2. Carboniferous Period.— 1st Epoch. Millstone Grit ; 2nd. Lower Coal 

 Measures ; 3rd. Upper Coal Measures. Nos. XIL and XIII. of Rogers. 



8. Permian Period — Probably unrepresented in Eastern North America^ 

 except by the events of the Appalachian Revolution. 



Before continuing tlie review, I will mention some conclusions 

 which are here suo-o-ested. 



I. In the first place, through the periods of the Silurian and 

 Devonian, at twelve distinct epochs at least, the seas over this 

 American continent were swept of all or nearly all existing life, 

 and as many times they were repeopled : and this is independent 

 of many partial exterminations and renewals of life that at other 

 times occurred. 



If Omnipotent Power had been limited to making monads for 

 after development into higher forms, many a time would the 



