39 



FOURTH REPORT — 1834. 



Periods. 



Character of Formations. 



Localities of the Formations. 



Eocene. 



A series of whitish and lead- 

 coloured friable limestones, 

 and ferruginous and siliceous 

 sands, all abounding in ex- 

 tinct species of shells and 

 zoophytes. 



Occurs also very frequently in 

 the form of a fine-grained 

 siliceous rock, abounding in 

 casts and impressions of 

 shells. This is used as a burr 

 stone in Georgia. 



Piscataway, near the Potomac 

 River, Maryland; < Upper 

 Marlboro', Maryland; Vance's 

 Ferry, South Carolina; and 

 across to Three Runs, on Sa- 

 vanna River; Shell Bluff, 

 Savanna River ; Silver Bluff 

 on the same, inBurkisCounty, 

 Georgia ; near Milledgeville 

 in Georgia ; Early County, 

 Georgia ; Wilcox County, 

 Alabama; Clayborne, Ala- 

 bama ; St. Stephens, Alaba- 

 ma ; Munroe, on the Washi- 

 taw River, west of the Mis- 

 sissippi. All these localities 

 are on the authority of Mr. 

 Conrad, who has either seen 

 them in person or received 

 eocene fossils from them. 



It is necessary, perhaps, that T here explain in what sense I 

 employ the very useful nomenclature of Lyell. I wish it to be 

 understood that I apply the terms Pleiocene, Meiocene, and Eo- 

 cene to our beds, not under the idea of any strict identity, either 

 in geological character or age, being discoverable between them 

 and the strata which have severally received those names in 

 Europe, but to express simply their own comparative chrono- 

 logical relations, and their connexion with the recent organic 

 races of this country, independently of any direct comparison 

 with formations elsewhere. It is possible, indeed it is very 

 likely, that some of our formations, our newer pleiocene, for ex- 

 ample, may exhibit in their organic remains nearly the same 

 proportion of recent species as certain beds in Europe, and yet 

 differ materially from the latter in positive age ; for I conceive 

 it is a fair inference, that throughout a certain period of more or 

 less duration, the relations of species, from general physical 

 causes, must be more stable in some regions than in others, va- 

 rying less rapidlj'^, for instance, upon the tranquil shores of the 

 United States, than near the often agitated coasts of volcanic 

 Sicily. If this view be granted, and I think it should not be 

 overlooked in attempting to establish identity of period in di- 

 stant strata, the tertiary formations of America will furnish an 

 instance in illustration of the importance of the caution recently 

 given us by Mr. Murchison and other eminent geologists of 

 England, that we make out a classification of our rocks from 

 their own relations, instead of ranking them, as we have hi- 

 therto invariably done, merely as members of European types. 



