418 On American Geological History, 



inor aire, and the salt waters of the Mexican Gulf were withdrawn 

 from the region of Iowa and Wisconsin, so as not to reach beyond 

 the limits of Tennessee.'* 



Two or three times in the course of the Tertiary Period, the 

 life of the seas was exterminated, so that the fossils of the later 

 Tertiary are not identical with any in the earliest beds, — ex- 

 cluding some fish remains, species not confined to the coast 

 waters. The crust of the earth was still oscillating ; for the 

 close of the first Tertiary epoch was a time of subsidence ; but 

 the oscillation or change of level was slight, and by the end of 

 the Tertiary, the continent on the east stood within a few feet of 

 its present elevation, while the Gulf of Mexico was reduced 

 nearly to its present limits.f 



I have thus brought this rapid stetch to the close of the Ter- 

 tiary, having omitted much of great interest, in order to direct 

 attention to the one grand fact, — that the continent from the 

 Potsdam sandstone, or before, to the Upper Tertiary, was one in 

 its progress, — a single consecutive series of events according to a 

 common law. It is seen, that the great system of oscillations, 

 due to force pressing or acting from the southeast, which reached 

 its climax in the rise of the Appalachians, then commenced a 

 decline. We mark the oscillations still producing great results 



* The recent investigations of F. B. Meek and Dr. J. V. Hayden, have 

 shown (Proe. Acad. Nat. Sci. Philad., viii, 111, 1856,) that while there is 

 m.\ic\\ fresh- water tertiary in the Nebraska regions and beyond, there is also 

 about the head waters of the Missouri some marme tertiary. The region 

 invest'gated lies between the 46th and 49th parallels of North latitude and 

 the 100th and 108th degrees of longitude: but it is not yet ascertained 

 whether the body of salt water thus indicated was an isolated area, or an 

 arm from the Mexican Gulf. The shells, (species of Ostrea, Corbula, and 

 Ceiiihium) do not satisfactorily fix the age of the tertiary, but suggest, the 

 authors say, that it may be the older Eocene. They occur in the same beds 

 with numerous freshwater shells.species of Melania, Physa, Paludina,Cyrena, 

 and all are such kinds as inhabit fresh and brackish waters. The teitiary 

 deposits of the Bad Lands, or that part where the bones occur, have afforded 

 no evidence of salt water origin ; and the same is true of the Lignite beds 

 of the far north. While therefore the tertiary beds are extensive, the 

 marine tertiary, indicating the presence of the sea, as far as present know- 

 ledge goes, is quite limited. 



I Naming the North American Tertiary Epochs from prominent localities 

 as in the Palaeozoic, they are : — 1. The Claiborne, or Older Eocene ; 2. The 

 VicKSBURQ, or Newer Eocene ; 3. The Yoektown, or Pliocene and Miocene 

 in one. 



