490 



CENOZOIC TIME. 





3. Pliocene, from irXumv, more, etc. ; more than half the species 

 living. 



Some European geologists make a fourth division, called Oliyocene, by separating an 

 upper portion of the Eocene, and uniting with it the lower section of the Miocene; and 

 a fifth, Puleocene, by so naming the lower division of the Eocene. 



1. American. 



The periods recognized are, if the Laramie group is included : — 



1. The Laramie or Lignitic period, represented partly by brackish- 

 water beds, which in general are unconformable to the overlying Ter- 

 tiary. • After this — 



A. On the Eastern Border, where the beds are marine. 



2. The Alabama period, corresponding to the Eocene, and includ- 

 ing (1) the Claiborne group, and (2) the Vicksburg group, which occur 

 along the Gulf and Atlantic border. 



3. The Yorktown period (named from Yorktown, Va.), which cov- 

 ers the Miocene, and possibly part of the Pliocene, and whose beds are 

 found on the Atlantic border, from South Carolina to New England, 

 and farther north off the coast, but not on the Gulf border. 



4. The Sumter epoch (named from a locality in South Carolina), 

 corresponding to the Pliocene, or part of it. 



B. Over the Rocky Mountain slopes and west of the summit, where 

 the beds are of fresh-water origin. 



2. The Eocene is made to include the following groups, commen- 

 cing below: (1) The Wahsatch (named from the Wahsatch Mountains); 

 (2) the Green River, or the lower fish-bearing shales of the Green 

 River Basin, perhaps cotemporaneous with the Wahsatch; (3) the 

 Bridger (named from Fort Bridger), including the upper beds of the 

 Green River Basin, etc., and containing bones of Mammals ; (4) the 

 Uinta (named from the Uinta Mountains). 



3. The Miocene, includes the White River group, a part of the 

 Upper Missouri region, where the beds have a wide extent. 



4. The Pliocene includes the Niobrara group (named from a 

 branch of the Missouri River), and other groups. 



1. Rocks: kinds and distribution. 



The deposits are either of marine or of fresh-water origin. The 

 marine serve to mark out approximately the limits of the oceans over 

 the continents, while the fresh-water are mostly of lacustrine origin. 



The Tertiary areas on the map, p. 144, are lined obliquely from the left above to the 

 right below; and the fresh and brackish- water Tertiary area, which occurs on the slopes 

 of the Rocky Mountains, is distinguished from the marine by a more open lining. 



The marine Tertiary beds occur on the Atlantic Border, in deep 

 water along the banks off the coast of northern New England; on 



