576 



EOCENE AND OLIGOCENE PERIODS 



are found on the Pacific coast, but the record of the period here is 

 found chiefly in the unconformity between the Eocene and the 

 Miocene. 



Considerable geographic changes occurred during the Oligocene, 

 or at its close, especially in the Gulf and Caribbean regions, where 

 the Oligocene (early Oligocene) is commonly conformable on the 

 Eocene, and unconformable beneath the Miocene. 



Fig. 484. Oligocene Bad Lands of South Dakota. (Williston.) 



Europe. Toward the close of the Eocene, the epicontinental 

 sea of northern Europe was greatly restricted, but considerable 

 areas stood so near sea-level that slight changes served greatly to 

 diminish or extend the epicontinental waters. 



The oldest Oligocene deposits of central and western Europe 

 are largely of terrestrial, fresh- and brackish-water origin. Local 

 deposits of salt, gypsum, and coal are suggestive of the physical 

 conditions at various times and places. The Oligocene of southern 

 Europe is chiefly marine. 



In Europe, as in North America, there were considerable igneous 

 eruptions during the Tertiary, and especially during the Oligocene. 

 Between eruptions, vegetation grew in marshes and shallow lakes 



