THE TERTIARY PERIOD 



285 



Atlantic Coastal Plain. All the formations, except possibly the 

 Lafayette, are there of marine origin and usually very fossiliferous. 



Fig. 176 

 Map showing the surface distribution (areas of outcrops) of Upper Tertiary 

 (Miocene and Pliocene) strata in North America. (Modified by W. J. M. 

 after Willis, U. S. Geological Survey.) 



The Eocene formations consist very largely of greensand marls 

 and some clays. They show a maximum thickness of about 250 

 feet in Maryland and rest unconformably upon the older de- 



