286 



HISTORICAL GEOLOGY 



posits. Oligocene strata have not been recognized north of South 

 Carolina. 



The Miocene beds are well developed, with a maximum thick- 

 ness of nearly 500 feet. They are made up mostly of sands, clays, 

 and marls. 



The Pliocene is represented by the marine Waccamaw forma- 

 tion, which consists mostly of buff sands with some quartz pebbles 



Fig. 177 

 Eocene sandstone resting by sharp contact upon Upper Cretaceous white 

 chalk in Alabama. (After L. W. Stephenson, U. S. Geological Survey, 

 Prof. Paper 90- J.) 



and shell marls. The Pliocene is also thought to be represented 

 by the problematical Lafayette formation (see below) , which com- 

 prises sands, clays, loams, and gravels often rich in iron oxides. 

 Its thickness seldom exceeds 50 feet. Lack of fossils makes it 

 uncertain whether the formation is late Pliocene or early Pleisto- 

 cene in age. 



Gulf Coastal Plain Strata. — Here the Lower Tertiary (Eocene 

 and Oligocene) strata are much more extensive at the surface 

 than the Upper Tertiary. Both marine and non-marine deposits 

 are present, with the former predominant. 



