NOTES ON THE GEOLOGY OF GEORGIA 179 



MIOCENE SERIES 



The Marks Head Marl and the Duplin marl are the only forma- 

 tions belonging to the Miocene series. These two formations, which 

 are best developed at Porters Landing on Savannah River, consist 

 mainly of marls, sands, and clays. The Marks Head marl uncon- 

 formably overlies the Alum Bluff formation. 



PLIOCENE SERIES 



The Charlton formation, which is supposed to belong to the 

 Pliocene series, occurs along St. Marys and Satilla rivers in the 

 extreme southern part of the state. The formation consists mainly 

 of shell marls. 



The Altamaha (Lafayette ?) formation, not shown in the columnar 

 section, has the greatest areal extent of any formation in the 

 Coastal Plain, covering approximately 21,000 square miles. Like 

 the underlying Charlton formation, it is supposed to be Pliocene. 

 The formation has a maximum thickness of less than three hundred 

 feet and consists chiefly of sand, gravel, and clay, which in places 

 become indurated. With the exception of a few fragments of wood 

 it is entirely free from organic remains. 



QUATERNARY SYSTEM 

 PLEISTOCENE SERIES 



The Pleistocene is represented by the Okefenokee and the 

 Satilla formations, divisions of the Columbia group. These forma- 

 tions form a belt along the Atlantic Coast, with a width from twenty 

 to fifty miles. The Okefenokee consists chiefly of gray sand, and 

 the Satilla is made up of greenish and bluish marine clays and gray 

 and yellow sands. 



