14 HARPER 



belts approximately parallel to the coast, as indicated on the map 

 (See frontispiece). 



South Georgia contains the following well-marked natural 

 subdivisions. 



i. Fall-line sand-hills. Extending with some interruptions 

 along the fall-line, not only in Georgia 1 but in the Carolinas 2 and 

 apparently also in Alabama, 3 is a rather narrow belt of sand- 

 hills, standing higher than the rest of the coastal plain on one 

 side and the Piedmont region on the other. (Between the Flint 

 and Chattahoochee rivers the summits of the fall-line sand-hills 

 are nearly if not quite 700 feet above sea-level, being probably 

 the highest part of the coastal plain in the Eastern United States.) 

 The soil of the sand-hills is nearly pure sand, apparently of the 

 Columbia formation (though a much greater age is assigned to it 

 by some geologists) . The maximum depth of the sand is unknown, 

 but there is no reason to suppose that it constitutes the whole 

 of the hills from top to bottom. The topography of the sand- 

 hill belt was probably carved out during the Tertiary period, 

 and then during the Pleistocene submergence covered with the 

 mantle of sand which effectually protects the underlying clay or 

 rocks from erosion. It is not yet known why sand-hills of this 

 type are confined to the vicinity of the fall-line, or what relation 

 they b£ar to the Cretaceous and Eocene rocks. Their flora is very 

 similar to that of the river and creek sand-hills which will be dis- 

 cussed in some of the succeeding pages. 



2. Cretaceous. The Cretaceous is not very well represented 

 in Georgia, comprising only about 2% of the area of the coastal 

 plain. It is extensive enough to give character to the topog- 

 raphy only west of the Flint River. East of there it is found 

 outcropping in some ravines near the fall-line, but cannot very 

 well be shown on a map. 



The Cretaceous rocks in Georgia are mostly argillaceous, 

 with some traces of calcium carbonate, and have usually a 

 characteristic gray color. (The Selma Chalk or Rotten Lime- 



1 Bull. Torrey Club 31: 10-12. 1904. 

 * Torreya 3: 121. 1903. 



3 Smith, Geol. of the Coastal Plain of Ala. 349. 1894 ; Mohr, Plant 

 Life~_of'Ala. 96-97. 1901. 



