ALTAMAHA GRIT REGION OF GEORGIA 15 



stone, which is said to be such a notable feature of the Creta- 

 ceous region of Alabama, forming the " black prairies" there, 1 

 is not known in Georgia.) The topography suggests that of the 

 Appalachian Valley on a reduced scale, the valleys being broader 

 than the ridges, showing that the region has been exposed to 

 erosion a relatively long time. 2 The soils of this region are mostly 

 derived from the Lafayette and Columbia formations, the former 

 being often (perhaps usually) not more than ten feet in thick- 

 ness, and the latter on top of it still less, or wanting. 



3. Eocene. The Eocene region is quite extensive in Georgia, 

 reaching entirely across the state and covering about 18% of the 

 coastal plain. Geologists recognize several subdivisions, Mid- 

 way an, Chickasawan or Sabine, Claibornian, etc., but these do 

 not differ much from each other in surface features except that 

 the Sabine is usually more level than the rest, and contains a few 

 shallow ponds. 



The Eocene rocks in Georgia were probably mostly limestone 

 when first formed, but now those that crop out (except on river 

 bluffs) are usually almost completely silicified, and their hardness 

 gives rise to the most rugged topography in South Georgia. 

 There are many places in the Eocene region where the topog- 

 raphy and flora are strikingly similar to those of the Piedmont 

 region a hundred miles farther north. Probably 99% of the 

 Eocene strata are covered by the red loam of the Lafayette for- 

 mation, often of considerable thickness. The Columbia is not so 

 extensive here as in the Cretaceous region, probably because it 

 has long ago been washed off the steep hillsides, or because the 

 Eocene region stands higher and was not all submerged in the 

 Columbia epoch. 



In both the Cretaceous and Eocene regions of Georgia broad- 

 leaved forests predominate, and their aspect is quite like that of 

 the Middle Georgia forests, but they are readily distinguished 

 by the constant presence of a few species confined to the coastal 

 plain, such as Pinus glabra, Dendropogon usneoides, Uvularia 

 Floridana, Smilax pumila, Myrica cerifera, Quercus laurifolia, 



1 See Mohr, Contr. U. S. Nat. Herb. 6: 97-105. 1901. 



2 For some notes on its flora see Bull. Torrey Club 30: 286-287. 1903. 



