ALTAMAHA GRIT REGION OF GEORGIA 19 



The topography and flora of this region will be discussed in 

 detail farther on. 



7. Uppermost Oligocene. Just south of the Altamaha Grit 

 country in Decatur and Thomas Counties, and perhaps also in 

 Brooks and Lowndes, are strata belonging to the Alum Bluff 

 group, 1 which is probably the uppermost member of the Oligocene 

 series in Georgia. It passes southward into Florida, where it 

 is said to be conformably overlaid by Miocene strata toward the 

 Gulf. Its eastern and western limits are not known. The rock 

 of this region is an impure limestone, and the topography is 

 quite rugged, compared with the rest of the coastal plain. In 

 Decatur County (I have not studied it much elsewhere), the 

 soil is almost entirely red loam, presumably Lafayette, and 

 broad-leaved forests (in which Magnolia grandifiora is usually 

 conspicuous) predominate, Pinus palustris being correspondingly 

 scarce. The whole aspect of the country strongly suggests the 

 Eocene region a hundred miles farther north. 2 



8. Southern Lime-sink region. In the southern part of 

 Lowndes County (and probably also in Brooks and Echols and 

 adjacent Florida) is a lime-sink region having much the same 

 character as the Lower Oligocene lime-sink region already men- 

 tioned, and containing some of the largest ponds in the state. 3 

 Geologically this region seems to have Lower Oligocene lime- 

 stone strata near enough to the surface to exert a decided influence 

 on the topography, but overlaid by a thin layer of Altamaha 

 Grit, and doubtless also by Lafayette and Columbia in most 

 places. 



9. Flat pine-barrens. Towards the coast the Altamaha Grit 

 region passes gradually into a country so nearly level that there 

 is little distinction between wet and dry pine-barrens, swamps, 

 ponds, and streams (except the rivers). This region includes 

 Okefinokee Swamp, and stretches coastward about to tide-water. 

 It also extends westward at least to Lowndes County, and north- 

 eastward and southward beyond the borders of the state. It 



1 According to Vaughan, Bull. U. S. Geol. Surv. 213: 392. 1903. 



2 For a few additional notes on the Uppermost Oligocene region see 

 Bull. Torrey Club, 30: 289-335. 1903. 



3 See Bull. Torrey Club 31: 14, 15, /. j. 1904. 



