102 HARPER 



hammock flora ranges farther inland than the Altamaha Grit 

 region, 78% grows in the upper fourth of the coastal plain (i.e., in 

 the Cretaceous and Eocene regions), and 45% crosses the fall-line. 

 Most of the trees and shrubs are also characteristic inhabitants 

 of rich woods in the Eocene region. 



It is evident from these statistics that the species now inhab- 

 iting the hammocks have mostly come in from other places which 

 are farther north and farther inland (and consequently cooler 

 and more elevated). The fact that they tend to flower early, as 

 already shown, is pretty good evidence that they range mostly 

 toward cooler climates. As many of them are now also perfectly 

 at home in places which were not submerged during the time 

 that the Columbia sand was being deposited, they doubtless an- 

 tedate that period, and are therefore older than the typical pine- 

 barren species are supposed to be. 



As the typical hammock plants have evidently arrived in the 

 region under consideration since the sand-hills were formed, it 

 is reasonable to suppose that others are still coming in, and that 

 if unmolested the hammocks a few thousand years from now 

 would be more extensive and have a richer flora than at present. 

 It is an interesting fact that most of the hammock plants which 

 have been noted in the region but once or twice are known 

 only in the uppermost counties, as may be seen by consulting 

 the catalogue of species. This alone would seem to indicate 

 that they are still on their way toward the coast. 



Taxonomically the list shows 65 species belonging to about 

 57 genera and 42 families. No family has more than four re- 

 presentatives, and no genus more than three. There are only 10 

 monocotyledons, which is about 17% of the total angiospermous 

 flora of the hammocks. 



19. River Bluffs. 



The muddy rivers which traverse the Altamaha Grit region 

 (i. e., the three largest ones, which rise in the Piedmont region) 

 are bordered in places by steep bluffs (plate XII, fig. 1), formed 

 by erosion in much the same way as other bluffs the world over. 

 These bluffs are best developed at or near the inland edge of our 

 territory (where the Chattahoochee formation probably crops 



