106 HARPER 



(less than 13% of the angiosperms) is smaller than in any other 

 habitat-group here discussed. 



A study of the ranges of these plants brings out some inter- 

 esting facts. Quite a number do not extend farther into the 

 Altamaha Grit region than its very edge, but without exception 

 they all range farther inland. Only six species, Scutellaria 

 Mellichampii, Magnolia grandiflora, Myrica cerifera, Smilix 

 pumila, Dendropogon usneoides, and Pinus glabra, seem to be con- 

 fined to the coastal plain. All the rest (over 90% of the whole 

 list) therefore occur above the fall-line, and most of them grow 

 nearly all over the Eastern United States, a large proportion 

 finding congenial homes in the cool shaded valleys of the Blue 

 Ridge. 1 All this goes to show that the bluff -inhabiting species 

 are pretty old geologically, probably as old as any now living in 

 this part of the world. It is easy to imagine how they have 

 crept down along the rivers into the coastal plain as that territory 

 gradually emerged from the sea the last time, after the close of 

 the Pleistocene period. 



These river-bluffs evidently represent the extreme of mesophy- 

 tic conditions for the pine-barren region. It is noteworthy that 

 Fagus Americana, which Dr. Cowles considers the most typical 

 mesophytic tree of Eastern North America, does not yet occur 

 on these bluffs, or anywhere else in the Altamaha Grit region, 

 as far as known. It does occur however nearly everywhere 

 farther inland, and comes to the very edge of our region in 

 Decatur County at Forest Falls and along the escarpment from 

 Faceville westward, where the Chattahoochee formation crops 

 out. These places, and the vicinity of the Rock House in Dooly 

 County, where the geological conditions are doubtless similar, 

 (see page 17) have about the same kind of vegetation as the 

 river-bluffs, with most of the same species. 



Statistics of the Typical Habitat Groups. 



In the appended table are given in condensed form some of 

 the numerical statistics already elaborated for the 19 typical 



1 Their tendency to range northward is pretty well illustrated by the 

 frequency of such specific names as Americana, Canadensis, Marilandica, 

 and Virginiana. 





