22 HARPER 



accompanying map (frontispiece). The Altamaha Grit covers 

 about 11,000 square miles, including parts of twenty counties, 

 midway between the fall-line and the coast. Its inland edge is 

 quite sharply defined, always by a change in topography and a 

 less conspicuous but unmistakable change in flora, and in many 

 places by a bold escarpment besides. Its southern boundary in 

 Decatur and Thomas Counties is pretty well marked by the 

 change from open pine-barrens to the broad-leaved forests of the 

 Uppermost Oligocene region, but toward the southeast it is 

 impossible in the light of present knowledge to say just where 

 the Altamaha Grit terminates or disappears and the flat country 

 begins. This uncertainty makes little difference for the pur- 

 poses of this work, however, for very few species reach their 

 inland limits in the debatable territory. 



Geodetically the Altamaha Grit region (if confined to Georgia) , 

 is included between 30 45' and 32 50' north latitude and 8i° 25' 

 and 84 50' west longitude. In altitude above sea-level it ranges 

 from about 400 feet where the escarpment intersects the 

 Atlantic and Gulf divide to 50 or 75 feet on the southeast, and 

 there are consequently no alpine or maritime elements in its 

 flora. 



Geology and Soils. 



The Altamaha Grit is probably of Pliocene age, as stated 

 above. Outcrops of the characteristic rock are comparatively 

 rare, constituting probably not more than one hundredth of 

 one per cent of the entire area, but they have been 

 seen or heard of by the writer in nearly every county in the 

 region. 



The outcrops occur either on hillsides in the open pine-barrens, 

 in beds of streams, or on river-banks. The hillside outcrops 

 show usually a fine-grained conglomerate consisting of small 

 quartz pebbles and grains of sand cemented together with argil- 

 laceous material. Chemically it must be composed of silica and 

 alumina, with some iron oxide, but very little if any calcium 

 carbonate. A fresh surface of the Grit (at least the upland phase 

 of it) is yellowish with coarse red mottlings, but it all weathers to a 



