ALTAMAHA GRIT REGION OF GEORGIA 23 



dull reddish brown, almost exactly the color of pine bark (a very 

 appropriate resemblance, one might say). 1 The rock is not very 

 hard, and can easily be broken up with suitable tools. It finds 

 some use locally for curbing and foundations. 



Where it is exposed on river-banks (near Mount Vernon and 

 Lumber City for instance) it has quite a different appearance 

 from the hillside outcrops, being apparently softer and more 

 homogeneous, with a greenish tinge. But many other coastal 

 plain rocks show an equal diversity between their river-bank 

 and upland outcrops. 



When thoroughly decomposed by atmospheric agencies the 

 Grit can often hardly be distinguished from the Lafayette loam, 

 and in railroad cuts and other artificial excavations which ex- 

 pose the indurated Grit it is sometimes impossible to say whether 

 there is any Lafayette above it or not. 



The Lafayette probably covers more than 99% of the Altamaha 

 Grit region, but its presence cannot easily be proved, for the 

 reason just stated, and also because neither it nor the Grit is 

 fossiliferous. Little if anything is known as to its maximum 

 thickness in this region. In composition it is a loam, containing 

 probably as much sand as clay. Farther inland it is often 

 brick-red, but in the Altamaha Grit region, and in pine-barrens 

 generally, its color is considerably lighter and might be de- 

 scribed as terra-cotta. 



The Columbia formation is nearly everywhere present, varying 

 in thickness from 25 feet or more in the sand-hills to nothing on 

 rock outcrops and on some of the ridges. It consists of nearly 

 pure sand, probably containing very little plant-food. Where 

 not mixed with humus it is white or very pale buff. 



The distinction between the Lafayette and Columbia formations 

 is very familiar to the natives, who know that if they want clay 

 for any purpose they can get it anywhere by digging through a 

 few inches or feet of sand. 



Unlike the older parts of the coastal plain, the Altamaha Grit 

 region contains almost no traces of limestone, judging from the 

 nature of the vegetation. 



1 See also Bull. Torrey Club, 32: 144. 1905. 



