ALTAMAHA GRIT REGION OF GEORGIA 9 



Most of the papers hitherto published on the subject deal only 

 with the more immediate and obvious effects of geology on 

 vegetation, acting mainly through the physical and 5 chemical 

 composition of the soil. The more remote and subtle — -but no 

 less important — effects of topography and geological history 

 have not attracted so much attention, but it is one of the pur- 

 poses of this thesis to discuss some of them for the region under 

 consideration. 



Geological Divisons. 



As the geological divisions of Eastern North America are not 

 often mentioned in botanical literature, a brief outline of them 

 may be of interest. 1 In the order of age, they are as follows: 



i. The Metamorphic region, with two subdivisions, the Pied- 

 mont and the Blue Ridge. The former extends nearly in a 

 straight line from Pennsylvania to eastern central Alabama, in 

 a belt averaging about ioo miles in width. Its underlying rocks 

 are mostly granite and gneiss and its soil a deep red clay. It 

 contains little if any limestone. That portion of the Piedmont 

 region included in Georgia is known as Middle Georgia. 2 It is 

 everywhere hilly, but scarcely mountainous, though a few 



Dall, W. H. (Geology of Florida). Bull. 84, U. S. Geol. Surv. 95 

 (near top), 1892. 



Small, J. K. Studies in the Botany of the Southeastern United States — 

 I. Bull. Torrey Club, 21: 15, 1894. (One reference only.) 



Maxon, W. R. On the occurrence of the Hart's Tongue in America. 

 Fernwort Papers 30-46. 1900. 



Mohr, C. The spontaneous flora of Alabama in its relation to agricult- 

 ure. Contr. U. S. Nat. Herb. 6: 821-824. 1901. 



Macbride, T. H. The Alamogordo Desert Science II. 21: 90-97. 

 Jan. 20, 1905. 



1 For recent maps showing some of these divisions see one by W. M. 

 Davis in Mill's International Geography, p. 719, fig. 353, 1900; also 

 fig. 191 in Dodge's Advanced Geography, 1905. 



2 For some notes on the flora of a typical portion of Middle Georgia 

 see Bull. Torrey Club 27: 320-341. 1900. The plants of the corre- 

 sponding portion of Alabama have been enumerated by Prof. Earle in 

 Bull, iiq, Ala. Agric. Exp. Sta , 1902. The physiography and geology 

 of Middle Georgia are discussed by T. L. Watson in Bull. Geol. Surv. 

 Ga. 9A: 60-65 ^902. 



