SOUTHEEN APPALACHIAN REGION. 



119 



regard to the moist, warm winds from theGulf combines with 

 a general altitude unequaled east of the Mississippi to pro- 

 duce a unique and remarkable vegetation. (PI. LXIV.) 



THE GEOLOGIC FORMATIONS. 



The geologic formations which underlie this mountain 

 district may be divided into four large groups. Each dif- 

 fers widely from the others in age, and has very distinct 

 features of its own. These broad differences have ex- 

 pressed themselves in such major topographic features as 

 the Appalachian Valley, the Appalachian Mountains, and 

 the Piedmont Plateau. These differences are also largely 

 responsible for the principal variations in the character of 

 the surface in the mountain district itself. 



The Appalachian Valley is underlain by a series of lime-^j.^^^p'^^^'^o"^ 

 stones, shales, and sandstones, mainly of late Cambrian 

 and Silurian age, forming the youngest of the four groups 

 in this region. Small outliers of these formations ai'e in- 

 cluded within the area of the mountains near the border 

 of the Appalachian Valley. 



The second group occupies the northwestern border of g^^p «• ^ t ^ i t e 

 the mountain district, chiefly northeast of the French 

 Broad Rivei'. It consists of a series of quartzites, sand- 

 stones, conglomerates, and shales of Lower Cambrian age. 

 A second lai'ge area of these rocks occupies the Blue 

 Ridge and adjacent territory, nearly in the center of this 

 district. 



The third group is of Cambrian age. It occupies the group°^^°™'^'^^^*^ 

 northwest border of the mountain mass, corresponding in 

 position to the previous group but best developed south- 

 west of the French Broad River in the Smoky and Unaka 

 mountains. The group consists of conglomerates, gray- 

 wackes, sandstones, schists, and slates, and is called the 

 Ocoee group. This and the preceding two groups were 

 composed of the waste from older rocks, which was de- 

 posited under water. The thickness of the strata is ap- 

 proximately the same in the Ocoee group and the formations 

 of the Appalachian Valley. The Lower Cambrian quartz- 

 ites and shales of the second group have only from one- 

 fourth to one-third of the thickness of either of the 

 preceding groups. 



The fourth group is much the largest of all, both in actual 

 bulk and area. It consists in the main of formations of 



