INTRODUCTION. 
23 
near James river, it is 1200 feet in the region of the sources of the Ca- 
tawba. In the interior of the mountain regions the deepest valleys re- 
tain an altitude of from 2000 to 2700 feet. From the dividing line in 
the neighborhood of Christiansburg and at the great bend of Hew River 
the orographic and hydrographic relations undergo a considerable modi- 
fication. The direction of the principal parts of the system is also some- 
what changed. The main chain which borders the great valley on the 
east, and which more to the north, under the name of the Blue Ridge, 
separates it from the Atlantic plain, gradually deviates towards the south- 
west. A new chain detached on the east, and curving a little more to 
the south, takes now the name of Blue Ridge. It is this lofty chain, the 
altitude of which, in its more elevated groups, attains gradually to 5000 
and 5900 feet, which divides in its turn the waters running to the At- 
lantic from those of the Mississippi. The line of separation, of the east- 
ern and western waters, which, to this point, follows either the central 
chain of the Alleghanies, or the table-land region, passes now suddenly 
to the eastern chain, upon the very border of the Atlantic plain. The 
reason is that the terrace which forms the base of the chains, and the 
slope of which usually determines the direction of the water-courses, at- 
tains here its greatest elevation, and descends gradually to the northwest. 
The base of the interior chain, which runs alongside the great valley, is 
thus depressed to a lower level, and though the chain itself has an abso- 
lute elevation greater than that of the Blue Ridge, the rivers which de- 
scend from the summit ol this last, flow to the northwest towards the 
great central valley, which they only reach in southern Virginia and 
North Carolina, by first passing across the high chain of the Unaka and 
Smoky Mountains through gaps of 3000 to 4000 feet in depth. 
The southern division thus presents from southeast to northwest three 
regions very distinct. The first is the high mountainous region com- 
prised between the Blue Ridge and the great chain of the Iron, Smoky 
and Unaka mountains, which separates North Carolina from Tennessee. 
It commences at the bifurcation cf the two chains in Virginia, where it 
forms, at first, a valley of only ten to fifteen miles in breadth, in the 
southern part of which flows New river ; it then enlarges and extends 
across North Carolina and into Georgia, in length more than 180 miles, 
varying in breadth from twenty to fifty miles. The eastern chain, or 
Blue Ridge, the principal water-shed, is composed of many fragments 
scarcely connected into a continuous and regular chain. Its direction 
frequently changes and forms many large curves. Its height is equally 
irregular. Some groups, elevated some 5000 feet and more, are sepa- 
rated by long intervals of depression, in which are found gaps, whose 
