170 A, Guyot on the Appalachian Mountain System. 
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 general direction of the water courses, 
attains here its greatest elevation, and descends gradually to 
wards 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 absolute elevation greater than 
' that of the Blue Ridge, the rivers which descend from the sum- | 
mits of this last, flow to the northwest towards the great central 
see. It commences at the bifurcation of the two chains in Vil- 
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tion as far as the Bald mountain separate the basin of the Nole- 
chucky from that of the French Broad river. Between the ! 
