16 PHYSICAL GEOGRAPHY OF 



we must bear in mind that there is a continuous slope, approximating to that of 

 a great plane, and extending from the summit of the Alleghany range, continued 

 south, down to the bed of the Ohio. But the prolongation of that dividing range 

 sweeps round through the western end of North Carolina and the northern por- 

 tions of Georgia and Alabama, until it acquires a nearly due west direction 

 along the southern bend of the Tennessee river. In fact, this great stream 

 follows the course of the mountain range which divides the waters of the Atlantic 

 from those of the Mississippi, and serves to mark its general outhne. 



Cumberland river then sweeps in an interior circle, concentric to the bend of 

 the Tennessee, and consequently rests lower down upon the great slope which 

 extends from the summit of the dividing range to the vale of the Ohio. 



It occupies a lower level than the Tennessee ; while Green river follows 

 yet an interior circle, concentric both to the sweep of the Cumberland and that 

 of the Tennessee, and rests nearer to the foot of the same great plane than 

 either of the exterior rivers, and approaches consequently closer in position and 

 level to the bed of the Ohio. 



If we proceed from the Ohio in a south or south-eastern direction, crossing 

 the valleys of Green river, the Cumberland, and the Tennessee, successively, 

 we shall be constantly ascending to a higher and higher level ; although the 

 route leads over many intermediate elevations and depressions, all resting on the 

 same common slope, which, as before explained, extends from the crest of the 

 dividing ridge to the valley of the Ohio. 



For this cause — resting near the foot of the great plane, and running nearly 

 parallel with the course of the Ohio — Green river has a descent less rapid 

 than that of the more elevated beds of the Cumberland and Tennessee, and 

 more rapid than that of the Ohio. 



Kentucky river is the next important tributary which we find on ascend- 

 ing towards the north. The distance by the meanders of this stream, from 

 Three Forks to its mouth, is 257^ miles, and the total fall 216 feet, or 10 inches 

 per mile. 



The slope of the Ohio between Cincinnati and Louisville is 4^ inches per 

 mile, in accordance with the usual relation between the fall of that stream and 

 the rates of descent of its navigable tributaries. 



Licking river, Big Sandy, and the Guyandotte, can hardly be called navi- 

 gable rivers. They are streams of an inferior class, and obey a rule so general, 

 that it almost amounts to a law, viz., that, under like circumstances, the smaller 

 the tributary of the Ohio the greater is its descent; a rule which holds, with few 

 exceptions, whether the branch enter directly into the principal stream, or reach 

 it indirectly through an affluent of superior magnitude. The largest streams 

 run in the lowest valleys, as if they had made for themselves the deepest chan- 

 nels in the earth. 



The Licking river, from West Liberty to the Ohio, a distance of 231 miles, 

 falls 316 feet, or 16| inches per mile; while Guyandotte river, from Logan's 

 court-house to the Ohio, a distance of 74 miles, falls 142 feet, or 23 inches per 



