DRAINAGE MODIFICATIONS 669 



ment of the minor drainage lines, hence a study of these will 

 be best facilitated by an accurate drainage map. 



Numerous cases of such adjustments can be found in the 

 streams of the Mississippi Valley, where the general horizontal- 

 ity of the rocks keeps the problem free from great complica- 

 tions. In this region we find many cases of the migration of 

 divides and the complete rearrangement of the drainage lines. 



{^a^ Kanaivha River basin. — A noteworthy case of this kind, 

 occurring in the central portion of West Virginia, is shown in 

 Fig. II, and has been described in the previous portion of this 

 paper as a t3'pe example of its kind. A K (Fig. 11) is the 

 Kanawha River, K B C is the Gauley River, A D G \s the Elk 

 River, and H I J is the Little Kanawha River. The first two 

 streams belong to the Great Kanawha system and the last 

 to the Little Kanawha or Ohio River system. As previously 

 explained, the divides have migrated toward the southeast, until 

 in places they are within a mile of the stream next above. It 

 will be noticed that this action is much more effective near the 

 heads of the streams, for at this point alone has capture resulted. 

 Lower down, the divide still remains close to the stream above, 

 but diverges more and more until, as it approaches the mouths 

 of the streams, it is about equally distant from the stream above 

 and the stream below. This is doubtless due to the fact that 

 most of the shifting occurred when the region was uplifted and 

 tilted, after the cutting of the extensive peneplain which is a 

 marked feature of the region. The large volume of water in the 

 lower courses of these streams enabled them to maintain their 

 former courses and quickly intrench themselves within the tilted 

 plain. Since then their cutting has been so rapid that it has 

 overbalanced all of the effects of the tilt; consequently their 

 basins, in this portion of their courses, are approximately sym- 

 metrical. Farther up the streams, where the volume of water 

 was less, the streams were unable to so fortify themselves, and 

 consequently were dispossessed of most of their territory by 

 their lower neighbors. At their extreme heads, the streams 

 were held for a long time on the surface of the peneplain, and 



