SOUTHERN APPALACHIAN REGION. 



121 



they contain have maintained the greatest elevations pre- 

 sented in this region. Of this the might}^ domes of the 

 Smokies, the Balsams, and the Roan, and the lofty peaks 

 of the Blacks, are witnesses. (PI. LXVI.) 



The moist atmosphere is conducive to the rapid decay gration. 

 of the rocks, which break up chiefly under the attack of 

 rain, frost, the roots of the trees, the underground waters, 

 and organic acids. At first decay works in along the vari- 

 ous partings, resulting in the loosening of large masses, 

 which gradually become smaller, until finally nothing is 

 left of them except clay and the more obdurate bits of 

 rock. The rocks reach the surface only over very small 

 patches, while in places the disintegration attains a depth 

 as great as 50 feet. On sloping surfaces the loose material 

 is maintained in its place solely by friction. When this 

 is lessened or overcome from any cause, the residual mat- 

 ter, be it clay or rock fragments, slides down the slopes 

 until the friction is again sufficient to retain it in one posi- 

 tion. Thus are formed immense thicknesses of loose mate- 

 rial washed down fi-om steep slopes and accumulated in 

 the hollows and flatter places. This material gradually 

 works its way downhill as it is pushed along bv the freez- 

 ing of the water which it contains, or is rendered more 

 unstable as the water ti"ansforms it into mud. Eventually 

 it finds its way into the streams and is carried by slow 

 stages into the sea. (PI. LXVII.) 



PROTECTION OF THE SOILS. 



The chief agent which checks this process of removal is 

 the forest cover, even though the penetrating roots and 

 the acids due to vegetation induce rock decomposition. 

 These same roots, however, hold the loose material in place 

 and hinder its tendency to slide downhill. With this Roots and 



lGfl.v6s protect 



assistance loose soils are upheld on slopes at angles fully the son. 

 double those which they could maintain unaided. Besides 

 this direct check to the waste of slopes by increased fric- 

 tion, the action of the forests is as great in another way. 

 Loose materials are washed downhill during rainstorms 

 by even the tiniest rivulets. In open fields these gather 

 in a few minutes and form deeper and deeper channels with 

 each succeeding storm, finally' removing the loose material 

 down to the bare rock. This process is almost wholly pre- 

 vented by the network of roots and the cover of leaves, both 

 living and dead, and the water concentrates into rivulets 

 by seeping through the soils so slowly that it carries no 



