130 



GEOLOGY 



drain is base-leveled. Figs. 95 and 96, respectively, represent 

 youthful valleys in regions of moderate and great relief. Fig. IJ 

 PL VI shows youthful valleys in a region of slight relief, and Fig. 2,J 

 PL VI, in a region of great relief. The uppermost line in Fig. 8 

 likewise represents topographic youth, as shown in cross-profile. 



Fig. 96. The canyon of the Yellowstone below the falls. 



National Pink. 



Not only are narrow valleys said to be young, but the territory 

 affected by them is said to be in its topographic youth, since but a 

 small part of the time necessary to reduce it to base-lovH has 

 elapsed. An area is in its topographic youth when considerable 

 portions of it are still unaffected by valleys. Thus the arc. 



