70 WORK OF RUNNING WATER 



infant valley is the gully or ravine (Fig. 40). It has steep slopes and 

 a narrow bottom. Plate III represents somewhat older ravines, 

 in contour. As a valley is widened, lengthened, and deepened, 

 it passes from infancy to youth. In this stage also the valleys are 

 relatively narrow, and the divides between them broad. The valleys 

 may be deep or shallow according to the height of the land in 



Fig. 59. Canyon of the Yellowstone below the falls. Yellowstone Park. 



which they are cut, and the fall of the water flowing through them; 

 but in any case the streams flowing through them have done but 

 a small part of the work they are to do before the country they 

 drain is base-leveled. Figs. 58 and 59, respectively, represent 

 youthful valleys in regions of slight and great relief. Fig. i, PI. V, 

 shows youthful valleys in a region of slight relief, and Fig. 2, PI. V, 



