THE WORK OF RUNNING WATER. 



85 



slopes and a narrow bottom. Fig. 1 of Plate IV represents similar, 

 or rather older, ravines in contour (shore of Lake Michigan, just north 

 of Chicago). With age, the valley widens, lengthens, and deepens, and 



Fig. 68. — A gully somewhat older than that shown in Fig. 67. (Alden.) 



Fig. 69. — A young valley in a region of slight relief. 



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

 tively narrow, and the divides between them broad. They may be 



