THE WORK OF RUNNING WATER 327 



from its basin lowers the basin about one foot in 5000 

 years; but the material which is dissolved increases the 

 amount carried away, so that the basin is lowered a foot 

 in from 3000 to 4000 years. 



THE BAD LANDS OF DAKOTA. 

 Running water has so dissected this land as to render it valueless. 



The channels of some of the streams in this basin are 

 cutting down with far greater rapidity than this. We 

 see gullies cutting down -little troughs for themselves 

 several inches deep in one rainstorm. The rapidity of 

 cutting depends upon the material, the slope and the 

 quantity of water. That " the waters wear the stones " 

 was noted even in Job's time. 



