STREAMS AXD THEIR WORK 



177 



term is meant the low lalid along a stream that is 

 flooded in time of high water. A flood-plain is formed 

 by the stream widening its valley by erosion on the 

 sides. If the stream has not lowered its bed to the 

 level where lateral erosion can take place, it is in a 

 stage of youth. 



FIG. 69. Waterfall in Catskill Mountains, New York. 



Sixth, waterfalls are frequent along -the courses of 

 young streams. To produce a waterfall there must 

 be a hard stratum of rock over which the stream is 



