82 



PHYSIOGRAPHY 



New York and the Carolinas are drowned valleys. Without the 

 drowning, the drainage of the region about Chesapeake Bay would 

 be somewhat as shown in Fig. 83. By comparing Fig. 83 with 82 

 it is seen that drowning separates the parts of a river system. 



Rejuvenation. If the basin of an old stream is raised so that 

 the gradient of the stream becomes greater, its velocity is increased, 

 and it again takes on the character of youth. Such a stream is said 

 to be rejuvenated. 



Ponding. If a part of the stream's bed is warped upward, the 

 flow above the up-warp is checked, and the stream widened. 

 Streams above such an obstruction are ponded; that is, the waters 

 accumulate in a pond or lake. If the up-warp is great enough, it 

 may completely dam the stream. Streams are also sometimes 

 ponded by lava-flows, by landslides, etc., and by dams made by 

 man. Mill-ponds along numerous creeks are illustrations of streams 

 ponded in the last of these ways. 



Piracy. One stream may steal another. One way in whicl 

 this is done has been suggested (p. 67). The stream which stej 



THE 



KITTATINNY 

 PLAIN 



THE 



5MENANDOAH 

 PLAIN 



Fig. 84. Fig. 85. 



Figs. 84 and 85. The capture of the head of Beaverdam Creek by the Shen- 

 andoah River. Virginia- West Virginia. (After Willis.) 



is a pirate. The stream stolen is diverted, and the stream which 

 has lost its upper waters is beheaded. Piracy has been much more 



