THE WORK OP STREAMS 



169 



of invasion will 

 become tribu- 

 tary to it, for 

 it will afford 

 them a lower 

 line of descent. 

 In Figure 175 

 this has oc- 

 curred. The 

 process by 

 which it was 

 accomplished 



FIGS. 174, 175, 176. Diagrams to illus- 

 trate stream piracy. 



FIG. 173. Drainage in a re- 

 gion of folded rocks. 



is known as stream piracy. 

 The stream which effected 

 the capture is the pirate, 

 while the stream which 

 suffered the loss is called 

 a beheaded stream. The 

 drainage captured is said 

 to be diverted. The sud- 

 den increase in its vol- 

 ume has permitted the 

 pirate (Fig. 175) to cut 

 a new valley in the bot- 

 tom of its old one, and 

 the remnants of the old 

 valley flat now form ter- 

 races. Favored by the 

 lower level afforded by 

 the pirate, the diverted 

 streams have lowered 

 their valleys notably, ex- 

 cept above the upper 



