Stream Piracy 



73 



A CASE OF STREAM PIRACY NEAR GREENCASTLE, 



INDIANA. 



Ernest Rice Smith, DePauw University. 



In the course of topographic mapping- by the class in General 

 Geology, DePauw University, in the fall of 1922, the following case 

 of piracy was noted and studied by the students mapping this area. 

 I desire to express my appreciation to Miss Helen I. Tucker and Mr. 

 Robert L. Allen of the class in Field Geology, 1923, for their careful 

 topographic map of the area. This area deserves attention, not be- 



Fig. 1. The approximate drainage relations before piracy began. 



cause of the magnitude of the phenomenon involved, but as an evidence 

 of the general presence of important geological phenomena, even in 

 areas which seem very bare of certain phases of geologic interest. 



As noted in text books of Geology, conditions are ripe for piracy, 

 where two adjacent drainage systems or parts of the same drainage 

 system have unequal opportunities in the struggle for existence. Any 

 factor which gives one stream the advantage over another stream is 

 thus a contributing cause to piracy. Such factors may be: steeper 

 gradient, greater rainfall, less resistant rock, etc. A complete study 

 of any case of piracy should involve not only a statement of the 

 physiographical history of the piracy, but also the points of superiority 

 of the one drainage system over the over. In the present case, the 

 physiographical history is so plainly written by the hand of nature, 



"Proe. Ind. Acad. Sci., vol. 33, 1923 (1924)." 



