124 



GEOLOGY 



doah River then worked back and tapped Beaverdani deck. 

 diverting its head waters to the Potomac (Fig. 88). The youn^ 

 Shenandoah was a pirate, and Beaverdam Creek was beheaded. 

 The stream to which waters are diverted is increased in size, and 

 the beheaded stream is correspondingly diminished; or if its total 

 supply of water came in above the point of tapping it would dis- 

 appear altogether. 



An actual case of piracy is shown on Plate IV. North and 

 South Lakes formerly drained westward to the Schoharie Creek, 



THE 



KITTATINNY 

 PLAIN 



THE 



5HCNANDQAH 

 PLAIN 



Fig. 87. 



Fig. 88. 



Figs. 87 and 88. The capture of the head of Beaverdam Creek by the Shenan- 

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



the present head of which is in the extreme northwest corner of 

 the map. The head of Kaaterskill Creek, which had a much higher 

 gradient, worked back and captured the head of the westward-flow- 

 ing stream, diverting the drainage from North and South Lakes i < > 

 itself. Schoharie Creek was thus beheaded. 



Plaatekill Creek, near the south limit of the map, appears to 

 have beheaded the creek flowing west and northwest, similarly 

 diverting its head waters. 



A Cycle of Erosion 



From what has preceded it is clear that the topography of a 

 region undergoing erosion will change greatly from time to time. 



