438 UNIVERSITY OF VIRGINIA PUBLICATIONS 



of meandering streams some lateral planation may occur with the down 

 cutting at an early stage in the cycle. Thus North River near Bridge- 

 water, Rockingham County, has considerably increased the distance 

 between it and Round Hill on one side since the inauguration of the 

 present cycle, and on the other side it has invaded the hill itself — the 

 difference in the two cases being due to the position of the hill with refer- 

 ence to the meanders of the stream. 



Three fairly typical examples illustrating different stages in the process 

 of stream capture by lateral planation are described below. By consult- 

 ing the accompanying topographic maps (figs. 1, 2, and 4), it will be 

 observed that each of these cases is found in a rejuvenated region. The 

 stage of development represented in the present cycle in these cases appar- 

 ently ranges from late youth to maturity. The first case described is in 

 Dickenson County in the Alleghany Plateau region of southwest Virginia. 

 The capture has not yet taken place, but geological^ speaking it is immi- 

 nent. The second case illustrates the same type of capture in process of 

 taking place, and the third shows that it has already occurred. The 

 last two cases are in Rockingham County in the Shenandoah Valley. 



The type of stream piracy illustrated by these three cases is designated 

 by the writers the intercision type. The term intercision was used by 

 Goldthwait* in describing a peculiar change in drainage near Kenosha, 

 Wisconsin, where the narrow divide between Lake Michigan and the 

 lower part of the meandering valley of Pike River has been removed in 

 places by the combined work of the lake and stream, and the lower part 

 of the stream severed from its upper course. 



Case I. The accompanying topographic map (fig. 1) of a small area 

 in Dickenson County, southwest Virginia, shows the existing topographic 

 conditions in this case. The rocks are sandstones and shales and are 

 very gently folded. The region is thoroughly dissected but the streams, 

 which are of the rejuvenated type, are actively engaged in eroding their 

 valleys deeper. The streams have inherited meandering courses from a 

 previous cycle. 



It will be observed by consulting the map (fig. 1) that a meander in 

 the valley of Pound River at a point about 3 miles from its junction with 

 Russell Fork brings it very close to that of one of its tributaries. Cane 

 Branch. The minimum distance between the two streams is about oOO 

 feet, and Pound River is flowing at a level more than 100 feet below its 

 tributary (Cane Branch). The divide between the two streams is being 



* Goldthwait, J. W., Intercision, a peculiar kind of modification of drainage. 

 School Science and Mathematics, 1908, vol. 8, no. 2, pp. 129-139. 



