442 UNIVERSITY OF VIRGINIA PUBLICATIONS 



Dry River, a tributary of North River, likewise crosses this ridge 

 about three-fourths of a mile northeast of the junction of the two streams. 

 The point in the ridge where it is crossed by Dry River is less cherty than 

 in the vicinity of North River and therefore Dry River, although the 

 smaller of the streams, occupies the larger of the two valleys. 



The peculiar feature in the case of Dry River after passing the cherty 

 ridge is that it has abandoned the lower portion of its valley which was 

 developed in less resistant rocks, flows back again into the cherty ridge 

 area and joins North River more than half a mile above the point where 

 the latter stream leaves the ridge. 



The almost level plain south of the Chesapeake and Western Railwaj' 

 is the abandoned southern extension of Dry River valley. This plain 

 is composed of alluvial material, such as sand, gravel, loam, clay, and in 

 places numerous large river boulders. There are also traces of stream 

 channels in the form of linear and meandering depressions. The boundary 

 between this plain and the present flood plain of North River immedi- 

 ately above and below Bridgewater is marked by a distinct terrace with 

 an average difference in elevation of 10 to 20 feet between the two plains. 

 This terrace can be traced all the way from the point where North River 

 emerges from the cherty ridge to the vicinity of Berhnton, a distance of 

 1^ miles. 



The explanation of this interesting physiography is that Dry River 

 formerly entered North River near Berlinton about IJ miles below their 

 present junction. For some distance above their old junction the two 

 streams had a common flood plain, but at the point of their present junc- 

 tion their valleys were separated by a narrow cherty ridge. Finally a 

 breach was made in this cherty ridge by the two streams which had swung 

 against it at opposite points. Since North River was the larger stream- 

 and therefore flowing at a lower level it captured the waters of Dry River. 

 The streams do not meet at grade but there is a fall of 2 or 3 feet in Dry 

 River a few yards above their junction. 



The results of the capture were the abandoning of the valley of Dry 

 River between the point of capture and the old junction, and the rejuve- 

 nation of that part of North River between these points by increase in 

 volume of water. The result of this rejuvenation has been the marked 

 lowering of the flood plain of North River between the point where it 

 leaves the cherty ridge and Berlinton. The present flood plain of North 

 River is 10 to 20 feet below the level of the common flood plain of the 

 two streams before the capture took place. 



