DAVIS: RIVER TERRACES IN NEW ENGLAND. 345 



river to open a broad flood plain enclosed by strong scarps, as typified 

 in Figures 2 and 22 ; while further south the valley exhibits the com- 

 plete control exercised upon a swinging river by the chance discovery 

 of ledges during the progress of degradation. This process is shown 

 to have been gradual by the preservation of flood-plain remnants at 

 various heights, wherever ledges are present to defend their bases ; yet 

 so complete is the destruction of the plains at intermediate levels just 

 above Concord that one might there infer that the river had had no op- 

 portunity to swing laterally until the opening of the present flood plain 

 was be<nin. 



