HISTORY OF DERRYFIELD. 39 



With reference to more common examples of rock-wear, these 

 may be found at the various falls in this section to which allu- 

 sion has been made, and no finer instances of the action of run- 

 ning water are afforded this side of the upper Ammonusuc. At 

 Amoskeag this is exhibited upon a grand scale, and in a spring 

 freshet the rapids below the falls are not matched in grandeur 

 elsewhere in New Hampshire. Here the evidence is overwhelm- 

 ing as to the former existence of a rocky barrier, holding back 

 the water in a great lake basin, extending as far north as Hook- 

 sett. Beyond that point there is equally conclusive evidence of 

 the existence of two or more great lakes stretching northward, 

 with rock-dams at Garvin's and Sewall's falls, and another and 

 final barrier at Franklin, where the Pemigewasset and Winne- 

 pesauke unite. Further reference to examples of rock-wear per- 

 formed by pre-historic streams, and the part played by glacial 

 dams in the stupendous terrestrial drama, may be found in the 

 succeeding chapter. 



