36 CONTRIBUTIONS TO THE 



then for only a few hours at a time. So that this particular ex- 

 cavation must be singled out with confidence as having been 

 formed by a pre-historic stream, flowing at a level very much 

 above the known water-lines of to-day, and in a time so remote 

 as to be conjectural, if not at once referred to a glacial epoch 

 ante-dating that under discussion. 



There are some remarkably significant facts connected with 

 the group of pot-holes we are considering. In the first place the 

 larger part of them occur in the bottom or bed-rock ; again, they 

 were found just as they now appear when the first dam was 

 built upon the stream above them. They remain precisely in 

 the form of their first discovery by the early salmon-fishers, not 

 less than two centuries and a half ago. Old residents at the falls 

 unite in the statement that so far as their observation or knowl- 

 edge extends there has been no change in their number and 

 character. It is altogether probable that under the required 

 conditions pot-holes are somewhere even now being made, but 

 there is not the slightest evidence here of the formation of new 

 ones within the historic period. 



Beautiful and symmetrical examples of pot-holes are likewise 

 found at Hooksett and Goffe's falls on the Merrimack, at Kelly's 

 falls on the Piscataquog, and at a point on the latter stream near 

 Arcadia, where there was formerly a dam. 



We have examined a pamphlet by Bouv6, entitled "Indian 

 Pot-Holes," in which the writer sets up an ingenious theory as 

 to the manner of their formation. He conceives that some may 

 have been formed by plunging falls, descending from a sufficient 

 height, proceeding from ice-fissures, and continued long enough 

 to produce the effects. He concedes the difficulty of requiring 

 the ice-sheet to remain stationary, but offers nevertheless no 

 other explanation. It is certain that continued plunging falls 

 will excavate remarkable basins in rock-floors upon which they 

 impinge ; these are frequently very symmetrical, and the rock- 

 wear has undoubtedly been in part produced by stones carried 



