142 On the Movement of Rocks, 



near the edge of grounds covered by water during the 

 winter, have considerably inclined towards the shore as 

 soon as the ice was formed, and fences in this situation 

 always require to be placed upright in the spring. It is 

 well known among the farmers of New-England, that, if a 

 stone fence is erected in a similar situation, it will after 

 some time be overturned. These instances, show both 

 the reality and great force of expanding ice. It is no ob- 

 jection to this explanation, that the principal rock which 

 Dr. Dwight saw, was originally, according to the testimo- 

 ny, two feet at least under the surface of the water, be- 

 cause in New- England the ice sometimes forms three feet 

 in thickness, which would be sufficient to form about this 

 rock, and also for aught that appears to the contrary, about 

 those mentioned in the Massachusetts Transactions. The 

 firmness with which ice attaches itself to rocks, may be 

 estimated from the circumstance, that those of many tons 

 weight are sometimes raised from the beds of rivers, where 

 the ice reaches to the bottom, and carried imbedded in 

 the ice to a great distance. (Edin. Encyc. X, 773.) 



It appears also by the testimony, that the principal rock 

 now moves much more rapidly than many years since, and 

 this is what might have been expected according to the 

 explanation I have suggested. When the top was " two 

 feet at least" below the surface, only the thickest forma- 

 tions would reach it, and of course its progress would be 

 very slow. When the top reached the surface, the thin 

 formations would affect it, and when it rose above the sur- 

 face, it would be grasped in the middle by every successive 

 formation, and would be carried forward by the whole 

 amount of the expansion. Your unknown correspondent 

 Petros says, that " twelve years ago it moved but five feet 

 in a year," while according to a measurement given by 

 him it was moved about 3 rods between Sept. 1819, and 

 Feb. 13th, 1821. The extent of its motion during this 

 period is more than I should have expected, but probably 

 during the two winters embraced in it, the ice formed and 

 melted an uncommon number of times. 



The circumstances of the channels behind the rocks, and 

 the earth heaped up before them, render two things evi- 

 dent : First, that each rock was always moved in a position 

 similar to itself, without ever being turned over ; for if the 



