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 
r. Dwight saw, was originally, according to the testimo-~ 
ny, two feet at Jeast 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 | 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 
riod 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 ina position 
similar to itself, without ever being turned over ; for if the 
