152 
EXPANSION OF ICE. 
In the year 1819 we first discovered the impor- 
tant fact, that large masses of rock lying near the 
shores of ponds and lakes are moved towards the 
land by the expansion of the freezing ice. This 
was in Salisbury, Connecticut, where, in the north 
part of the town, may be seen two large ponds, sep- 
arated from each other by a narrow strip of land, 
or, rather, rocks and stones, which have evidently 
been crowded from the bed of the lake by the same 
cause. By actual measurement on the ice, we as- 
certained that a rock weighing several tons was 
moved, during the space of one very cold night in 
January, several inches. Since then the same fact 
has been observed in Scotland and other places.* 
In respect to this phenomenon. Prof. Hitchcock 
observes, " I am not aware that this phenomenon 
has been noticed on the eastern continent, and it 
has been but rarely observed on our own. It is 
well known that water, by an apparent exception 
to a general law, expands with great force when 
freezing, and even far below the freezing point. 
Over a large extent of surface this effect may be 
very considerable ; and when bowlder-stones, lying 
in shallow ponds, become partially enveloped in the 
ice, they must feel the effect of this expansion, and 
be driven towards the shore, since the force must 
always act in that direction. As no counter force 
exists to bring back the rock to its original position, 
the ultimate effect must be to crowd it entirely out 
of the pond ; and, perhaps, to tliis cause we may 
impute the fact, that on the margin of some ponds 
we find a ridge of bowlders ; while the bottom, for 
a considerable extent, is free from them. The re- 
moval of rock masses in this manner was first noti- 
ced in Salisbury, Ct., and a statement pubHshed in 
vol. 9tht of the American Journal of Science," &c. 
* Silliman's Journal, vol. 9. 
t The above explanation, in nearly the same terms, will be 
found in our published account of the phenomenon in Silliman's 
Journal. 
