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 this 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 published in 

 vol. 9thf of the American Journal of Science," &c. 



* Silliman's Journal, vol. 9. 



•f The above explanation, in nearly the same terms, will be 

 found in our published account of the phenomenon in Silliman's 

 Journal. 



