124 



Scientific Geology. 



Power of Ice in the Removal of Bowlders in Ponds. 



I am not aware that this phenomenon has been noticed on the east- 

 ern continent; and it has been but rarely observed on our own. Its 

 effects in modifying the face of the globe must be very limited ; yet 

 they deserve enumeration. 



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 removal of rock masses in this manner was first noticed in 

 Salisbury, Ct. ; and a statement published in Vol. 9th of the Amer- 

 ican Journal of Science. I have seen no similar instance in Massa- 

 chusetts ; but Rev. Sylvester Holmes, of New Bedford, informs me, 

 that an undoubted example of these traveling bowlders exists in a pond 

 in Carver, Plymouth County ; and that their track in the mud is 

 quite obvious. 



Action of the Sea upon the Coast. 



It would not be proper in this place to go into the minute details of 

 this subject. Where the combined and often conflicting agency of 

 breakers, tides, currents, and rivers at their mouths, is to be taken 

 into the account, it is obvious that very complicated effects must re- 

 sult : yet in general it may be stated, that the sea sometimes en- 

 croaches upon the land, and sometimes makes additions to it. Wheth- 

 er upon the whole these effects are balanced, is a question upon 

 which geologists are divided in opinion. My object is merely to 

 state such facts as have fallen under my notice in respect to the coast 

 of Massachusetts. 



Encroachments of the Sea. 



The most remarkable example of this occurs in Boston Harbor. 

 Here, as is well known, are numerous picturesque islands, the inner 



