402 METEOROLOGY. 



Ice exhibits other phenomena not generally noticed, an account of 

 some of which may be interesting. Ice, as is well known, expands in 

 freezing ; but when once frozen, is governed by the same laws as all 

 other solid bodies. Its alternate contraction and expansion produces 

 the same effect of motion upon the ice of our frozen ponds and rivers 

 as is produced by similar causes upon the glaciers of Switzerland. The 

 first increase of cold, after they are frozen, causes the ice to contract 

 and crack with a loud report. These cracks are generally only super- 

 ficial, but always extend from shore to shore. A mild day expands 

 the ice, and at the same time fills these cracks with water, which 

 freezing, still further enlarging the mass, causes it to press with great 

 force upon the shore, tearing up the ground, and heaving the ice into 

 high ridges. Once at the north end of Winthrop pond, which is nine 

 miles in length, and should be called a lake, I saw a tree fifteen or six- 

 teen inches in diameter, which had been forced up by the roots, and 

 removed by the ice several feet from the place of its original growth. 

 The ebbing and flowing of the tide tends still further to increase the 

 ridges on Kennebec river ; for the ice on the flats remains stationary, 

 while the channel ice separates from it as the tide ebbs ; and when the 

 tide flows again, the space is filled with water to be frozen, still in- 

 creasing the mass and enlarging the ridges which are formed between 

 the flats and the channel ice. The ridges are not uniform on the two 

 sides of the river, but are always highest where the pressure of the 

 current is greatest ; and wherever there are roads on to the river, these 

 ridges have to be cut down and bridged over with timber and plank. 

 The ridges thrown up on Moose Head lake, the source of Kennebec 

 river, are much more remarkable. The following account of them is 

 -derived principally from a person of veracity, who has spent eighteen 

 winters encamped on one of the islands in the lake, surveying the logs 

 scut on its margin to be floated to the mills below. His account is 

 .confirmed by other persons whose business has led them to spend a 

 few days every winter on the lake. Upon the first thaw after the lake 

 is frozen, and which usually occurs early in January, ridges are thrown 

 up across the lake with a very loud report, compared by some persons 

 to an earthquake, by others to very loud thunder. Owing to the 

 precipitous character of the shores o£ the lake, these ridges are not 

 formed, as in our ponds, on its margin, but across the lake, and always 

 extend from shore to shore. The two principal ridges are formed from 

 year to year from the same points. Smaller ridges appear in other 

 places. These ridges are never thrown up in severely cold weather, 

 but during, or immediately after, a thaw. As the season advances 

 they increase in height till they sometimes rise eight or ten feet above 

 the surface of the lake, and have to be cut down to admit passing over 

 them. Towards the close of winter they become weakened by the 

 mild weather, and sink into the lake, where they are dissolved, leaving 

 an open space across the lake from fifteen to twenty feet in width, and 

 which the lumber men are obliged to cross in boats. The person above 

 referred to told me of another singular circumstance; that a strong 

 wind raises the water at the end to which it blows, as high when the 

 lake is covered with ice as when it is free from it. This seemed to me 

 so remarkable, that I questioned my informant how he knew this to 



