GLACIAL DRIFT. 313 
surface, in June. The ice had to be cut to enable the draught of water. 
In July, he found a mass of ice floating in this well as large as a wash- 
tub. 
In Plymouth, there is said to be an ice-cave in the west part of the 
town, where ice can be obtained every summer as late as the month of 
August. 
Upon the north slope of Green mountain in Effingham I found large 
masses of ice in the latter part of August, 1875. Near the edge of a 
precipice enormous blocks have been separated from the ledges, making 
large passages like caves, where different fragments rest upon each other 
like arches. On descending twenty feet I found ice, and then followed 
along forty feet to a much larger opening. This ice-cellar is well known 
to the people living in the neighborhood. 
A study of similar ice-masses elsewhere shows the existence of cur- 
rents of air, downward in the summer and upward in the winter, which 
evaporate the water, and, by the accompanying removal of heat, induce 
cold sufficient to freeze water and to preserve the ice thus formed. The 
principle has been made use of in warm countries to produce ice artifi- 
cially in merchantable quantities. 
BEAVER Dams. 
Several bogs in the state owe their existence to the former presence 
of the dams made by beaver. This animal is now entirely extinct, owing 
to the advance of clearings and the removal of the forests. It is not 
uncommon to find sticks that have been gnawed by these creatures. 
One such example is in Plainfield, where they occur underneath pine 
trees more than a foot in diameter. It is plain that here a bog was 
filled up by the natural accumulation of sediment in the beaver pond, 
and the land became dry enough for pines to grow. The name of 
“beaver meadow” is frequently heard throughout the state, and indi- 
cates the prevalence of bogs reclaimed by animal agency. One of the 
largest of these lies between Mts. Misery and Odiorne, in Weare, on the 
land of Hon. Moses Hodgdon, nearly a mile in length. It is-used for 
grass, and in wet seasons is often flooded with water. Logs occur quite 
deep down, in a soft mud in which poles can be thrust for several feet. 
