ALLUVIAL DIVISION. 
41 
Blocks transported hy Ice. 
Bigsby, in describing the geology of Lake Huron, remarks, 
“ In the spring, the ice removes fragments of great size. In the winter it surrounds those which are 
placed in the shallows; and on being broken up hy the mild weather of spring, by the rise of water 
which takes place in consequence of the blowing of the wind, they are either carried higher on the 
shore, leaving a furrow behind them, or they are moved oiF with the field of ice to which they are 
attached, and on the melting of the ice, deposited on some other shore more or less distant from their 
original situation. Rounded rocks of some yards in diameter, are thus removed.”* 
“ There is a curiosity to be seen in the Long pond in Bridgeton. In a cove on the east side of the 
pond, the water is so shoal that a man may wade fifty rods into it. On the bottom of this cove are many 
stones of various sizes, which have an evident annual motion towards the shore. The proof of this is, 
the tracks or furrows left behind them, and the clay driven up before them. Some of the stones are two 
or three tons weight, have left a track several rods behind them, and have at least a cartload of clay piled 
up before them. Some of them are covered with water all the year. The shore of the cove is lined 
with these stones three feet deep, which, it would seem, have crawled out of the water.” t 
Similar facts have been observed in Salisbury in Connecticut, and other places and by 
attentive observation, may be seen in many of the small lakes in New-York. 
Explanation of the cause. The explanation of this fact is, that in the winter the rocks 
are enclosed in thick firm ice, which in freezing expands from the centre towards the shores, 
thrusting the rocks along with a powerful force, ploughing the earth up before it, and leaving 
a corresponding furrow behind. Another and principal cause is, that when the ice begins to 
thaw in the spring, the powerful winds elevate the waters rather above their usual level on the 
leeward side ; thus, the ice lifts the enclosed rocks, and the wind drifting it towards the shore, 
produces the same effect as in the other case. The ice thaws first around the shores of ponds, 
and is thus anchored by means of its attached rocks, and the winds cause it to drag the stones 
along the bottom. 
Another cause of these effects is, by the thawing of the snow during the spring and latter 
part of winter, much surface water finds its way into the lake, and its surface is raised some 
inches or feet above its usual level. The ice continuing to float, raises or buoys up such 
masses of rock as are not too firmly fixed, or too heavy to be sustained by the strength of the 
ice, and floated off; and when they ground, they plough up the earth before them, and leave 
a furrow behind. 
Ground Ice. 
The ice called ground ice, is also a powerful means of transport for blocks, pebbles, gravel 
and sand. It forms in water during cold weather, at the bottoms of streams and lakes ; and 
* American. Jour, of Science, Vol. 3, p. 256. t Collections of Mass. Hist. Society, Vol. 3, p. 240. 
t Am. Jour, of Science, Vol. 5, p. 34; Vol. 9, p. 136. Dwight’s Travels, Vol, 5, p. 34. 
Geol. 1st Dist. 6 
