540 



THE GEOLOGIST. 



It is observed on Rice Lake that the action of the mid -day sun will set the 

 glare ice immediately in motion. Warm winds, snow-storms, and rains, produce 

 the like eflFect, and the motion is perceptible. " It is not shrinkage nor contraction, 

 but, on the contrary, is a visible stretching and expanding of the lield-ice generally 

 towards the shore of the lake and of the islands," The movement of the ice is 

 sometimes gradual, accompanied by a slight crackling noise ; and sometimes the 

 expansion is rapid and violent, the movement being by a series of vigorous jerks, 

 accompanied by a hollow rumbling sound, seemingly from under the field-ice, 

 while at intervals there occur sharp loud reports, like those of cannon. 



That the ice does expand under such circumstances is evident, "as it may be 

 seen creeping many feet on to the shores, without the appearance in the lake of 

 any compensating fissures whatever." The force and violence with which the ice 

 expands or shoves, depends entirely on the extent of the change of the tempera- 

 ture ; and the most violent shoves of ice occur previous to rain-storms. A rise of 

 temperature of 20° and upwards produces violent expansion. The efifects of this 

 expansive power is evidenced in the railway-bridge before mentioned : — " Portions 

 of this structure on piles have been for long, distances bent and inclined, even to 

 an angle of 45°, in a most uniform and extraordinary manner — strong oak piles 

 that would not bend, have been cracked and splintered ; hundreds of heavy cap- 

 timbers of sound pine have been snapped across like reeds, and heavy iron rails 

 have been curved and doubled up by the almost irresistible pressure of the ice. 

 Instances of trees growing on the shores having been torn up by the roots are of 

 frequent occurrence. Large boulders, weighing two tons or more, have been lifted 

 several feet from the shore, and then pressed into the timbers of the abutments of 

 the bridge. Channels cut for the purpose of moving timber frequently close by 

 the expansion of the field-ice, and the timbers are heaved out high and dry." 



The greatest amount of expansion observed at any one time in an horizontal 

 direction was six feet ; and " when ice shoves on to the shores of lakes or islands, 

 it presents different forms of fracture according to the nature of the resistance it 

 meets with. Should the shore be low, the ice merely runs up and fractures at the 

 ripple -mark. On the contrary, should the ice meet with resistance from a vertical 

 shore or pier, a bursting up and piling of the fractured pieces would be the result." 



Ice, when contracting, presents the reverse of this fractured appearance, and, 

 according to Mr. Dumble, is susceptible of contraction to a very limited extent. 

 He says he has witnessed sudden depressions of temperature on Rice Lake of 50°, 

 *' and yet the contraction of the ice, as made visible by open fissures, has not 

 exceeded three inches." He thinks, however, that reported fissures of eighteen 

 inches may have happened. 



" When ice expands and is forced, perhaps, six feet on to the shore, should the 

 temperature again fall, this ice, which had previously exceeded its limits, does not 

 recede to its former position, neither will the main field separate over a few inches 

 from the fractured portions on the shore. On the contrary, should the temperature 

 again suddenly rise, a still further advance of perhaps the same distance is made 

 on to the shore." 



Such repeated expansions may occur many times during a winter, and yet little 

 evidence of any contraction will appear. Channels of six feet wide opened for the 

 purpose of isolating the Rice Lakes bridge, have been closed eight times within a 

 month by the expansion of the field-ice. An extraordinary instance of ice-piling 

 occurred on the embankment (twenty-six feet wide, and the rail on which is 



