ICE PHENOMENA. 



417 



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 Ufted several feet from the shore, and then 

 pressed into the timbers forming the abutments of the bridge : as 

 shown in the preceding illustration, sketched on the spot. 



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 that I have witnessed at any one 

 time in a horizontal direction was six feet. This may be considered a 

 maximum shove. 



"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 •Aith. 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 precisely the reverse of this fractured 

 appearance. From my experience of ice I believe it is susceptible of 

 contraction, but to a very limited extent. I have witnessed many 

 sudden changes of temperature on Rice Lake, in some instances from 

 plus 30° to minus 20°, indicating a fall of some 50° ; and yet the 

 contraction of the ice, as made visible by open fissures, has not 

 exceeded three inches. 



I have repeatedly heard of openings, that have occurred during 

 former years, of several feet in width. I am inclined, however, to 

 believe, that the distinction between a shove and an open crack, or 

 fissure, was not sufficiently understood by my informants. 



