1909.] Ice on Canadian Lakes. 21 



straight shore shows clearly that they are caused by the irregular pressure 

 of broken ice in the spring, rather than by the regular expansion of the ice 

 during the winter with the variations of the temperature." 



"Behind this low beach is a wall of boulders that have been shoved 

 back against the higher ground within the edge of the woods, and have 

 reached their permanent resting place, where they can no longer be affected 

 to any considerable extent by the waves and ice of the present lake. 

 Within the woods is a ridge twenty feet high scattered with gneissoid 

 boulders."* 



The observations and conditions cited this evening establish the 

 following points, viz. : 



In regions of heavy snowfall the ice is being constantly pressed down 

 into the water by the weight of the snow, and therefore there is often 

 water over it and beneath the snow. 



In these regions the ice increases in thickness mostly from the top, by 

 the freezing of the overflowing water. 



In regions of light snowfall it increases in thickness mostly from the 

 bottom. 



It expands laterally with decrease in temperature, but most of the 

 expansion with increase in temperature is vertical. 



Throughout the winter, it remains firmly frozen to the shore, and 

 quite immovable, except that it falls with the lowering of the water in the 

 lakes. 



In the spring it thaws first along the shore, and around any stones, 

 etc., which attract the heat. 



The loose ice floating on the water of the main body of the lake in 

 spring is pushed against the shore by the wind, and sand and stones are 

 shoved up by and in front of it. 



These stones are often shoved in this way to the back of the beach 

 and are there piled into rough and heavy walls or ramparts. 



* Report on North Western Manitoba by J. B. Tyrrell, An. Rep. Geol. Sur. Can. 

 Vol. 1890-1, pp. 64-5 E., Ottawa Govt. 1893. 



