1 909.] Ice on Canadian Lakes. 19 



ice, in other words, the viscosity of the ice must permit practically the 

 whole of the expansion with increase of temperature to act vertically. 



While the effect of horizontal expansion, if it occurred, would be 

 very great, the influence of expansion vertically has very little effect in 

 increasing the thickness of the ice. 



Now as the spring approaches, and the weather becomes bright and 

 warm, the ice begins to melt rapidly, at first around its edges close to the 

 shore where the heat from the sun, and also the heat rising from the earth 

 beneath the water, have the greatest combined effect. This melting of 

 the ice along the shore in the early spring loosens it from the sand, gravel 

 and rock so that it is no longer frozen tight to the beach, and consequently 

 it cannot then press the materials forming the shore back by expansive 

 force. The ice is then free from the shore, and is floating loosely on the 

 water, while the snow is melting on the surrounding country, and is dis- 

 charging a large quantity of water into the lake, which is rapidly rising in 

 consequence. From that time onwards until it melts away, the floating 

 ice is moved backwards and forwards on the surface of the water by the 

 varying winds. One day with a south wind, it may be drifted on the north 

 shore, while the next day the north wind may drive it with equal or greater 

 force on the south shore, and while it is pressed against the southern 

 shore there will be a lane of water between the ice and the land on the 

 north shore and vice versa. 



During the time in which the ice is driven backwards and forwards 

 by the varying winds for days and even weeks before it finally breaks up 

 and melts away, it is a very efficient instrument for ploughing up the 

 beach, since the force with which it is driven against the shore is almost 

 irresistible, and wherever it strikes against loose materials, such as sand, 

 gravel or boulders, it drives them back, and often piles them in a wall 

 behind the shelving beach. 



Dubawnt Lake, one of the large bodies of water out in the Barren 

 Lands of Northern Canada, is always more or less completely covered 

 with ice. In August 1893, when I was travelling in canoes through a 

 lane of water between the ice and the shore, the ice was sometimes several 

 hundred feet away from the land and at other times was tight up against 

 it. One night the ice was resting tight against the shore and we camped, 

 intending to portage across a long point of land in the morning, but on 

 the following morning, when we arose, the ice had withdrawn a hundred 

 feet or so from the shore and we were able to paddle easily and comfortably 

 around the point across which we had expected to have been obliged to 



