1909.] Ice on Canadian Lakes. 17 



of ten or twelve inches, from four to six inches of the lower part of the snow 

 was soaked with water. Shortly after the snow storm very cold weather 

 set in and this wet snow was frozen to ice, and thus the general thickness 

 of the ice was greatly increased by freezing from above and not from below. 



Later in the winter the weight of snow would again become too great 

 for the buoyancy of the ice and would press it down into the water, which 

 would rise through and over it and cover it, possibly to a depth of a foot 

 or more, with watery slush. The surface of this slush might be again 

 frozen during the spells of extremely cold weather which occur in the 

 latter part of the winter. In this way two sheets of ice might be formed, 

 separated by a foot or more of water and slush. These two thicknesses 

 are very commonly found on our northern lakes in the latter part of the 

 winter and a man or team of horses may break through the upper and still 

 be supported by the lower layer. Instead of freezing and forming a second 

 upper thickness of ice, the water may melt the snow and carry it off 

 the surface or down again beneath the ice. Thus relieved of its load of 

 snow and slush, the ice will again float to the surface and may become quite 

 dry and hard. The formation of this dry, hard ice just at the approach 

 of spring, after it has been very wet and sloppy for some weeks, is a con- 

 dition that is well known to lumbermen and others who have occasion to 

 travel in the north. 



In regions where the snowfall is light, a sudden fall in the tem- 

 perature of the air will have considerable effect in increasing the thickness 

 of the ice. While the cold weather causes the ice to thicken, it also causes 

 it to contract, for as stated above, ice has a fairly high coefficient of ex- 

 pansion, and si change of one degree F. in temperature causes it to expand 

 or contract to the extent of about two or three inches in a mile. In ex- 

 tremely cold nights this contraction often causes extensive cracks or fissures, 

 which are formed with the accompaniment of loud reports so that the 

 booming of the ice, while these fissures are forming on the larger lakes in 

 the north, can often be heard for many miles. The fissures usually cross 

 a lake in the same place each year, probably between salient points on the 

 shores, and give rise to lanes of open water. On Lake Winnipeg these 

 stretches of open water often cause obstructions in the ice roads which 

 are used in teaming from place to place over the lake. 



Now as it is quite clear that these fissures are formed by the con- 

 traction of the ice with the lowering of the temperature it was reasonable 

 to infer that the ice would expand again horizontally when its temperature 

 was raised. The fissures formed by contraction freeze over quickly in the 

 cold weather and as the temperature rises the ice expands and closes 



