NAVIGATION 293 



given later in the report. These observations show that the 

 thickness increases steadily until the month of June, when a 

 maximum of seventy-four inches was measured. The conditions 

 under which this was obtained were very favourable for the 

 ice, and only in similarly protected northern harbours does it 

 attain such a thickness. In the larger bays and along the un- 

 protected coasts, where the ice freezes later, and is frequently 

 broken up by gales during the winter, the thickness rarely 

 exceeds three or four feet. This thinner ice makes up the 

 greater part of that found in the spring-time covering the 

 waters of Hudson bay and strait. 



As the ice continues to increase until June, winter conditions 

 continue well into that month, and it is not until its last days 

 that the heat of the sun is sufficiently strong and sustained to 

 begin the melting process. With the advent of July this process 

 is well under way, and the daily change in the condition and 

 amount of the ice is then marvellous, so much so, that where 

 everything was fast frozen in the beginning of the month, by 

 the middle not a vestige of ice remains. 



If a single thickness of sheet ice covered these northern 

 waters they would be completely clear early in July, but unfor- 

 tunately much of the floating ice is ' rafted ' or piled up, sheet 

 on sheet, and the whole cemented solidly together to form large 

 masses often twenty feet or more in thickness. This rafting is 

 caused by the pressure formed by large masses of ice driven 

 together, or against ice attached to the shores, which causes the 

 ice along the margins to break and buckle, cake on cake. These 

 pressure areas are often of considerable size, and usually are 

 many times longer than broad. They serve as a framework to 

 hold together large fields of single sheet ice. When the thinner 

 ice melts, these pressure masses remain, and are dangerous to 

 shipping until the water has become sufficiently warm to melt 

 the ice cementing the cakes together; then they are harmless, 



