DERELICTS AND ICEBERGS 53 



claim that sudden changes of temperature 

 mean nothing so far as ice is concerned. In 

 many cases they found no change in the tem- 

 perature of the water up to within a ship's 

 length of bergs, whereas the coldest water they 

 found was one hundred miles from the nearest 

 ice. Even close to a berg the temperature of 

 the water falls only from two to four degrees. 

 Flocks of birds sometimes indicate the near- 

 ness of ice, but, unless one is familiar with the 

 species of birds, their absence or abundance 

 can not be depended upon to prove bergs near 

 at hand, for on the fishing banks one often 

 sees, far from ice, large flocks of various sea- 

 birds which have been attracted by the fish- 

 ing vessels. The only sure way of navigating 

 in safety in those seas where bergs are liable 

 to be met is to proceed very slowly and cau- 

 tiously and to use all the known means of locat- 

 ing ice without depending too much on any 

 one method, especially in thick weather. All 

 icebergs are formed in the far Arctic or Ant- 

 arctic, where glaciers fill the deep valleys and 

 fjords that lead inland from the sea. As these 

 glaciers move slowly — like great frozen rivers 



