SEA WATER 



Ice 



241 



In the polar regions the surface of the sea is frozen. 

 When the surface water freezes it does not usually attain 

 a greater thickness than seven feet in a year. When first 

 formed it is known as " floe ice " (Plate 84). Cracks in 

 the ice, widening into lanes, cause the separation of the 

 ice into floes which drift at the mercy of wind and current. 

 Under certain conditions these floes become driven together 

 and under the great pressure they become packed together 

 to form a mass with uneven surface, floes becoming tilted 

 up on end and forced half out of the water, the whole 

 presenting an appearance of jumble and disorder. Such 

 ice is known as " pack ice " (Plate 84). 



In the open ocean, often far from polar regions, " ice- 

 bergs " are met with (Plate 86). These are in no way 

 connected with the floe or pack ice, but are derived from 

 glaciers. The majority of those met with in the North 

 Atlantic come from the great glaciers of Greenland. These 

 solid rivers of ice flow slowly into the sea, where partly 

 by wave action, and partly by uneven adjustments of 

 weight, great masses break off to form the icebergs. 

 The actual process of breaking off is known as the " calving 

 of an iceberg." 



These castles of ice, often fantastic in shape, float down 

 into the Atlantic on the Labrador Current, a menace to 

 passing shipping. Only a small portion of the mass of ice 

 is visible above water, as it floats with almost eight-ninths 

 submerged. 



Recently a new method has been tried for destroying these 

 floating perils. A boring is made into the side of the berg 

 and a charge of " thermite " inserted, which, on ignition, 

 gives off an intense heat. After several hours the berg 

 breaks up owing to the uneven stresses and strains set up 



