124 SEA AND LAND 



its white color, become closed as the air escapes during the 

 onward journey of the stream. In more southern climes, as in 

 Norway and Switzerland, these crlaciers in their descent meet 

 a climate sufficiently \\*arm to melt them away before they 

 attain the level of the sea ; but in the greater part of the lands 

 within the Arctic Circle there is at the sea level an annual 

 average temperature below the freezing-point, so that any 

 glacier which is formed moves on until it thrusts its extremity 

 into the sea. 



For a time after the slow-movins: stream of ice enters the 

 ocean waters, its height causes it to continue to rest on the 

 bottom ; but when it penetrates to a certain depth of the sea, 

 a depth depending on the thickness of the ice-sheet, the buoy- 

 ing action brought about by the relative lightness of the ice 

 tends to lift it from the bed over which it has ploughed. As 

 ice, though easily mobile under pressure, as the movements of 

 the glaciers themselves clearly show, is very brittle to any 

 cross strain, such as this tendency to float imposes, the 

 extremity of the ice-stream is continuall)- broken away, form- 

 ing detachable masses. The resistance of the ice to fracture 

 causes the projecting extremity of the glacier to hold together 

 for a little distance beyond the point where the weight of the 

 mass alone would liold it upon the bottom. When the berg 

 separates from the parent mass, the rupture is attended by a 

 violent movement, often causino^ a loud thunderincr noise 

 which may be heard for many miles. The rebound of the 

 newly freed mass from the bottom and the firm-set glacier 

 whence it came, causes it to swing violently, so that it sends 

 great waves sweeping from its base out into the sea, which, 

 though on a larger scale, are like those produced when a ship 

 is launched. The Esquimaux are so familiar with this process 



