134 THE FOKMS OF WATEK IN 



in 500 feet of water. This would make tlie entire 

 height of the berg 750 feet, not an unusual altitude for 

 the greater icebergs. 



344. From Baffin's Bay these mighty masses come 

 sailing down through Davis' Straits into the broad 

 Atlantic. A vast amount of heat is demanded for the 

 simple liquefaction of ice (§ 48) ; and the melting of 

 icebergs is on this account so slow, that when large 

 they sometimes maintain themselves till they have been 

 drifted 2000 miles from their place of birth. 



345. What is their origin? The Arctic glaciers. 

 From the mountains in the interior the indurated snows 

 slide into the valleys and fill them with ice. The 

 glaciers thus formed move like the Swiss ones, inces- 

 santly downward. But the Arctic glaciers reach the 

 sea, enter it, often ploughing up its bottom into sub- 

 marine moraines. Undermined by 1he lapping of the 

 waves, and unable to resist the strain imposed by their 

 own weight, they break across, and discharge vast 

 masses into the ocean. Some of these run aground on 

 the adjacent shores, and often maintain themselves for 

 years. Others escape southward, to be finally dissolved 

 in the warm waters of the Atlantic. The first engra- 

 ving on the opposite page is copied from a photograph 

 taken by Mr. Bradford during a recent expedition to the 

 Northern seas. The second represents a mass of ice 

 upon the Glacier des Bossons. Their likeness suggests 

 their common origin. 



