48 



THE POLAR WORLD. 



FORMS OF ICEBEUGS. 



wiiieli may possibly be revolving with equal rajjidity in an opposite direction 

 —when masses not seldom twenty or thirty miles in diameter, and each weigh- 



ing many millions of tons, clash to- 

 gether, imagination can hardly con- 

 ceive a more appalling scene. The 

 whalers at all times recpiire unremit- 

 ting vigilance to secure their safety, 

 but scarcely in any situation so much 

 as when navigating amidst these 

 fields, which are more pai'ticularly 

 dangerous in foggy weather, as their 

 motions can not then be distinctly ob- 

 served. No wonder that since the 

 establishment of the fishery numbers 

 of vessels have been crushed to pieces 

 between two fields in motion, for the 

 strongest shij:) ever built must needs 

 be utterly unable to resist their power. Some have been uplifted and thrown 

 upon the ice; some have had their hulls completely torn open; and others 

 have been overrun by the ice, and buried beneath the fragments piled upon 

 their wreck. 



The icebergs, which, as their name 

 indicates, rise above the water to a 

 much more considerable lieight than 

 the ice-fields, have a very different or- 

 igin, as they are not formed in the 

 sea itself, but by the glaciers of the 

 northern highlands. As our rivers 

 are continually })ouring their streams 

 into the ocean, so many of the gla- 

 ciers or ice-rivers of the Arctic zone, 

 descending to the water-edge, are 

 slowly but constantly forcing them- 

 selves farther and farther into the 

 sea. In the summer season, when 

 the ice is particularly fragile, the 

 force of cohesion is often overcome 

 by the weight of the prodigious mass- 

 es that overhang the sea or have been 

 undermine«l by its waters ; and in the 

 winter, when the air is probably 40° 

 or 50° below zero and the sea from 

 28° to 30° above, the unequal expan- 

 sion of those ])arts of the mass ex- 

 I>osed to so great a difference of temperature can not fail to produce the sep- 

 aration of large portions. 



? 



FOKMS OF ICEBERGS. 



