THE POLAK SEAS. 57 



Hummocks form themselves of the stray, broken icebergs which come 

 in contact with each other at their edges, and thus form vast rafts, 

 the pieces of which may exceed a hundred yards in length. 



When these icebergs are separated by open spaces, through which 

 vessels can be navigated, the pack ice is said to be open. But it often 

 happens that mountains of ice occur partly submerged, where one 

 edge is retained under the principal mass, while the other is above the 

 water. Scoresby once passed over a calf, as English mariners call 

 these icy mountains, but he trembled while he did so, dreading lest it 

 should throw his vessel, himself, and crew into the air before he could 

 pass it. The aspect of the ice-fields varies in a thousand ways. Here 

 it is an incoherent chaos resembling some volcanic rocks, with crevices 

 in all directions, bristling with unshapely blocks piled up at random ; 

 there it is a strongly-marked plain, an immense mosaic formed of vast 

 blocks of ice of every age and thickness, the divisions of which are 

 marked by long ridges of the most irregular forms ; sometimes re- 

 sembling walls composed of great rectangular blocks, sometimes re- 

 sembling chains of hills, with great rounded summits. 



In the spring, when a thaw sets in, and the fields begin to break up, 

 the pieces of light ice which unite the great blocks into unique masses 

 are the first to melt ; the several blocks then separate, and the motion 

 of the water soon disperses them, and the imprisoned ships find a free 

 passage. But a day of calm is still sufficient to unite the dispersed 

 masses, which oscillate and grind against each other with a strange 

 noise, which sailors compare to the yelping of young dogs. 



When a ship is shut up in one of these floating ice-fields, inexpli- 

 cable changes sometimes occur in the vast incoherent aggregations. 

 Vessels, which think themselves immovable, are found in a few hours to 

 have completely reversed their positions. Two ships shut in at a 

 short distance from each other were driven many leagues without 

 being able to perceive any change in the surrounding ice. At other 

 times ships are drawn with the floating ice-fields, like the white bears, 

 who make long voyages at sea upon these monster vehicles. In 1777 

 the Dutch vessel, the Wilhelmina, was driven with some other whaling 

 ships from eighty degrees north back to sixty-two degrees, in sight of 

 the Iceland coast. During this terrible journey the ships were broken 

 up one after the other. More than two hundred persons perished, 

 and the remainder reached land with difficulty. 



