DANGERS OF DISRUPTING ICE. 135 



which, -as they thicken, again unite, and are again 

 broken up into larger masses. These masses, by 

 rubbing against each other, have their edges slightly 

 rounded up, and in this form receive the name of 

 pancake ice. 



When a quantity of ice covers the ocean in a 

 wide level sheet of considerable extent, it is called 

 an ice-field. Fields of this kind are often seen by 

 navigators hundreds of miles in extent, and nearly 

 thirty feet thick. Ice of such thickness, however, 

 only shows five or six feet above water. When 

 fields are broken by heavy ocean-swells, the edges 

 are violently forced up, and fall in debris on the 

 surface ; thus hummocks or mounds are formed. 



When field-ice breaks up under the influence of 

 an ocean-swell, caused by a storm, the results are 

 terrific. 



An exceedingly graphic account of an incident of 

 this kind is given by Dr. Brown, in his " History 

 of the Propagation of Christianity." He writes : 



" The missionaries met a sledge with Esquimaux, 

 turning in from the sea, who threw out some hints- 

 that it might be as well for them to return. After 

 some time, their own Esquimaux hinted that there 

 was a ground-swell under the ice. It was then 

 scarcely perceptible, except on lying down and ap- 

 plying the ear close to the ice, when a hollow, dis- 

 agreeable, grating sound was heard ascending from 

 the abyss. As the motion of the sea under the ice 

 had grown more perceptible, they became alarmed, 



