TERRESTRIAL HEAT. 



and suddenly congealed. These stupendous arches, however, do 

 not always possess cohesion in proportion to their weight, and 

 after augmenting in volume to a certain limit, sink under their 

 weight, and, breaking with a terrific crash, fall into the sea. 



45. The depth of the seas off the coast of Greenland is not con- 

 siderable. Whales, being harpooned, often plunge in their agony 

 to the bottom, carrying with them the harpoon and line attached 

 to it. "When they float they bear upon their bodies evidence of 

 having reached the bottom by the impression they retain of it, 

 and the length of line they carry with them in such cases shows 

 that depth does not exceed 3000 or 4000 feet. About the middle 

 of the space between Spitzbergen and Greenland the soundings 

 have reached 8000 feet without finding bottom. 



46. The degree of cold of the polar regions, like the temperature 

 of all other parts of the globe, depends on the extent and depth of 

 the seas. If there be extensive tracts of surface not covered by 

 water, or covered only by a small depth, the influence of the 

 water in moderating and equalising the temperature is greatly 

 diminished. Hence it is that the temperature of the south polar 

 regions is more moderate than that of the north. After passing 

 the latitude of the New Orcades and the New Shetlands, which 

 form a barrier of ice, the navigator enters an open sea, which, 

 according to all appearance, extends to the pole. Much, however, 

 still remains to be discovered respecting the physical condition of 

 these regions. 



