64 DYNAMICAL GEOLOGY. 



else by the falling of superglacial streams through great 

 fissures in the ice (crevasses) to the rocky bed below. 



Icebergs. 



We have already stated that in high-latitude regions 

 the lower limits of glaciers touch the sea. In South 

 America this occurs in 45 south latitude ; in Norway, in 

 65 north latitude ; and in Alaska, in 60 north latitude. 

 Still nearer the poles they run far into the sea, and by 

 the buoyant power of water, and the up-and-down move- 

 ment of tides and waves, are broken off in great prismatic 

 masses, and float away as icebergs. In the North Atlan- 

 tic the great source of icebergs is Greenland ; in the 

 Southern Ocean, the Antarctic Continent. 



Greenland. We have already said that Greenland is 

 completely covered with an ice-mantle 2,000 to 3,000 feet 

 thick, which moves bodily, by slow glacial motion, sea- 

 ward, producing doubtless universal erosion ; and divides 

 only at the margin into separate glaciers, which, running 

 through great fiords, thirty to forty miles long, into the 

 sea, there form icebergs. These are then taken by oceanic 

 currents and carried southward into warmer waters, where 

 they melt (Fig. 32). 



FIG. 32. Ideal section of a fiord and glacier, forming icebergs. /,/, sea level ; G, 

 glacier ; i, i, i, icebergs ; cl, cliffs. 



It is easy to see the necessity of this process. The 

 amount of snow which falls in polar regions is far greater 



