70 



AQUEOUS AGENCIES. 



Floating Ice — Icebergs. 



We have already seen (page 50) that at a certain latitude, varying 

 from 46° in South America to about 65° in Norway, glaciers touch the 

 surface of the ocean. Beyond this latitude, they run out to sea often to 

 great distances. By the buoyant power of water, assisted by tides and 

 waves, these projecting floating masses are broken off, and accumulate 

 as immense ice-barriers in polar seas, or are drifted away by currents 

 toward the equator. Such floating fragments of glaciers are called ice- 

 bergs. Fig. 65 is an ideal section, through a glacial valley, in which 

 a g is the glacier, b the cliffs beyond, I s' the sea-level, and i an iceberg. 



Formation of Icebergs. 



The principal source of the icebergs of the north Atlantic is the 

 coast of Greenland. This country is an elevated table-land, sloping 

 in every direction to a coast deeply indented like Norway, with alter- 

 nate deep fiords and jutting headlands. The whole table-land is com- 

 pletely covered with an ice-sheet, probably several thousand feet thick, 

 moving slowly seaward, and discharging through the fiords as immense 

 glaciers,* which, as already explained, form icebergs. In this remarka- 

 ble country no water falls from the atmosphere except in the form of 

 snow, and all the rivers are glaciers. The geological effects of such a 

 moving ice-sheet may be easily imagined. The whole surface of the 

 country rock must be polished and scored, the general direction of the 

 striae being parallel over large areas. 



The antarctic continent is probably similarly, and even more thick- 

 ly, ice-sheeted, for the humid atmosphere of that region is very favorable 

 to the accumulation of snow and ice. Captain Wilkes found an impen- 

 etrable ice-barrier, in many places 150 to 200 feet high, for 1,200 miles 

 along that coast. From this ice-barrier, icebergs separate and are drifted 

 toward the equator. 



* Dr. Rink, Archives des Sciences, vol. xxvii, p. 155. 



