ICEBERGS. 677 



Glaciers, as these facts show, are also powerful agents in widening 

 and deepening valleys. 



The snow and ice of Alpine valleys often cause, indirectly, violent 

 erosion and transportation of material by damming up streams. 

 In no other way can barriers be thrown so readily across profound 

 valleys ; and the deluges caused by the accumulated waters when 

 they break loose are often very destructive. The Alps are full of 

 examples. 



4. ICEBERGS. 



A glacier on a sea-coast often stretches out its icy foot into the 

 ocean, and when this part is finally broken off by the movement 

 of the sea, or otherwise, it becomes an iceberg. Greenland is the 

 great region of icebergs, no less than of glaciers. They carry away 

 the stones and earth with which the glacier was covered during 

 its land-progress, and transport them often to distant regions, 

 whither they are borne by the polar oceanic currents. 



Dr. Kane describes the great pack of icebergs that occupies the 

 centre of Baffin's Bay, and mentions that some were 300 feet high, 

 and large numbers over 200 feet. There were 280 icebergs of the 

 first magnitude (the most of them over 250 feet) in sight at one 

 time. 



In the Antarctic, Captain Wilkes observed a long ice barrier, 

 having a height above the sea of 150 to 200 feet ; and some of the 

 bergs were 300 feet high. The ice of the barrier was stratified ; and, 

 according to Wilkes, this was owing to the constant increase from 

 the freezing mists over it. 



As the specific gravity of ice is 0.918 (at 32° F.), the proportion 

 of the mass out of water is about one-twelfth. 



The icebergs of the Atlantic melt mostly about the Banks of 

 Newfoundland, or between the meridians of 44° and 52°. They 

 have been observed in this ocean as far south as 36° 10'. 



Icebergs are (1) a means of transporting stones and earth from 

 one region to another (see p. 542). (2.) When grounded on rocks 

 they may scratch the surface; but closely-crowded and regular 

 scratches like those of glaciers over large areas could hardly be 

 made. The currents of Baffin's Bay flow southward on the west 

 side and northward on the other, — which would give great irre- 

 gularity there to the scratches of grounded bergs. An iceberg 

 " rocked by the swell of the sea, and sometimes turning over/' 

 could not be good at scoring submerged rocks. Moreover, these 

 rocks, in the seas in which icebergs melt and drop their freight of 

 stones, would seldom be uncovered. 



