146 DISPERSION OF ERRATICS. [Ch. XI. 



and floor of the ocean, which is now one of subsidence, but which 

 may at some future time be converted into one of upheaval, we are 

 presented with a key to the interpretation of many distinct classes of 

 glacial phenomena once regarded as most enigmatical. 



An account was given so long ago as the year 1822, by Scoresby, 

 of icebergs seen by him in the Arctic seas drifting along in latitudes 

 69° and 70° INT., which rose above the surface from 100 to 200 feet, 

 and some of which measured a mile in circumference. Many of 

 them were loaded with beds of earth and rock, of such thickness that 

 the weight was conjectured to be from 50,000 to 100,000 tons. A 

 similar transportation of rocks is known to be in progress in the 

 southern hemisphere, where boulders included in ice are far more 

 frequent than in the north. One of these icebergs was encountered 

 in 1839, in mid-ocean, in the antarctic regions, many hundred miles 

 from any known land, sailing northward, with a large erratic block 

 firmly frozen into it. In order to understand in what manner long 

 and straight grooves may be cut by such agency, we must remember 

 that these floating islands of ice have a singular steadiness of motion, 

 in consequence of the larger portion of their bulk being sunk deep 

 under water, so that they are not perceptibly moved by the winds 

 and waves even in the strongest gales. . Many had supposed that the 

 magnitude commonly attributed to icebergs by unscientific navigators 

 was exaggerated, but now it appears that the popular estimate of 

 their dimensions has rather fallen within than beyond the truth. 

 Many of them, carefully measured by the officers of the French explor- 

 ing expedition of the Astrolabe, were between 100 and 225 feet high 

 above water, and from two to five miles in length. Captain d'TJrville 

 ascertained one of them which he saw floating in the Southern Ocean 

 to be 13 miles long and 100 feet high,, with walls perfectly vertical. 

 The submerged portions of such islands must, according to the 

 weight of ice relatively to sea-water, be from six to eight times more 

 considerable than the part which is visible, so that when they are 

 once fairly set in motion, the mechanical force which they might exert 

 against any obstacle standing in their way would be prodigious.* 

 A considerable proportion of these floating masses of ice is supposed 

 not to be derived from terrestrial glaciers, but to be formed at the foot 

 of cliffs by the drifting of snow from the land over the frozen surface 

 of the sea, the snow by repeated melting and regelation being in 

 time converted into ice. But most of the bergs of the Southern 

 Ocean are formed in the same way as the principal ones in Baffin's 

 Bay ; for Dr. Hooker informs me that the ice of the Antarctic Con- 

 tinent, or Victoria Land, like that of Greenland, as described by Rink, 

 is strewed over with rocky fragments, there being always some bare 

 precipices and mountain peaks protruding from the great wilderness 

 of snow from which moraines may be derived. These moraines are 



* T. L. Hayes, Boston Journ. Nat. Hist., 1844. 



