74 THE WORLD'S LUMBER ROOM. 



from 50,000 to 100,000 tons, generally speaking, Arctic 

 bergs carry no load; and of the numerous icebergs 

 encountered by the Challenger in the Southern Seas as 

 many as forty being on one occasion, visible at once not 

 one in a thousand seemed to be carrying even mud. It 

 must be remembered, however, that but a small part of an 

 iceberg is visible, even when it consists of nothing but ice, 

 and the more heavily it is loaded the deeper it must float \ 

 besides which, large quantities of fragments, and even great 

 rocks, might be concealed in the upper part of the bergs by 

 the heavy falls of snow which they frequently receive after 

 setting out on their voyages. 



It is certain, however, that icebergs do act as "dust- 

 carriers," for besides the fact that gigantic boulders are at 

 times seen embedded in them, fragments of rock have been 

 dredged up from the bed of the ocean, which could have 

 been brought there only by floating ice. 



Besides the monsters to which some people would 

 restrict the term iceberg, there are other floating masses of 

 ice which vary from a few yards to a mile in circumference, 

 and sometimes far exceed these dimensions (Fig. 18). 



On the coast of Tierra del Fuego, where almost every 

 arm of the sea for 630 miles terminates in " tremendous 

 and astonishing glaciers," the crash which they make as 

 they break off into the sea, is like the " broadside of a 

 man o' war," and in Eyre's Sound Mr. Darwin saw as many 

 as fifty bergs floating away at once, one having a total 

 height of at least 168 feet, and some being loaded with 

 blocks of considerable size. In the southern seas, masses 

 of ice from a mile to seven or ten in length are met with, 



