254 OUR HERITAGE THE SEA 



called a berg, since the submerged portion of an ice- 

 berg, owing to the slight difference between the specific 

 gravity of ice and water, is about eight times as deep 

 as that appearing above water is high. One valuable 

 result from this is that the navigation of the North 

 Pacific is not impeded by the presence of these wander- 

 ing dangers, which constitute the most terrible of all 

 mid-ocean perils for the seafarer. Another great pecu- 

 liarity of the Pacific is the vast number of scattered 

 island groups, nearly all of which are mainly of coral, 

 although the evidences of submarine volcanic energy 

 are very frequent, the appearance or disappearance of 

 islets in a day being of such frequent occurrence as 

 to constitute a considerable danger in navigating those 

 intricate waters. 



It is notable, too, for its immensely greater average 

 depth than that of the other oceans, although, knowing 

 what we do of the immense depths that have been 

 discovered within comparatively small areas surrounded 

 by much shallower waters, it is far too much" to say 

 that even the great deeps that have been plumbed 

 are the deepest that will be found. Many years of 

 incessant labour in deep-sea sounding, even with the 

 present splendid instruments used for that purpose, 

 must elapse before we are in a position to say we know 

 exactly how deep the ocean is, if, indeed, we ever do 

 know. Besides, it must be remembered that this is a 

 scientific question, not a commercial one at all, a depth 

 sufficient to float the biggest ship we can build, with a 

 fair margin over so that the heaviest seas may not 

 break, being amply sufficient for all navigational 

 purposes. 



Yes, the Pacific, besides being the most vast in 



