THE NATIONAL GEOGRAPHIC MAGAZINE 



233 



THE DEPTH OP THE SEA AND HEIGHT OF" 

 THE LAND 



And yet so profound are the depths of 

 the sea that the bulk of the water in it 

 is fifteen times as great as the bulk of 

 the land that rises above its waves. In 

 its deepest trench the tallest mountain on 

 the face of the globe could be buried and 

 ships could still pass over the spot with a 

 half mile of water under them. 



The average depth of the ocean is more 

 than two miles — about 12,480 feet, the 

 oceanographers estimate. On the other 

 hand, the average height of the land is 

 less than half a mile — about 2,250 feet. 

 How much further beneath the waves the 

 sea bottom lies than the land crest above 

 them is shown by the fact that while only 

 one per cent of the land rises to an alti- 

 tude of 12,000 feet, 46 per cent of the 

 ocean's floor lies under more than 12,000 

 feet of water. 



The relative height of the land surface 

 and the sea bottom is about in keeping 

 with their relative areas, there being 71 

 acres occupied by the sea for every 29 

 held by the land. If it were possible to 

 drain off the upper 10,000 feet of the 

 waters of the sea and to lay bare the floor 

 that lies under it, the territory thus 

 recovered, added to the land now above 

 the sea, would give only a fifty-fifty di- 

 vision between land and water. 



THE CONTINENTAL SHEEP 



The oceans as we know them are larger 

 than the true ocean basin. As a monu- 

 ment is always planted on a base, so the 

 continents have broad under-sea bases 

 upon which to rest. To the oceanogra- 

 phers there is a line known as the 100- 

 fathom line, which largely parallels the 

 shore-line, but which is sometimes as 

 much as several hundred miles out to sea. 

 When that line is reached the bottom 

 suddenly begins to slope down toward the 

 abysmal depths. 



The floor lying landward from this line 

 is known as the continental shelf, and it 

 is upon this broad shelf, with an aggre- 

 gate area three times as large as that of 

 the United States, that the continents are 

 planted. By overflowing this vast area of 

 slightly submerged territory, the oceans 

 gather unto themselves ten million square 



miles of territory that in elevation be- 

 longs more to the land than to the sea. 



As a matter of fact, the continental 

 shelf lies in part under water and in part 

 above, the part above being the alluvial 

 plains of the continents. Where these 

 plains are broad the shelf usually is 

 broad, and where they are narrow the 

 shelf is usually narrow. For instance, 

 the plain on our Atlantic coast is broad, 

 and there is a corresponding breadth to 

 the continental shelf. On the Pacific 

 coast the alluvial plain is very narrow, 

 and the 100-fathom line is correspond- 

 ingly close to shore. 



WHAT THE CONTINENTAL, SHEEP COSTS 

 MANKIND 



From a practical standpoint, the part 

 of the sea of most immediate interest to 

 man is that which rests upon the conti- 

 nental shelf. Here are situated all the 

 seaboard cities. Wherever the ocean 

 lanes may meander up and down the 

 briny deep they begin on the continental 

 shelf and end there. But for that shelf 

 there would be no bays or gulfs, no har- 

 bors and no havens, for the boundaries of 

 the true ocean basins are infinitely more 

 regular and less indented than the shore- 

 lines. Ocean-bound commerce would be 

 vastly inconvenienced if it had to dispense 

 with all the advantages that the conti- 

 nental shelf brings to it. 



On the other hand, that shelf is a source 

 of much difficulty to shipping and of 

 much inconvenience to humanity. Upon 

 the ten million square miles of territory 

 upon which the sea has such a shallow 

 lien a population equal to that of Europe 

 and America might live. Aye, more than 

 that — it is all practically level, the recip- 

 ient of uncounted ages of rich contribu- 

 tions of fertility brought down by the 

 rivers from the land, and it might support 

 a population as dense as was that of Bel- 

 gium before the hob-nailed boot of Hun 

 warfare was set upon that smiling and 

 teeming land. 



Count the hundreds of millions of dol- 

 lars that the nations of the earth spend 

 on harbor dredging and coast-water sur- 

 veying; figure up the tremendous losses 

 of shipping tossed upon submerged rocks 

 by raging seas ; consider the losses in- 

 volved in the unending warfare between 



