The Structure of the Atlantic : 27 



sea or other body of water may be very misleading as an index of its 

 inner character, depth and volume. Thus on a globe if we examine 

 the North Polar Seas (Arctic Mediterranean) we can see that they are 

 almost exactly three times the area of the Caribbean-Gulf System 

 (American Mediterranean); yet under the surface at least half of the 

 Polar waters are shallow and the American Mediterranean is nearly 

 all deep, so it holds more than half as much water as the Polar Med- 

 iterranean. Again the area of the Baltic is more than one-third the 

 area of Hudson Bay but it holds less than one-sixth as much water. 



Underwater the Polar Sea is an area of great contrast so we might 

 start our underwater glimpse of the Atlantic here. The deep part of 

 the Polar basin lies off the Alaskan coast and the adjacent coast of the 

 Canadian Arctic Islands and Greenland. It is egg-shaped with the 

 point of the egg aimed at Alaska. In this basin Sir Hubert Wilkins 

 obtained a sounding of 5,440 meters, or about 17,650 feet. Other 

 soundings give lower values but the basin is known to be deep par- 

 ticularly as contrasted to the areas off Siberia and Russia and that 

 north of Scandinavia. 



On the average a continental shelf is thirty miles wide but the seas 

 off Siberia are so wide and shallow that the continental shelf is as 

 much as 800 miles away from the coastline. 



There is an interesting point connected with these shallow north- 

 ern seas. It is generally recognized that the tides which we see along 

 our seacoast are the local evidences of two tidal waves on opposite 

 sides of the earth which sweep around the open oceans of the earth 

 every twenty-four hours and that these tidal waves are created by the 

 combined gravitational pull of the sun and the moon. 



As between the sun and the moon, the moon, though much 

 smaller, is so near to us that it plays the major part in creating the 

 tides as it circles around the earth. 



Astronomers and geophysicists have pointed out that this gravita- 

 tional pull is not a one-way street. While the moon is exerting a 

 force to move and drag the tides around the world, the tides in their 

 turn are exerting an equal hold and drag on the moon. It has recently 

 been calculated and pointed out that a large part of this drag, this 

 tidal friction, must be attributed to the shallow northern seas and 

 that they contribute somewhere between 70 per cent and 80 per cent 

 of this drag. 



One of the gateways into the Polar seas is the broad passage be- 

 tween the Shetland and the Faeroe Islands. Here we have an oppor- 

 tunity to illustrate how a feature on the bottom of the sea can influ- 



