OCEANOGRAPHY. 11 



the great oceans it is very deep. In the middle 

 of the North Sea, for example, we should not 

 expect to find a depth much exceeding 250 

 fathoms, but in the Atlantic or Pacific Oceans 

 we have to pay out more than 2000 fathoms of 

 the sounding line before the bottom is reached. 

 In some parts of the ocean-basins a few very 

 deep holes or furrows may be found in which 

 the depth exceeds 4000 fathoms, or 24,000 feet. 

 One of these deep holes occurs in the Atlantic 

 Ocean, a little to the North of the Virgin Islands 

 in the West Indies, and there is another in the 

 Pacific Ocean close to the coast of Japan ; but 

 the greatest depth that has yet been found is 

 one recently discovered by H.M.S. "Penguin" off 

 the coast of New Zealand of over 5000 fathoms. 

 Apart, however, from the fact that these very 

 great depths are only of local occurrence, the 

 areas of deep water that is, of more than 2000 

 fathoms are so much greater than the areas of 

 shallow water, that when we make a calculation 

 of the average depth of the sea we find it is no 

 less than 2100 fathoms, or 12,600 feet. 



The temperature of the sea is another feature 

 which undoubtedly influences very greatly the 

 character of its Fauna. The main source of the 

 heat of the sea is the sun for the heat derived 

 from submarine volcanoes must be comparatively 

 so small that we may omit it from consideration. 

 Consequently we find that in the Equatorial 

 regions the surface waters of the ocean are 

 warmer than they are in the Temperate regions. 

 These, again, are warmer than in the Arctic 

 circles. But water is well known to be a bad 



