PEPTH OF BLUE WA TER. 17 



to indicate the surface of a country in relief. The 

 curves are so drawn and stippled as to show distinctly 

 when the water is less than 6000 feet deep, when it 

 is less than 12,000 feet deep, when it is less than 

 18,000 feet, and when its depth lies between that and 

 24,000 feet. The conclusion is that the average 

 depth of blue water is not more than three or four 

 miles, and that no reliable soundings have been 

 made in water over five miles deep. This map (a 

 reduced copy of which is given opposite p. 28) gives 

 an idea, though an imperfect one, of tlie configura- 

 tion of the floor of the North Atlantic Ocean. 



The Mediterranean, the Black Sea, the Baltic, and 

 the seaboards of France and the British Isles, are 

 much better known. These seas are shallow com- 

 pared with the ocean, and the European marine 

 has too great an interest in their study to neglect 

 them. 



On the other hand, in the immense spaces left in the 

 southern hemisphere by the continents and islands of 

 Oceania the lead has rarely been thrown. The deep- 

 sea basins which separate Asia and Africa from 

 Australia and America have been but slightly ex- 

 plored, chiefly because the navigator there sails fear- 

 lessly before the wind, and dreads no rock or shoal 

 which would make him desirous of knowing the 

 depth of water on which he floats. Some obsorva- 



c 



