8 PHYSICAL GEOGRAPHY OF THE SEA. 



there is only one very marked mass of mountains, the volcanic 

 group of the Acores." 



Accurate soundings are as yet much too distant to justify 

 a detailed description of the bed of the Atlantic. I will merely 

 state that after sloping gradually to a depth of 500 fathoms to 

 the westward of the coast of Ireland, in lat. 52° N., the bottom 

 suddenly dips to 1700 fathoms, at the rate of from about 15 to 

 1 9 feet in the 100. From this point to within about 200 

 miles of the coast of Newfoundland, where it begins to shoal 

 again, there is a vast undulating plain averaging about 2000 

 fathoms in depth below the surface — the " telegraph plateau ' 

 on which now rest the cables through which the electric power 

 transmits its marvellous messages from one world to another. 



Our information about the beds of the Indian, the Antarctic, 

 and the Pacific Oceans is still more incomplete, but the few 

 trustworthy observations which have hitherto been made seem 

 to indicate that neither the depth nor the nature of the bottom 

 of these seas differs greatly from what we find nearer home. 



The inclosed and landlocked European seas are very shallow 

 when compared with the high ocean : the Mediterranean, how- 

 ever, has in some parts a depth of more than 6000 feet ; and 

 even in the Black Sea, the plummet sometimes descends to 

 more than 3000 feet ; while the waters of the Adriatic every- 

 where roll over a shallow bed. 



The researches of Mr. Kussell on the swiftness of the tide-wave, 

 showing that the rapidity of its progress increases with the 

 depth of the waters over which it passes, afford us another means, 

 besides the sounding line, of determining approximately the 

 distance of the sea-bottom from its surface. According to this 

 method, the depth of the Channel between Plymouth and 

 Boulogne has been calculated at 180 feet; and the enormous 

 rapidity of the flood wave over the great open seas (300 miles 

 an hour and more) gives us for the mean depth of the Atlantic 

 14,400 feet, and for that of the Pacific 19,500. 



Natural philosophers have endeavoured to calculate the 

 quantity of the waters contained within the vast bosom of the 

 ocean ; but as we are still very far from accurately knowing the 

 mean depth of the sea, such estimates are evidently based upon 

 a very unsubstantial foundation. 



So much at least is certain, that the volume of the waters of 



