234 TEE DEPTHS OF THE SEJ. [cHAr. v. 



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 1,700 fathoms at the 

 rate of about fifteen to nineteen feet in the 100 ; 

 and from this point to within about 200 miles of 

 the coast of Newfoundland Avhen it begins to shoal 

 again, there is a vast undulating submarine plain, 

 averaging about 2,000 fathoms in depth below the 

 surface — the ' telegraph plateau.' 



A valley about 500 miles wide, and with a mean 

 depth of 2,500 fathoms, stretches from oflp the south- 

 west coast of Ireland, along the coast of Europe 

 dipping into the Bay of Biscay, past the Strait of 

 Gibraltar, and along the west coast of Africa. Oppo- 

 site the Cape de Verde Islands it seems to merge into 

 a slightly deeper trough, which occupies the axis of 

 the South Atlantic and passes into the Antarctic Sea. 

 A nearly similar valley curves round the coast of 

 North America, about 2,000 fathoms in depth off 

 Newfoundland and Labrador, and becoming consider- 

 ably deeper to the southward ; where it follows the 

 outline of the coast of the States and the Bahamas 

 and Windward Islands, and finally joins the central 

 trough of the South Atlantic off the coast of Brazil, 

 with a depth of 2,500 fathoms. A wide nearly level 

 elevated tract with a mean depth below the surface 

 of 1,500 fathoms, nearly equal in area to the con- 

 tinent of Africa, extends southwards from Iceland as 

 far as the 20th parallel of north latitude. This 

 plateau culminates at the parallel of 40° north 

 latitude in the volcanic group of the i\cores. Pico, 

 the highest point of the Acores, is 7,63 3 feet (1,201 

 fathoms) above the le-\^el of the sea, \A'hich gi\ es from 



