234 THE DEPTHS OF THE SE4. [CHAP. 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 when 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 off 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 Acores. Pico, 
the highest point of the Acores, is 7,613 feet (1,201 
fathoms) above the level of the sea, which gives from 
