"The general result," says Professor Wyville Thomson,[A] "to which we are led by the careful and systematic deep-sea soundings which have been undertaken of late years is that the depth of the sea is not so great as was at one time supposed, and does not appear to average more than 2000 fathoms (12,000 feet), about equal to the mean height of the elevated table-lands of Asia.
[Footnote A: "The Depths of the Sea," p. 228.]
"The thin shell of water which covers so much of the face of the earth occupies all the broad general depressions in its crust, and it is only limited by the more abrupt prominences which project above its surface, as masses of land with their crowning plateaux and mountain ranges. The Atlantic Ocean covers 30,000,000 of square miles, and the Arctic Sea 3,000,000, and taken together they almost exactly equal the united areas of Europe, Asia, and Africa--the whole of the Old World--and yet there seem to be few depressions on its bed to a greater depth than 15,000 or 20,000 feet--a little more than the height of Mont Blanc; and, except in the neighbourhood of the shores, there is only one very marked mass of mountains, the volcanic group of the Açores."
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 19 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 land-locked European seas are very shallow when compared with the high ocean: the Mediterranean, however, 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 everywhere roll over a shallow bed.