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.
The researches of Mr. Russell 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 the ocean as much surpasses all conception, as the number of their inhabitants, or of the sands that line their shores.
Torso Rock, near Point Deas Thomson, in the Arctic Ocean.
The boundaries of the ocean are not invariable; while in some parts it encroaches upon the land, in others it retreats from the expanding coast. In many places we find the sea perpetually gnawing and undermining cliffs and rocks; and sometimes swelling with sudden rage, it devours a broad expanse of plain, and changes fertile meads into a dreary waste of waters. The Goodwin Sands, notorious for the loss of many a noble vessel, were once a large tract of low ground belonging to Earl Goodwin, father of Harold, the last of our Saxon kings; and being afterwards enjoyed by the monastery of St. Augustine at Canterbury, the whole surface was drowned by the abbot's neglect to repair the wall which defended it from the sea. In spite of the endeavours of the Dutch to protect their flat land by dykes against the inundatory waters, the storm-flood has more than once burst through these artificial boundaries, and converted large districts into inland seas.