(To be read before a Map)
IF the waters of the Atlantic could be drawn off, so as to expose to view the great trough which separates the Old World from the New, a scene would present itself of the grandest and most imposing character. The very ribs of the solid Earth, and the foundations of the hills, destitute of the garniture of vegetation, would be brought to light. We should have unrolled before us a vast panorama of mountains and valleys, of table- lands and plains, of deep gorges and lofty peaks, rivalling in grandeur and in variety the continents of the upper world.
Comparatively little is yet known of the bed of the South Atlantic; but the basin of the North Atlantic has been extensively surveyed by the English and American Navies. Let us suppose this vast basin to be emptied of its waters; and, with the aid of the charts which have been constructed, let us in imagination traverse these deep places of the Earth and learn what we can of their secrets. Remembering that what we have to explore is really a vast system of table-lands, mountains, and valleys, let us first endeavour to grasp its broad outstanding features.
In the northern part of the basin there stretches across the Atlantic from Newfoundland to Ireland a great submarine①plain, known in recent years as Telegraph Plateau.
About one
hundred miles from the coast of Ireland this plateau, rising as a broad terrace, reaches to within a hundred fathoms of the surface of the ocean. On this terrace stand the British Islands, the climate of which is materially affected by their being thus removed from the influence of the colder waters in the depths of the Atlantic. About midway between these islandsand Iceland, it has been found that icy cold water is constantly flowing towards the Equator, at a considerable depth beneath the surface, to supply the place of the warm surface-water moving northward from the Equator. At the depth of three- quarters of a mile, the temperature of this great polar current is two degrees below the freezing point. The British terrace raises these isles out of this cold stream, and thus none but the warmer upper waters flow around the British coasts.
From the middle of Telegraph Plateau an immense submarine continent, nearly as extensive as South America, stretches first southward and then towards the west, occupying the whole central area of the North Atlantic basin.
On either side of this central continent there is a broad and deep valley. These valleys converge as they go southward, and meet in mid-ocean between the Cape Verd and the West India Islands. Of these valleys, the western is much deeper than the eastern. Its deepest parts are found midway between the Bermudas and the Azores, and off the island of Porto Rico, where the sounding-line has been carried deeper than anywhere else in the ocean. It is the deepest part of the Atlantic.
Could we transport ourselves to that point, we should stand on what is perhaps the very lowest part of the Earth"s crust. We should be at least five miles below the ordinary level of the sea, surrounded on all sides by great mountains. On the north the Bermudas would be seen as lofty mountain-peaks, rising half as high again as the summits of the Alps or the Andes. On the north-east we should see the Azores as the culminating points of the central continent. Pico, their highest point, would appear, from the general level, as a mountain 400 feet②higher than Mont Blanc;but from our imaginary standpoint
in the lowest depths of the Atlantic, it would be six and a half miles in height-a mile higher than the highest peak of the Himalaya, the loftiest mountain on the globe.