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LESSON 4
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 submarine plain, 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 islands and 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 feet higher 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.
Each of these great ocean valleys rises in a series of terraces to the sides of the Old and New Worlds respectively. The course of the western valley, which lies off the United States and the West India Islands, has been traced as far south as to the Equator. The terraces of the eastern valley rise from the depths of the ocean to the western coasts of Europe and Africa. Off the coast of Africa they rise into a series of lofty and rugged summits, which we call Madeira, the Cape Verd, and the Canary Isles; and the whole system culminates in the Peak of Teneriffe in the last-named group. That peak is two miles and one-third above the level of the sea. The lowest point yet sounded in the bed of the Atlantic is five miles and a third below that level. The whole mountain system of the Atlantic basin, therefore, extends to upwards of seven miles in vertical height, or higher than any of the mountains of the globe are above the level of the sea.
By bringing up specimens from the depth of the Atlantic, and studying them under the microscope, it has been ascertained that the bed of the ocean is covered with very minute shells, which lie on the bottom as lightly as gossamer. The microscope has not detected a single particle of sand or gravel among these little mites of shells. This fact proves that quiet reigns in the depths of the sea: that as in the air ocean there is a region of perpetual calm, “above the clouds;” so in the ocean of waters there is a region where perpetual calm prevails, beneath the troubled waves. There is not motion enough to abrade these very delicate organisms, nor current enough to sweep them about, or to mix with them a grain of the finest sand.
It may be that the myriads of animalcules
which make the sea glow with life are secreting from it solid matter which is destined to fill up the cavities below. They furnish the atoms of which mountains are formed and plains are spread out. Our marl-beds, the clay in our river-bottoms, large portions of many of the great basins of the Earth, even flinty rocks, are composed of the remains of just such minute animals as those which have been fished up from a depth of three miles below the sea-level. These creatures, therefore, when living, may have been preparing the ingredients for the fruitful soil of a land that some earthquake or upheaval, in ages far away in the future, may yet raise up from the bottom of the sea for the use of man.
ascertained, found.
cavities, hollow places.
converge , draw near to each other.
culminating, crowning.
destined, appointed.
detected, discovered.
garniture, embellishment.
gossamer, cobweb.
ingredients, elements.
organisms, structures.
panorama, comprehensive view.
perpetual, constant.
separates, keeps apart.
submarine, under the sea.
summits, peaks.
surveyed, examined.
temperature, degree of heat.
transport, convey.
Of what does the bed of the ocean consist? What part of the Atlantic has been surveyed? By whom? What plain stretches across the northern part of the basin? On what do the British Isles stand? What effect has this on their climate? Why? What extends southward from the middle of Telegraph Plateau? What is there on either side of the central continent? Where is the deepest part of the Atlantic? If we could stand there, how far should we be below the sea-level? By what should we be surrounded? What would the Bermudas appear to be? And the Azores? Where does the whole Atlantic mountain system culminate? What is its extent in vertical height? With what is the bed of the ocean covered? What shows that quiet reigns in the depths of the sea? Of what are the animalcules found in the bed of the ocean the elements?