Page:Physical Geography of the Sea and its Meteorology.djvu/347

Rh conducts us into the very chambers of the deep. Our investigations go to show that the roaring waves and the mightiest billows of the ocean repose, not upon hard or troubled beds, but upon cushions of still water; that everywhere at the bottom of the deep sea the solid ribs of the earth are protected, as with a garment, from the abrading action of its currents, and that the cradle of its restless waves is lined by a stratum of water at rest, or so nearly at rest that it can neither wear nor move the lightest bit of drift that once lodges there.

596. The abrasion of currents.—The tooth of running water is very sharp. See how the Hudson has gnawed through the Highlands, and the Niagara cut its way through layer after layer of the solid rock. But what are the Hudson and the Niagara, with all the fresh water-courses of the world, by the side of the Gulf Stream and other great "rivers in the ocean?" And what is the pressure of fresh water upon river-beds in comparison with the pressure of ocean water upon the bottom of the deep sea? It is not so great by contrast as the gutters in the streets are to the cataract. Then why have not the currents of the sea worn its bottom away? Simply because they are not permitted to get down to it. Suppose the currents which we see at and near the surface of the ocean were permitted to extend all the way to the bottom in deep as well as shallow water, let us see what the pressure and scouring force would be where the sea is only 3000 fathoms deep—for in many places the depth is even greater than that. It is equal there, in round numbers, to the pressure of six hundred atmospheres. Six hundred atmospheres, piled up one above the other, would press upon every square foot of solid matter beneath the pile with the weight of 1,296,000 pounds, or 648 tons.

597. Their pressure on the bottom.—The better to comprehend the amount of such a pressure, let us imagine a column of water just one foot square, where the sea is 3000 fathoms deep, to be frozen from the top to the bottom, and that we could then, with the aid of some mighty magician, haul this shaft of ice up, and stand it on one end for inspection and examination. It would be 18,000 feet high; the pressure on its pedestal would be more than a million and a quarter of pounds; and if placed on a ship of 648 tons burden, it would be heavy enough to sink her. There are currents in the sea where it is 3000 fathoms deep, and some of them—as the Gulf Stream—run with a velocity of four miles