Page:Physical Geography of the Sea and its Meteorology.djvu/349

Rh how strong, how light yet how firm are the foundations of the sea! Its waves cannot fret them, its currents cannot wear them, for the bed of the deep sea is protected from abrasion by a cushion of still and heavy water. There it lies—that beautiful arrangement—spread out over the bottom of the deep, and covering its foundations as with a garment, so that they may not be worn. If the currents chafe upon it now here, now there, as in shallow seas they sometimes do, this protecting cushion is self-adjusting; and the moment the unwonted pressure is removed the liquid cushion is restored, and there is again compensation.

600. The causes that produce currents in the sea reside near its surface.—The discovery of this arrangement in the oceanic machinery suggests that the streams of running water in the sea play rather about its surface than in its depths; that the causes which produce currents reside at and near the surface; that these causes are changing heat and alternating cold with their powers of contraction and expansion—winds and sea-shells with evaporation and precipitation; and it is certain that none of these agents appear capable of reaching with their influences very far down into the depths of the great and wide sea. They go not much, if any, farther down than the light can reach. On the other hand, the most powerful agents in the atmosphere reside at and near its bottom; so that, where these two great oceans meet—the aqueous and the aerial—there we probably have the greatest conflict and the most powerful display of the forces that set and keep them in motion, making them to rage and roar.

601. Their depth.—The greatest depth at which running water is to be found in the sea is probably in the narrowest part of the Gulf Stream, as, coming from its mighty fountain, it issues through the Florida Pass. The deep-sea thermometer shows that even here there is a layer of cold water in the depths beneath, so that this "river in the sea" may chafe not against the solid bottom. What revelations of the telescope, what wonders of the microscope, what fact relating to the physical economy of this terrestrial globe, is more beautiful or suggestive than some of the secrets which have been fished up from the caverns of the deep, and brought to light from the hidden paths of the sea?

602. The cushion of still water—its thickness.—In my researches I have as yet found no marks of running water impressed upon