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We may regard the sea, if we like, as a great burialground. Subterranean forces, constantly at work, cause gradual, incessant change of level on the surface of our world. We are ourselves born just in time to see the departing peaks of a huge continent now drowned in the Pacific Ocean; where its highest mountain tops, not yet submerged, rise as innumerable islands, around which the coral polyps build. But subterranean forces have a stout ally provided in the busy sea itself. How ocean currents eat away the land, we have already seen; but we have only to look at the coast behind us, and we are reminded that the mere action of the tide is constantly engaged in chewing away shore, and taking it off, masticated into pulp, to feed the sea's great belly. Rivers, too, wear away the soil through which they rub, and carry seaward a large quantity of land, in the form of that dear pulp for which the great deep hungers. Out of the world of water vapor rises and forms clouds; they float above our fields, and fall as rain, to bless the husbandman, and give food to the mouths of men. But they feed also the great sea; they wash the soil down the mountain sides; and if they do not rise again as vapor, to form new clouds, they form streams and springs, that fertilize the ground, and, at the same time, rub down more soil for the hungry sea. Granite yields. Rain, or the vapor of water, in its pores, expanding and again contracting with the change in temperature, very slightly wears its outer crust; it is just so much loosened that a lichen
*The late Mr. Stephenson, the architect of Skerryvore, stated, at the last meeting of the British Association, that the force of waves is a ton and a half per square foot for the German Ocean, and twice as great for the Atlantic. This estimate was made with reference to the construction of marine works, from results obtained at the Bell Rock and Skerryvore.
fastens. Then the lichen holds more damp upon the stone; the water and the work of vegetation loosen it a little more; so that there presently is soil enough for mosses. Moss invites more water, the stone decays more, and is mingled with decaying vegetable matter; the conversion into loose soil has begun; man will reap profit from it; but, in due time, it will come into the sea. The waste of continents strewed thus over the bottom of the ocean goes to Build up, layer upon layer, land that shall hereafter be. So layers under layers tell us of the ages that have past, and yield to our sight skeletons of creatures that have lived a thousand, thousand years ago. Man came, as you know, late into the world; we never dig him up as a contemporary of the creatures that are gone: his bones and his works are being now deposited in the great burial-ground. What fleets have gone down into the deep we know; how many monuments of man are being buried in the mud of our own age, to be dug up, as antiquities, perhaps, when man shall be extinct. It is not easy to imagine one's self a fossil; but the Megalotherium, no doubt, never expected it. An English river being crossed, some centuries ago, by one of our armies, the great military chest, with all its treasure, was upset and drowned; nor was there time to fish it up again. Ten years ago a piece of rock, which seemed to be hard sandstone, found upon that spot, astonished all beholders. In its substance was a store of fossil coins; and, on examination, it turned out that all the sand into which coins had sunk, after the chest rotted, had been quite converted into rock by the chemical action of iron from the hoops with which the chest had been originally bound. Coins thus imbedded have been got up also from the Thames, in London. Of man there is no such record in the geological past; but in the geological future, should the race of anti
quaries still hold out, there will be joy in digging for him, and for all the produce of his hands, now being locked up carefully beneath the waters of the world.
Some of the lime washed down into the sea is used by countless animals, who make to themselves shells. But it is almost certain that the shells of molluscs and other marine animals do not grow wholly from this scource. It is more likely that the basis of lime, calcium, is not an element, although we call it so, until we know how to resolve it into simpler forms. Probably it is not an element, and is produced by the animals from its constituents existing in sea water. If so, a large part of the shore of Albion has actually once been sea; for our chalk cliffs are nothing less wonderful than an aggregate of myriads on myriads of microscopic beings, whose remains have strewed the bottom of the ocean, and been subsequently lifted up in chalk beds of amazing thickness.
The ocean is not only a destroyer; it contributes of its soil to pile up reefs, until they reach the highest watermark. It catches nuts and seeds into its currents, and industriously scatters them on foreign shores; it scatters them upon the bald little island, and there soon grows thereupon a busy crop. Busy old ocean seizes a canoe, and carries it upon a current far out of sight of land. "Come with me, good little men and women," roars the old fellow, and he shoots them presently upon the island he has made; and there they live, perforce, and their descendants people it. The sea bore no inactive part, assisted by the tradewind, in getting over the first ships from Europe to Amer ica.
These ocean currents play, unobtrusively, a large part in the history of man. But, as Britons, we must leave ourselves a little time to talk about the waves, because they are precisely what "Britannia rules." You know all about the
tides, only as M. Jourdain says of his Latin, we had better "make as if you didn't." The rise of tide is caused, of course, by the attractive forces of the sun and moon, mainly exerted, as we said, on the south polar reservoir. There should be two tides to each luminary, one on its upper and one on its lower transit; four tides a day; but the attraction of the lady moon being, as it ought to be, six times greater than that of the sun, who is a distant gentleman, she reduces the sun's tide to a mere supplement. When the gentleman and lady pull together, then the sun's pull adds one foot of height to every five feet produced by the moon, and makes a spring-tide. When the sun and moon pull in opposite directions, and the sun wants a high tide where the moon wants low water, from every six feet of the moon's tide the sun is able to take one away, and neap-tides
are the consequence. The varying elevations of the tide at the same place depending on the varying degree of unanimity between master and mistress in the sky.
In different places, however, the height of the same tide varies considerably-from three inches to thirty feet. This depends on the conformation of the land. The great tide wave, commencing in the Antarctic Ocean, has its whole course directed by the coast lines. It flows into the Indian Ocean, where it finds no northern outlet, and breaks violently on the shores of Hindostan; rushing into the ready mouths of the Ganges, it produces the great bore of the Hoogly. It should flow into the Pacific, but it finds that ocean barricaded by innumerable shoals, islands, and coral reefs; there is no deep, uninterrupted mass of water, and the tidal movement runs weakly up the western coast of America, penetrates not far between New Zealand and Australia, leaving the shores of China and Japan, with the great
mass of the Pacific islands, almost wholly unaffected by the tidal wave. Into the Atlantic it breaks round the southern point of Africa; the wave that struck the south shore of New Zealand washes the Cape fifteen hours afterwards, and passes on up the Atlantic, touching Africa on one side, America upon the other. Deflected variously by the line of coast, after another fifteen hours of travel, it is ready to come down upon Cape Clear. Cape Clear and Land's End are struck by the wave in the next hour, which then communicates its impulse through the Irish and St. George's Channels. The rate of movement of the tide wave depends upon the nature and depth of the sea bottom. With a depth of one fathom, its rate is eight miles an hour, and with one hundred fathoms eighty miles an hour; while through deep water of a thousand fathoms, it is propagated at the speed of about four miles a minute. Thus the same wave which touched Cape Clear, passes, in little more than an hour, on the Atlantic side to touch the Hebrides, yet takes four hours in working up the Irish Channel, only to Dublin. So, also, it is a seven hours' journey for the tide along St. George's Channel from Land's End to London, which is about the time it occupied in travelling from Rio Janeiro to New York. The tide at London is, however, ruled by the stronger wave that has rolled round the Orkneys, and descended thence in about fifteen hours through the German Ocean to reach London Bridge, on the third day after its start from the great southern sea. A glance at the map will show how small a part of the great tidal impulse can be communicated to the Mediterranean through the Straits of Gibraltar; accordingly, we find a tide of only thirteen inches on the northern coast of Africa, near to the Straits, and two, three, four, or five inches in more