Seafloor

“ The floor of the sea is consequently always receiving additions in the form of fine mud—the waste of the land—derived either from breaker-action, rivers, or icebergs, so that a series of marine deposits exactly similar to those we find among the rocks of our hills and valleys, must - 174 - be constantly in the course of formation. If circumstances be favourable, the shingle of the beach may eventually either be covered over or reach a part of the sea undisturbed by currents or waves, and then consolidate into what we call conglomerate or pudding-stone. ”

“ Thus our simple hypothesis acquires the majesty of truth, for we are now prepared boldly to assert we know that the sea has its system of circulation, because it transports materials for the coral insect and its rock from one part of the world to another; because its currents receive them from the rivers, and hand them over to the little mason for the structure of the most stupendous works of solid masonry that man has ever seen—the coral islands of the sea. ”

“ The area protected by the sea wall, as low as the sea level, was covered all over with long, rank grass. At the north end of the islet a curious round rock, exactly like a martello tower, but rather higher, rose out of the water, separated from the sea wall by twenty or thirty feet of deep water, dark blue, transparent; sometimes rolling and rushing and tearing at the sides of the rock, sometimes gently lifting the sea-weed that clung to the sides. Round the top of the rock flew, screaming, all the year round, the sea birds. ”

“ When a heavy sea comes on, it breaks over the ridges of rubble-rocks, which are interspersed amongst the timber of the staging, and gradually lowers them, carrying away ridge after ridge, until that which was far above the water is completely submerged; and the sea acting upon these stones gradually solidifies the mass, which binds itself into the clayey bottom of the harbour, and the whole becomes tenaciously cemented to the ground. And this process will go on until the deposit shall have formed a place sufficiently inclined to sustain the breaking of the sea without removal. ”

“ THE FLOOR OF THE OCEAN. The wonders of the ocean floor do not reveal themselves to vulgar eyes. As the oracle was inaudible to sacrilegious listeners, and as none but poetic ears heard the cadenced beating of the feet that danced to unearthly music, near the fountain haunted by the Muses of classic fable—so, none but the initiated can see the myriad miracles that each receding tide reveals on the ocean floor. ”

“ What we may term the littoral or shore zone of the sea occupies a belt of prevailingly shallow water, varying in width from a few score to a few hundred miles. Where the bottom descends steeply from the coast, where there are no strong off-shore setting currents, and where the region is not near the mouth of a large river which bears a great tide of sediment to the sea, the land waste may not affect the bottom for more than a mile or two from the shore. ”

“ Later youth is characterized by a large accumulation of shore waste. The rock bench has been cut back so that it now furnishes a good roadway for shore drift. The stream of alongshore drift grows larger and larger, filling the heads of the smaller bays with beaches, building spits and hooks, and tying islands with sand bars to the mainland. It bridges the larger bays with bay bars, while their length is being reduced as their inclosing promontories are cut back by the waves. ”

“ The ocean, in its action upon the cliffs and banks situated on the coast, breaks them down to a greater or less extent, and either accumulates the debris at their basis in the form of sea beaches of greater or less magnitude, or by currents carries it away to be deposited upon other shores, or to give rise to sand-banks near the coast, which, in the course of time, become united to the land, and thus secure it from the further action of the sea. ”

“ About their margins, the deposits of lake and ocean are thus in large part wrested by the waves from the neighboring land. Their distribution is always such that the coarsest materials are laid down nearest to the shore, and the deposits become ever finer in the direction of deeper water. Relatively far from shore may be found the finest sands and muds or calcareous deposits, while near the shore are sands, and, finally, along the beach, beds of beach pebbles or shingle. When cemented into coherent rocks, these deposits become shales or limestones, sandstones, and conglomerates, respectively. ”

“ Walking along the sea shore, with all its varied interest, many must from time to time have had their attention attracted by the shells to be seen, not lying on the sands, or in the pools, but firmly embedded in the solid rock of the cliffs and of the rock ledges which run out on to the shore, and have, it may be, wondered sometimes how they got there. ”

“ The formation of the slabs, and the preservation of the footprints, are processes which the geologist can easily explain. A beach on which animals have left the marks of their feet, becomes sufficiently hardened to retain the impressions; another layer of sand or mud is laid down by perhaps the next tide, covering up the first, and protecting it from all subsequent injury. ”

“ Nor is this surprising, when we remember that all creatures naturally desire something which they have not got. For the bottom of the sea itself is no beach at all, but chalk or sand, and sometimes hardened sandstone, with, I dare say, many precipitous pits and hollows, and many pointed crags. Here, gigantic fronds of the oar-weed wave to and fro among thousands of acres of dulse and bladderwrack ”

“ Precipices cut down to the sea-beach, constantly hammered by the waves, and constantly crumbling; the beach itself made of the flints outstanding after the softer chalk has been ground down and washed away; themselves grinding one another under the same ceaseless discipline—first rounded into pebbles, then worn into sand, and then carried further and further down the slope, to be replaced by fresh ones from the same source. ”

“ A single row of piles driven into the beach at right angles to the shore, wherever a shallow exists, will be sufficient, with plank fastened to them, to encourage the materials, brought by the tidal wave and current, to be retained and lodged against them. The length of the piles necessary, must depend upon the supposed elevation required, taking into consideration, not only the depth of the sand lying at the bottom of the shallow, but also the strata beneath. ”

“ Solid as the ground appears, all is subject to elemental change and motion; and whenever the waves of the sea or the strong current of a river can plough some crumbling chine, or wear away the face of a cliff, down come the imbedded pebbles and crystals, and gradually form a beach upon the margin of the ocean. ”

“ He had walked down to the sands with his aunt and there were assembled various younger members of the Balfour clique, and some whom age and sex ought perhaps to have taught to despise, though it had not, the hoydenish pleasures of 'a sea-house.' A 'sea-house,' for the benefit of the uninitiated, is a deep hole dug in the sand while the tide is out, and the sand taken from the hole is built round in broad, high walls to make the fort resist as long as possible the rush of the incoming waves. ”

“ The evidences of this depression are found in the numerous beds of stratified sand and gravel—elevated beaches and other shore-formations—which lie along the central ridge of hills, [6] and fronting the ocean from 100 to 260 or more feet above the level of the sea. At whatever heights these deposits occur, they suggest, if they do not prove, submergence of the coast to that extent. ”

“ With the growth of commerce32 one section after another could be added to meet the needs. The front sea wall should be built of stone or concrete, while the transverse wall between the sea wall and the land side should be built of sand and bush mattress as a temporary structure to be removed in case of the extension of the harbor. Once a harbor is formed there need be no trouble regarding the future conservancy work, for there is no silt-carrying water in the vicinity by which the harbor and its approaches may be silted up afterwards. ”

“ Compared with the former, these recent formations are of very limited extent; they consist of the sand and stones that are accumulated on the sea coast by tides and currents; of the land washed away from one bank of a river, and thrown up on the opposite bank by the winding stream; of the earth and gravel, and fragments of rock, carried down by all rivers, and forming deposits at their mouths; and of the constant increase of marsh land, in consequence of the growth of aquatic plants. ”

“ While the lowest rock in the series of strata was a hard grey sandstone, full of fossil shells, and forming a kind of level terrace skirting the beach, and a wash at high tide, on the north side of the bay this last-mentioned rock was continuous with another horizontal terrace, which ran at a somewhat higher level, as if introduced there by a fault in the strata. ”

“ But the deposition of earthy matter does not suddenly come to an end when we reach the present line of the coast. The sea is visibly discolored by the sediment far beyond the actual base of the Delta; and a sloping bank of mud is found to stretch beneath the waters of the Bay to a distance of a hundred miles.
Even within the short period of a man’s life the domain of dry land is often visibly enlarged. ”

“ The coast is so narrow at this spot that there are but a few paces' breadth between the façade of the building and the sea, so that, in order to have a fair view of the whole, one must take a boat and put out from the shore until the proper point of view is found. Now it is not every one who will be disposed to take this trouble solely for the purpose of appreciating the effect of a façade. ”

“ The clay used in the building of the boat would, I thought, be sufficient in quantity to give the floor and the walls inside and out a good coat, and this when once dry would make the structure like an adobe building. I intended, moreover, to add an extra thickness of thatch, put in a row of glass photograph plates toward the sea for windows, make a good cedar door, to be hung on wooden hinges, and add a wide veranda to the front, under which I might sit in the evening. ”

“ The shifting action of tidal currents succeeds in giving rise to very irregular deposits in shallow seas. The soundings often shew sudden changes from gravel to sand and mud, nor can there be any doubt that, could we lay bare the sea-bottom, we should often observe gravel shading off into sand, and sand into mud, and vice versâ. ”

“ The rocks, laid bare by the tide, belong to the bed of coarse-grained red sandstone, varying from eighty to a hundred and fifty feet in thickness, which lies between the lower fish-bed and the great conglomerate, and which, in not a few of its strata, passes itself into a species of conglomerate, different only from that which it overlies, in [Pg 271] being more finely comminuted. The continuity of this bed, like that of the deposit on which it rests, is very remarkable. ”

“ The persistence of the range, the regularity of the system, the many signs along the seaboard of an ever-increasing development in the scale of the mountain walls which lie behind—all contribute to the growing consciousness that this foot of the barrier, the pleasing inlets of this shore, are but the threshold of some commanding piece of natural architecture of which we long to realise the plan. ”

“ Not only barriers and reefs owe their origin to these humble means, but large lands, stretching for miles in the centre of the ocean, rise gradually from beneath the surface of the sea, and, becoming clothed with verdure and vegetation, at last offer a resting-place for the daring seafarer. ”

“ When the direction of the waves is oblique to the coast, the sands are borne to a distance, but when it is perpendicular to the coast, the waves raise the sands brought by the ground swell into dykes and banks, which protect the low shores. The most minute and lightest portions are accumulated at the more elevated points of the flats, where, being dried by the sun, they are soon carried away by the wind, which leaves them, in its turn, in the shape of downs. ”

“ Although sand and gravel are distributed over the bottom of the ocean near the land, dredging expeditions reaching down their metal cylinders for samples of the sea-floor at greater depths in various sections of the globe, have discovered that it is of a different composition, one-third of its area being covered with red clay. ”

“ A plausible hypothesis is, that while the ocean was breaking on the mainland shore and forming the Quaternary terraces, which may be seen there, sand-bars were made under water, and that the continental elevation which raised these terraces to their present position from twenty-five to eighty feet above tide, brought these sand-bars above water into a horizon of Æolian action. Once above the sea, the beaches would maintain their existence. ”

“ We find that whenever the shore is flat the shingle and sand are blown inwards and form “dunes,” and the sand is distributed far inland, checking all vegetation, and altering the features of the country. The wearing away of rocks by the water, the continual undermining of them by the waves, and sometimes the disengagement of great blocks weighing many tons—all these effects of the sea tend to alter the appearance of the land. ”