Sea level

“ But whether or not these causes would produce any important fluctuations of the sea-level is of comparatively little importance to our present inquiry, because the wide extent of marine Tertiary deposits in the northern hemisphere and their occurrence at considerable elevations above the present sea-level, afford the most conclusive proofs that great changes of sea and land have occurred throughout the entire Tertiary period ”

“ If the level of the sea were to become coincident with the mean level of the lithosphere, there would result one tri-radiate land-mass of nearly uniform outline and one continuous sheet of water broken by few islands. The actual position of sea-level lies so near the summit of the crust-heap that the varied relief of the upperThe continents. portion leads to the formation of a complicated coast-line and a great number of detached portions of land. The hydrosphere is, in fact, continuous, and the land is all in insular masses: the largest is the Old World of Europe, Asia and Africa ”

“ To make it quite clear that the surface of the Red Sea is not a sea level, but is an inclined plane, suppose the channel of the Red Sea to have a perfectly smooth and level floor, with no water in it, and a wave ten feet high to enter the Straits of Babelmandeb, and to flow up the channel, like the present surface current, at the rate of twenty miles a day for fifty days, losing daily, by evaporation, half an inch ”

“ There is also a predilection for regarding the rigid land as moving and the mobile sea-level as fixed. In reality, the sea is an extremely adaptive body that settles into the irregular hollows of the lithosphere, and is shifted about with every warping of the latter. Whatever change affects the capacity of its depressions affects also the sea-level. ”

“ The difference in the rise of the water at different heights above the sea level, and its total cessation when the distance to be lifted is, even at sea level, more than thirty-three feet, are emphasized, instead of being slurred over. ”

“ If the sea be imagined as rising 100 ft., a new coast-line, with bays and estuaries indented in the valleys, would appear at the new sea-level. If the sea sank once more to its former level, the 100-ft. contour-line with all its irregularities would be represented by the beach mark made by the sea when 100 ft. higher. If instead of receding the sea rose continuously at the rate of 100 ft. per day, a series of levels 100 ft. above one another would be marked daily upon the land until at last the highest mountain peaks appeared as islands less than 100 ft. ”

“ The cause of this change of level in the water-surface is the attraction exerted by the sun and moon upon the ocean. The earth is, so to speak, clothed with a flexible garment of water, and this garment is pulled out of shape by the attractive force of our luminaries; very roughly speaking, we may say that the ocean-surface is distorted into a shape called an ellipsoid, and that there are therefore two elevations of water which march across the sea-covered regions of the earth as it revolves on its axis. ”

“ But also the powerful attraction of the land, particularly of great mountain ranges, lifts the sea-surface in some regions hundreds of feet higher than in others. So that a ship, passing from the neighbourhood of a mountainous coast to [p. 128] mid-ocean, may be actually sailing or steaming downhill, actually descending a vast gentle watery slope.
Another question as to Ocean’s level has much exercised the minds of men.
Throughout the world, remains of sea-creatures in countless multitudes are found embedded in the substance of water-built rocks: sometimes the very rocks being made up of them. ”

“ When, through adjustment of the relations between continental masses and masses beneath the oceans, the internal stresses of the globe have been balanced, the average elevation of lands above sea level is a maximum. ”

“ The trail passes along on high ground—say a thousand feet above sea level—and usually about a mile distant from the ocean, which is always in sight, save that occasionally you find yourself buried in the forest in the midst of a rank tropical vegetation and a dense growth of trees, whose great bows overarch the road and shut out sun and sea and everything, and leave you in a dim, shady tunnel, haunted with invisible singing birds and fragrant with the odor of flowers. ”

“ Why, it may be asked, if the ancient bed of the sea has been in many regions uplifted to the height of two or three miles, and sometimes twice that altitude, and if it can be proved that some single formations are of themselves two or three miles thick, do we so often find several important groups resting one upon the other, yet attaining only the height of a few hundred feet above the level of the sea? ”

“ Thus, it appears that the level of the sea is sinking in the more northern latitudes, and rising in the Mediterranean, and it is evident that this cannot happen by the motion of the sea itself. The parts of the ocean all communicating with one another, cannot rise in one place and fall in another; but, in order to maintain a level surface, must rise equally or fall equally over the whole of its extent. ”

“ Suppose, however, that the sea-level rose instead of falling, at the same slow and gradual rate at which we know it to be rising in some parts of the world,—not more, in fact, than a few inches, or, at most, a foot or two, in a hundred years. ”

“ When ocean electric cables for connecting islands and continents are laid, engineers find that there are the same sort of plains, mountains, valleys, and gorges beneath as above the waters of the ocean. The skeletons of whales, and natural beds of deep-sea shells, found in valleys and hills many hundred feet above the present level of tide waters, tell us plainly enough that in the long ages which have passed, the diversified surface of the earth which we now behold has changed places with these submerged regions, which probably once formed the dry land. ”

“ The highest point of the land raised above the level of the sea is much less elevated than the bottom of the sea is depressed from the same level, so that the mass of the land above this level can be estimated only at about a fortieth part of the mass of the waters. ”

“ When a land has been newly elevated above the sea there is often—we may say, indeed, generally—a very great difference between the height of its head waters and the ocean level. In this condition of a country the rivers have what we may call a new aspect; their valleys are commonly narrow and rather steep, waterfalls are apt to abound, and the alluvial terraces are relatively small in extent. ”

“ From his high perch, one sees before him and below him, a wall of dreary mountains, shorn of vegetation, glaring fiercely in the sun; it fences in a level desert of yellow sand, smooth as velvet and threaded far away with fine lines that stand for roads, and dotted with creeping mites we know are camel-trains and journeying men; right in the midst of the desert is spread a billowy expanse of green foliage; and nestling in its heart sits the great white city, like an island of pearls and opals gleaming out of a sea of emeralds. ”

“ What in water did Bloom, waterlover, drawer of water, watercarrier, returning to the range, admire?
Its universality: its democratic equality and constancy to its nature in seeking its own level: its vastness in the ocean of Mercator’s projection: its unplumbed profundity in the Sundam trench of the Pacific exceeding 8000 fathoms: the restlessness of its waves and surface particles visiting in turn all points of its seaboard: the independence of its units: the variability of states of sea: its hydrostatic quiescence in calm: its hydrokinetic turgidity in neap and spring tides: ”

“ Two thousand miles of ceaseless rush and rattle and clatter, by night and by day, and never a weary moment, never a lapse of interest! The first seven hundred miles a level continent, its grassy carpet greener and softer and smoother than any sea and figured with designs fitted to its magnitude—the shadows of the clouds. ”

“ When we travel out upon the ocean, and get beyond the influence of the land upon the winds, we find ourselves in a field particularly favorable for studying the general laws of atmospherical circulation. Here, beyond the reach of the great equatorial and polar currents of the sea, there are no unduly heated surfaces, no mountain ranges, or other obstructions to the circulation of the atmosphere — nothing to disturb it in its natural courses. The sea, therefore, is the field for observing the operations of the general laws which govern the movements of the great aerial ocean. ”

“ This rise and fall of the waters along the coast, accompanied frequently by strong currents, are produced directly by the arrival in the shoal water of a pulsation of the ocean, which becomes a true onward-moving gravity wave as it nears the land. In the open sea the amplitude of the tidal undulations is but two or three feet, and their rate of travel in general 700 to 800 miles per hour. ”

“ None of them knew the color of the sky. Their eyes glanced level, and were fastened upon the waves that swept toward them. These waves were of the hue of slate, save for the tops, which were of foaming white, and all of the men knew the colors of the sea. The horizon narrowed and widened, and dipped and rose, and at all times its edge was jagged with waves that seemed thrust up in points like rocks. ”

“ When considering the bottom of the ocean, we have, in the imagination, been disposed to regard the waters of the sea as a great cushion, placed between the air and the bottom of the ocean to protect and defend it from these abrading agencies of the atmosphere. ”

“ Tahoe! It suggests no crystal waters, no picturesque shores, no sublimity. Tahoe for a sea in the clouds: a sea that has character, and asserts it in solemn calms, at times, at times in savage storms; a sea, whose royal seclusion is guarded by a cordon of sentinel peaks that lift their frosty fronts nine thousand feet above the level world; a sea whose every aspect is impressive, whose belongings are all beautiful, whose lonely majesty types the Deity! ”

“ Continental surfaces are known to be productive of extremes of temperature, while the climate of sea areas is comparatively equable; and the general character of the climate of land and water surfaces is further and locally affected by the configuration and altitude of the land, by the breadth and depth of the oceanic basins, and especially by the ocean-currents. The sea forms the great evaporating surface, and the source from which is derived the enormous quantity of water transported by the system of atmospheric circulation. ”

“ The height to which the drift-timber is thrown up on the shores at the western entrance of the Dolphin and Union Straits is, I think, an indication of an occasional great rise in the sea, which, as the tides are in comparison so insignificant, I can ascribe only to the north-west winds driving the waters of an open sea towards the funnel-shaped entrance of the straits. ”

“ In the western half, reaching up from the equator to the Gulf Stream, both of the North Atlantic and North Pacific, the water is warmer, parallel for parallel, than it is in the eastern half. On the west side, where the water is warm, the flow is to the north; on the east side, where the temperature is lower, the flow is to the south—making good the remark (§ 80) that, when the waters of the sea meet in currents, the tendency of the warm is to seek cooler latitudes ”

“ Besides the intricate labyrinth of islands, reefs, rocks, and shoals which are scattered over its surface, there are recorded the variations of the compass, the directions of the ocean currents, and the results of countless soundings. Running your pencil through all the points on this map for which the indicated depth is fifteen hundred fathoms or thereabouts, you will be able to trace out an irregular and more or less interrupted band, extending from the East Indian seas nearly to the coast of South America. Within the area thus marked out the sea is comparatively shallow ”

“ Within a few years, the progress of scientific knowledge has enabled man to measure the depths of the ocean, which were formerly believed to be as unfathomable as boundless in extent. From soundings which have been taken, it is ascertained that the configuration of the earth at the bottom of the sea, is similar to that portion which rises above the surface, undulating, and interspersed with hills, and valleys, and plains, and mountain ranges, and abrupt precipices. ”

“ A proper conception of the bathymetry of Polar seas is necessary for an adequate discussion of physical problems connected with the temperature, salinity, specific gravity and circulation, and the effect of wind, air-temperature and other phenomena that affect these seas. The physical problems of ice-covered seas are much more complicated than in seas where there is no ice, because, as we have seen previously, when the surface of the sea is being frozen over, the salt in that part of the water which is changed into ice is thrown out and must therefore make the neighbouring water more saline ”

“ All recent observations, he said, have shown that the vast expanse of water which has its centre in the southern hemisphere is the one great ocean of the world, and the Atlantic with the Arctic Sea, and the North Pacific, are merely its northward-extending gulfs: any physical phenomena affecting obviously one portion of its area must be regarded as one-of an interdependent system of phenomena affecting the ocean as a whole. ”