>Extent of the Ocean.—Length of its Coast-Line.—Mural, Rocky, and Flat Coasts.—How deep is the Sea?—Average Depth of the Atlantic Ocean.—The Telegraphic Plateau between Newfoundland and Ireland.—Measurement of Depth by the Rapidity of the Tide-Wave.—Progressive Changes in the Limits of the Ocean.—Alluvial Deposits.—Upheaving.—Subsidence.—Does the Level of the Sea remain unchanged, and is it everywhere the same?—Composition and Temperature of Sea-Water.—Its intrinsic Colour.—The Azure Grotto at Capri.—Modification of Colour owing to Animals and Plants.—Submarine Landscapes viewed through the Clear Waters.
Of all the gods that divide the empire of the earth, Neptune rules over the widest realms. If a giant-hand were to uproot the Andes and cast them into the sea, they would be engulphed in the abyss, and scarcely raise the general level of the waters.
The South American Pampas, bounded on the north by tropical palm-trees, and on the south by wintry firs, are no doubt of magnificent dimensions, yet these vast deserts seem insignificant when compared with the boundless plains of earth-encircling ocean. Nay! a whole continent, even America or Asia, appears small against the immensity of the sea, which covers with its rolling waves nearly three-fourths of the entire surface of the globe.
A single glance over the map shows us at once how very unequally water and land are distributed. In one part we see continents and islands closely grouped together, while in another the sea widely spreads in one unbroken plain; here vast peninsulas stretch far away into the domains of ocean, while there immense gulfs plunge deeply into the bosom of the land. At first sight it might appear as if blind chance had presided over this distribution, but a nearer view convinces us that providential laws have established the existing relations between the solid and fluid surfaces of the earth. If the sea had been much smaller, or if the greatest mass of land had been concentrated in the tropical zone, all the meteorological phenomena on which the existence of actual organic life depends would have been so different, that it is doubtful whether man could then have existed, and certain that, under those altered circumstances, he never would have attained his present state of civilisation. The dependence of our intellectual development upon the existing configuration of the earth, convinces us that Divine wisdom and not chaotic anarchy has from all eternity presided over the destinies of our planet.
The length of all the coasts which form the boundary between sea and land can only be roughly estimated, for who has accurately measured the numberless windings of so many shores? The entire coast line of deeply indented Europe and her larger isles measures about 21,600 miles, equal to the circumference of the earth; while the shores of compact Africa extend to a length of only 14,000 miles. I need hardly point out how greatly Europe's irregular outlines have contributed to the early development of her superior civilisation and political predominance. The coasts of America measure about 45,000 miles, those of Asia 40,000, while those of Australia and Polynesia may safely be estimated at 16,000. Thus the entire coast-line of the globe amounts to about 136,000 miles, which it would take the best pedestrian full twenty-five years to traverse from end to end.
How different is the aspect of these shores along which the ever-restless sea continually rises or falls! Here steep rock-walls tower up from the deep, while there a low sandy beach extends its flat profile as far as the eye can reach. While some coasts are scorched by the vertical sunbeam, others are perpetually blocked up with ice. Here the safe harbour bids welcome to the weather-beaten sailor, the lighthouse greets him from afar with friendly ray; the experienced pilot hastens to guide him to the port, and all along the smiling margin of the land rise the peaceful dwellings of civilised man. There, on the contrary, the roaring breakers burst upon the shore of some dreary wilderness, the domain of the savage or the brute. What a wonderful variety of scenes unrolls itself before our fancy as it roams along the coasts of ocean from zone to zone! what changes, as it wanders from the palm-girt coral island of the tropical seas to the melancholy strands where, verging towards the poles, all vegetable life expires! and how magnificently grand does the idea of ocean swell out in our imagination, when we consider that its various shores witness at one and the same time the rising and the setting of the sun, the darkness of night and the full blaze of day, the rigour of winter and the smiling cheerfulness of spring!
Beachy Head.
The different formation of sea-coasts has necessarily a great influence on commercial intercourse. Bold mural coasts, rising precipitously from the deep sea, generally possess the best harbours. Rocky shores also afford many good ports, but most frequently only for smaller vessels, and of difficult access, on account of the many isolated cliffs and reefs which characterise this species of coast formation.
In places where high lands reach down to the coast, the immediate depth of the sea is proportionably great; but wherever the surface rises gently landwards, the sea-bed continues with a corresponding slope downwards. On these flat coasts the tides roll over a sandy or shingly beach; and here the aid of human industry is frequently required to create artificial ports, or to prevent those already existing from being choked with sand.