CHAPTER X.

CHANGES IN OCEANIC REGIONS.

W

E have now arrived at a very interesting department of Physical Geography - the consideration of the changes to which the surface of the globe is subject, and of the causes which produce them, already indicated in the preceding pages. From the experience of many an individual life, it might be imagined, that "all things continue as they were from the beginning of the creation"- that an immutable character belongs to the earth's external aspect- so uniform are the appearances presented by nature during the course of man's threescore years and ten. The grandsire, trembling with age and infirmity, and living in a country distant from the centres of volcanic action, sees no alteration in the configuration of the hills and valleys with which he has been surrounded from his childhood. The stream wanders in the same channel, with as much transparency, and with as many circling eddies, now that he is old and grey-headed, as when in youth he romped upon its banks, and plucked with careless hand the daisy or the cowslip from its grassy slopes. There is, however, no part of the globe free from physical change, whether bare to the light and air of heaven, or lying a thousand fathoms deep below the waters, though it may require the lapse of ages to discover the signs of alteration, and though circumstances may forbid the mutation being the subject of sensible evidence. The bed of the ocean must of necessity be constantly undergoing changes, extensive and diversified, wrought in secret places, into which the inquisitive eye of man cannot penetrate, and which are often beyond the reach of his longest sounding-line. "All the rivers run into the sea, yet the sea is not full: unto the place from whence the rivers come, thither they return again." Denudation, or the carrying away a portion of the solid materials of the land through which they flow, is one effect of their action. It transpires with varying energy, according to the velocity of their current, and the nature of the contiguous soil; and the distribution of the material of which the land is robbed takes place under the control of these two particulars. The heavier debris of rivers may be generally deposited in their own channels, where there is a marked diminution in the power of the stream, arising from its course lying through an extensive level; but the finer particles are transported to a more distant locality, and are either deposited at the confluence of rivers with the sea, where the tides meet them with sufficient force to produce stagnation, or they are conveyed to a more remote resting-place by the tremendous rush of the fresh water into the bed of the deep, and the action of the oceanic

currents.

According to Major Rennell, a glass of water taken from the Ganges in the floodseason will yield about one part in four of mud. The mean quantity of water discharged by the river throughout the year he estimated to amount to 80,000 cubic feet in a second, but to be 405,000 cubic feet when the river is in flood. Calculating upon these data, Mr. Lyell states, that if the mud be assumed to be equal to one half the specific gravity of granite, a supposition below the truth, the weight of matter daily

carried down in the flood season would be about equal to seventy-four times the weight of the Great Pyramid of Egypt. He observes:- "405,000 cubic feet of water per second gives in round numbers 100,000 cubic feet of mud per second, which × 86,400, the numbers of seconds in twenty-four hours, =8,641,100,000, the quantity of cubic feet of mud going down the Ganges per diem. Assuming the specific gravity of mud to be half that of granite, the matter would equal 4,320,550,000 feet of granite. Now about twelve and a half cubic feet of granite weigh one ton; and it is computed that the Great Pyramid of Egypt, if it were a solid mass of granite, would weigh about 6,000,000 of tons." There is some reason to doubt the accuracy of Rennell respecting the quantity of earthy matter in the water of the Ganges, though it is generally agreed to be the most turbid river upon the face of the globe, owing to the lightness of the soil of the Bengal plains favouring its transportation by the current, and the great violence of the tropical rains. Supposing it therefore to hold but th part of mud in suspension, instead of, an estimate given with reference to the Rhine when most flooded, -the result will still be, that the river discharges in two days a mass of matter equal in bulk and weight to the Great Pyramid. A considerable portion of this goes to form new land along the coast at the mouth of the Ganges, but a large quantity is swept onwards into the Bay, of Bengal, and contributes to lay upon its floor a carpet of soil in course of perpetual renewal.

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The Sea of Azov, well-known to the Greeks and Romans under the name of Mæotis, was believed in the time of Aristotle to be filling up by the earthy matter conducted into it by its rivers. Its excessive shallowness now has no doubt been produced by the alluvium principally discharged by the Don, the average depth of the main body of the sea being only between six and seven fathoms. The Yellow Sea, an arm of the Chinese Ocean, so called from its waters being coloured by an intermixture of particles of yellow mud, supplies a similar example of the accumulation of debris in its bed. It receives the rapid Hoang Ho, one of the largest rivers of China, which carries along with it an immense quantity of earthy material in a state of solution in its waters. Sir George Staunton calculated that this powerful stream brought down in a single hour two million feet of earth, or forty millions daily; so if the Yellow Sea be taken to be 120 feet deep, the river will convert an English square mile into firm land in seventy days. Currents carry far away into the ocean much of the sediment it receives, but the immediate deposition of the major part produces gradually increasing shoals and shallows, which interfere with the navigation. Captain Hall in the Lyra, sailed across this sea in 1816 on his voyage to Loo Choo, and had occasion to apprehend fairly sticking in the mud several times in the passage. When no land could be perceived from the mast-head, the ship was in less than five fathoms of water, and upon the ebb of the tide, its bottom was within three feet of the ground. It was discovered, at one time, that the Lyra was actually sailing along with her keel in the mud, indicated sufficiently by a long yellow train in her wake. There was more apparent than real danger in this extreme shallowness, as it was found, by forcing long poles into the ground, that for many fathoms below the surface on which the sounding lead rested, and from which level the depth of water is estimated, the bottom consisted of nothing but mud formed of an impalpable powder, without the least particle of sand or gravel. The fact unquestionably is, that the bottom of the Yellow Sea is gradually rising, from the deposits of innumerable streams flowing into it from China and Tartary, and in process of time, this arm of the ocean, which has probably an extent of 125,000 square miles, will become terra firma, exhibiting a horizontal plain like the great deltas of the Nile and the Ganges.

While, by the action of rivers, soil is transported from far inland situations, and brought into the sea, it is borne by the currents of the ocean, which sweep along the coasts, to a

much greater distance from its original site. At not less than three hundred miles from the mouth of the Amazon, Captain Sabine found the sea discoloured by the waters of the river, where they were still running with considerable rapidity; but the stream does not deposit its load of earthy material off its own estuary, for the great tropical oceanic current westward crosses its course, takes up a part of its burden, bears it towards the Caribbean Sea, and may even strew it over the bed of the Gulf of Mexico. In like manner, the sedimentary matter which the mighty Mississippi discharges, and the rivers of the United States east of the Alleghanies, is taken up by the majestic currents of the gulf stream, and distributed over the floor of the North Atlantic. The whole extent of our own eastern coast is annually deprived of a large mass of material by the tidal current of the German Ocean. It undermines and sweeps away the granite, gneiss, trap rocks, and sandstone of Shetland, and removes the gravel and loam of the cliffs of Holderness, Norfolk, and Suffolk, which are between fifty and two hundred feet in height, and which waste at the rate of from one to six yards annually. It bears away the strata of London clay on the coast of Essex and Sheppy-consumes the chalk with its flints for many miles continuously on the shores of Kent and Sussex-commits annual ravages on the fresh-water beds, capped by a thick covering of chalk flints in Hampshire, and continually saps the foundations of the Portland limestone. It receives, besides, during the rainy months, large supplies of pebbles, sand, and mud, which numerous streams from the Grampians, Cheviots, and other chains send down to the sea. To what regions is all this matter consigned? This question is no doubt answered in part by those immense banks which are found along the coasts of England, Holland, and Denmark, and penetrate to the central regions of the German Ocean, equal to about of its whole area, or of the whole extent of Great Britain. There are thus formations proceeding upon a gigantic scale, elevating and variously shaping the bed of the ocean, the result of the deposition there of the solid materials abraded from the land by the agency of rivers and sea-currents.

It is easy to perceive, that should any upheaving cause expose to the gaze of man the bottom of the existing seas, precisely similar phenomena would be exhibited to those which the continents now present. Vast spaces of regular strata would appear, bearing clear marks of having been formed by aqueous deposition, slowly and horizontally, however inclined and fractured by the power of the elevating agent.

In addition to the soil transported from inland regions into the heart of the ocean, the plants and trees which fall into the river-channels through the undermining of their banks, or which are uprooted by their agency in floods, undergo a similar transference, and are finally imbedded in the sediment accumulating below the waters of the deep. When we reflect upon the combined influence and constant action of innumerable streams in this respect, we shall readily admit that, in the course of a few ages, a prodigious quantity of animal and vegetable remains, derived from the existing continents, receives. a subaqueous deposition, similar remains of marine species contribute largely to augment and diversify the formations in process at the bottom of the seas. We have referred to huge fragments of rock borne by icebergs from the shores into the central parts of the ocean, and there submerged upon the dissolution of their frozen vehicles; and this single operation must, in a century or two, work great changes, scattering isolated blocks upon the sandy slopes and plains over which the North Atlantic rolls its waves, or piling them upon each other in every variety of form. Shakespeare, in describing the dream of Clarence, draws a vivid picture of other contributions which the occurrence of disaster annually submerges, involving many of the human race, with the monuments of their industry, and the signs of their opulence.

Methought that I had broken from the Tower,
And was embarked to cross to Burgundy;

And, in my company, my brother Gloster:
Who from my cabin tempted me to walk

Upon the hatches; thence we look'd toward England,
And cited up a thousand heavy times,

During the wars of York and Lancaster,

That had befallen us. As we paced along

Upon the giddy footing of the hatches,

Methought that Gloster stumbled and in falling,
Struck me, that thought to stay him, overboard,
Into the trembling billows of the main.

O Lord! methought what pain it was to drown!
What dreadful noise of water in mine ears!
What sights of ugly death within mine eyes!
Methought I saw a thousand fearful wrecks;
A thousand men, that fishes gnawed upon,
Wedges of gold, great anchors, heaps of pearl,
Inestimable stores, unvalued jewels,

All scattered in the bottom of the sea.

Some lay in dead men's skulls; and in those holes

Where eyes did once inhabit, there were crept,

(As if in scorn of eyes) reflecting gems,

That woo'd the slimy bottom of the deep,

And mock'd the dead bones that lay scattered by."

During the recent wars of this country, the navies of the continental powers, Spain, France, and Denmark, were almost annihilated, and our own losses amounted to an enormous aggregate, a large number of stately vessels being battered to pieces, and consigned to the bottom of the deep. "In every one of these ships were batteries of cannon, constructed of iron or brass, whereof a great number had the dates and places of their manufacture inscribed upon them in letters cast in metal. In each there were coins of copper, silver, and often many of gold, capable of serving as valuable historical monuments; in each were an infinite variety of instruments of the arts of war and peace, many formed of materials, such as glass and earthenware, capable of lasting for indefinite ages, when once removed from the mechanical action of the waves, and buried under a mass of matter which may exclude the corroding action of sea-water.

But the reader

must not imagine that the fury of war is more conducive than the peaceful spirit of commercial enterprise to the accumulation of wrecked vessels in the bed of the sea. From an examination of Lloyd's lists, from the year 1793 to the commencement of 1829, it has appeared that the number of British vessels alone lost during that period amounted on an average to no less than one and a half daily,- -a greater number than we should have anticipated, although we learn from Moreau's tables that the number of merchant vessels employed at one time in the navigation of England and Scotland, amounts to about twenty thousand, having one with another a mean burden of one hundred and twenty tons. Out of five hundred and fifty-one ships of the royal navy lost to the country during the period above mentioned, only one hundred and sixty were taken or destroyed by the enemy, the rest having either stranded or foundered, or having been burnt by accident, a striking proof that the dangers of our naval warfare, however great, may be far exceeded by the storm, the hurricane, the shoal, and all the other perils of the deep. Millions of dollars and other coins have been sometimes submerged in a single ship, and on these, when they happen to be enveloped in a matrix capable of protecting them from chemical changes, much information of historical interest will remain inscribed, and endure for periods as indefinite, as have the delicate markings of zoophytes or lapidified plants in some of the ancient secondary rocks. In almost every large ship, moreover, there are some precious stones set in seals, and other articles of use or ornament composed of the hardest substances in nature, on which letters and various images are carved-engravings which they may retain when included in subaqueous strata, as long as a crystal preserves its natural form." This interesting statement of Mr. Lyell shows, that, independent of the remains of plants and animals washed down by rivers from the land into the ocean, a vast variety of substances, diverse in kind and form, must necessarily be included in the strata now building up below its waters; and reflecting upon the action of that power, which, at different epochs, has upheaved our mountain ranges, we may conceive of the singular spectacle that would be presented to the inquirer long ages hence, and of its close resemblance to that exhibited by the stratified rocks upon which we gaze, should an elevating cause raise up the "ooze and bottom of the deep," submerging the existing continents in compensation.

In referring to the elevation of the oceanic bed, we are not indulging in any extravagant speculation, for, besides a gradual change as the effect of deposition, a series of wellattested facts proclaim the occurrence of violent catastrophes. The sudden formation of new islands, the result of submarine volcanic action, constitute a distinct class of those mutations to which the oceanic realm is subject. Some of these islands, after a hasty start into existence have subsided, and either entirely disappeared, or become shoals slightly depressed below the level of the water, while others have remained permanent. Some also have consisted merely of volcanic matter, while others have presented marine strata, and been literally the upheaved floor of the sea.

The gulf of Santorin, one of the Cyclades, in the Grecian Archipelago, nearly encloses several small islands which have emerged from the deep within the period of authentic history. Rather more than a century before the Christian era, the small isle of Palaia Kameni was thrown up in the gulf. In the year 1573 another appeared, called the Little Kameni, a large disengagement of vapour and the discharge of pumice accompanying its elevation, and telling the story of its birth. A third was formed in the years 1707 and 1709, called the New Kameni, which still exhales sulphureous vapours. These islands consist of volcanic products, lava, scoriæ, and pumice, and of strata uplifted by the expansive force which produced the ejection of these materials.

Similar instances have repeatedly happened in connection with the Azores. The first on record is that mentioned by Kircher in 1538; another took place in 1720; and a