have, during the lapse of ages been filled up by its annual deposites.

In the course of this river, it receives the waters of a vast number of springs containing carbonate of lime in solution, and which mixing with the waters of the Rhone, is not deposited until it reaches the sea. Hence the Delta of this river, instead of consisting of loose, incoherent sediment, like the deposites from most other rivers, consists chiefly of solid rock; the carbonate of lime acting as a cement to the sediment, when this exists, or in its absence, forming limestone nearly pure. This is a well ascertained fact, for large masses of this rock are quarried for various purposes, and are found to consist of sand consolidated by a calcareous cement, and mixed with broken shells. After the sand has been deposited, the waters still hold a portion of the carbonate in solution, which is thrown down in a purer state, and even sometimes in the form of crystalline masses. As an example, there exists a cannon in the museum of Montpelier, taken up from near the mouth of this river embedded in crystalline limestone.

Thus we see that solid limestone is now constantly forming, in which are embedded shells as in the ancient marbles, which some geologists have contended were thousands of years older than the creation according to Moses. This circumstance is important and will be adverted to in another place.

In a late survey of the coast of the Mediterranean, the ships employed at the mouth of the Rhone were obliged to quit their moorings, when the wind blew strongly from the south-west. Captain Smith, one of the officers on this service, states, that when the ships returned after such a wind, the new sand banks in the Delta were found covered with a great abundance of marine shells, which were swept there by the current caused by the wind. This circumstance appears to explain phenomena of some importance in geology. In some ancient strata it has been claimed that marine and fresh water shells alternate with each other, and hence it has been supposed that at least in such places, the sea had retired for a time, while fresh water occupied its place; after which the sea again resumed its former bed; and so alternately, as often as the different kinds of shells were repeated. But it appears from the above statement, that the explanation of such appearances is very simple, and that it is unnecessary

to believe that the ordinary course of nature was changed in order to produce such effects: for, at the mouth of the Rhone, a strong south-west wind only is required, to occasionally mix the shells of the sea with those which are brought down by the fresh water, or which live in its current.

Delta of the Po in the Adriatic. We have already described the effects which the Po has produced and is now producing, in some parts of the country through which it passes. But we must notice more particularly the changes which this mighty torrent, assisted by the Adige, has produced at its delta in the Adriatic.

These two rivers with numerous smaller streams, drain some of the loftiest ridges of the Appenines, together with one side of the great Crescent of the Alps. The combined influence of these rivers have produced an enormous increase of alluvial matter along the coast of that sea. From the northernmost point of the gulf of Trieste where the river Isonzo enters, down to the south of Ravenna, there is an uninterrupted series of recent alluvial deposites, forming dry land, more than one hundred miles in length, and from two to twenty miles in breadth. There is evidence that this great alluvion has been formed within the last two thousand years. Adria a city which gave name to the Adriatic, was originally a sea-port; it is now twenty miles from the sea. Ravenna and Spina were also built on the sea, but, at the present time, the first is four, and the last ten or twelve miles from the water.

Delta of the Ganges. The Ganges and the Burrampooter descend from Himmala mountains, the most lofty on the globe. The latter river may be considered as a branch of the former, and falls into it long before their united waters reach the sea. The Ganges is discharged into the Bay of Bengal, which forms a vast indenture into the continent of more than two hundred miles in length. The Delta of the Ganges commences more than 200 miles from the Bay of Bengal in a direct line, and 300, if the distance be estimated along the windings of the river. That part of the Delta which borders on the sea, is divided by a vast number of rivers, or creeks, all of which are salt except those which communicate with the prin

cipal arms of the Ganges. This tract is famous under the name of Sunderbunds being the common haunt of tigers and alligators. Its extent, according to the account of Major Rennell, is equal to the whole principality of Wales. Its base, bordering on the sea, is about two hundred miles in length, and, on each side, it is enclosed by an arm of the Ganges. Besides these, through which the water of this immense river is now discharged, there are six other great openings through the Delta into the sea, each of which has evidently at some ancient period, been the principal bed of the river. During the period of overflow the greater part of this vast Delta is covered with the water of the river, so that the Ganges appears to be flowing into a vast lake, instead of itself inundating, and sweeping a whole territory of India. So great is the quantity of mud and sand carried down by this immense current, at such seasons, and so vast the quantity of water it discharges, that the ocean is discolored by it to the distance of sixty miles from its mouth.

In various parts of this delta great accumulations, or islands are formed in the course of a few years, and perhaps as soon swept away, and similar ones formed in other places. Some of these, which are islands during freshets, Major Rennell states, are equal in extent to the Isle of Wight, and thickly inhabited. The people are however, always in danger of being swept away by floods of uncommon height. In 1763 such an inundation happened, the water rising six feet above ordinary floods; and consequently the inhabitants of one of these districts of considerable extent, were, with their horses and cattle totally engulfed, and perished in the water.

These examples of the effects of running water in changing the surface of the globe are sufficient for the purposes intended. In all parts of the world, such effects are constantly taking place, to a greater or less extent.

The aggregate accumulation of solid ground by the formation and extension of deltas on the surface of the whole earth, must be very considerable during every year; and yet these effects are hardly appreciable in relation to the changes they produce on the entire surface of the globe. It is true, that the course of navigation is in a few instances obstructed, or changed by these accumulations, but in general the same sea ports of which the earliest records of history give any account, are still accessible.

SEDIMENT IN RIVER WATER.

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Had their accumulations commenced at very remote periods as some have contended, and continued to the present time, it is quite certain that many lakes now existing would have become dry land, and that the deltas of rivers falling into the sea, would have been far more extensive than we find they are. All the facts therefore, which are connected with the effects of rivers in the formation of dry land, tend to show that the present form of the earth has not existed more than a few thousand years, and that it has suffered no considerable changes from running streams, as one of the causes now in operation.

QUANTITY OF SEDIMENT IN RIVER WATER.

Having in the preceding pages given such an account of the effects of rivers in forming solid depositions, as our limits will allow, it is proper here to present the geological student with an account of the estimates and experiments, which have been made to ascertain the quantity of solid matter, water is capable of holding in suspension.

It is proper, however, that we should also state that few, if any of these estimates can be considered as more than approximations to the truth; still they are such as are quoted by the best writers, and are probably as accurate as any in existence at the present day. Major Rennell states that a glass of water taken out of the Ganges during the height of its annual flood, yields about one part in four of mud. "No wonder then," says he, "that the subsiding waters should quickly form a stratum of earth, or that its delta should encroach upon the sea. The same

writer, who resided many years in the vicinity of the Ganges, computed with great care the quantity of water which that river discharges into the sea, and which by his estimate amounted, during a year, on an average, to eighty thousand cubic feet, for every second of time. When the

river is at its greatest height during its annual inundation, and consequently its motion much accelerated, the quantity discharged, by the same estimate, was four hundred and five thousand cubic feet per second.

Mr. Lyell has made a computation of the quantity of solid matter carried down by the Ganges, taking as his

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data, the experiment of Major Rennell, and his estimate of the quantity of water it discharges. "If it were true," says he, "that the Ganges in the flood season contained one part in four of mud, we should then be obliged to suppose that there passes down every four days, a quantity of mud equal in volume to the water which is discharged in the course of a day, or twenty-four hours. If the mud be assumed to be equal to one half the specific gravity of granite, (it however is more,) the weight of matter daily carried down in the flood season would be about sixty times the weight of the great pyramid of Egypt. If the Ganges discharges 405,000 cubic feet of water per second, which was the estimate of Major Rennell, then, in round numbers the quantity of mud discharged per second, would be 100,000 cubic feet, which being multiplied by 86,400, the number of seconds in 24 hours, would give 8,640,000,000 cubic feet of mud going down the Ganges per day. The weight of this, (allowing as above,) would be equal to that of 4,320,000,000 cubic feet of granite. Now about twelve and a half cubic feet of granite weigh a ton, but throwing out the half, the matter discharged by the Ganges every day 360,000,000 of tons. This is sixty times the weight of the great pyramid of Egypt, which if solid is computed to weigh 6,000,000 of tons.'

But although the Ganges may be supposed to transport a much greater quantity of mud, even according to its size, than any other river, still there can be little doubt but Major Rennell very far over-rated the quantity of solid matter its waters contained. The Rhine when most flooded, has been computed to contain one part of mud in a hundred of water, and Sir George Staunton by several observations, calculated that the water of Yellow River, in China, contained earthy matter in the proportion of one part to two hundred. In this proportion he estimated that the waters of that river brought down 48,000,000 of cubic feet of solid matter daily.

According to the calculations of Manfredi, the celebrated Italian hydrographer, the average amount of sediment in all the running streams on the globe, is one part in 175. From such data, he estimates that it would take a thousand years to raise the general bed of the sea a single foot, provided none of this sediment was thrown back again upon the shores.

From what has been stated, the reader will observe that