DELTAS IN THE SEA.

Accumulations in the Baltic. The question whether the waters of the Baltic sea have been sinking, or whether they have remained stationary, has been a subject of controversy since the middle of the last century. Celcius, a Swedish astronomer, attempted to prove that the waters of this sea had suffered a depression at the rate of about forty-five inches in a century, from the earliest times. He contended that the proof of this change rested not only on modern observations, but also on the authority of the ancient geographers, who stated that Scandinavia, now a peninsula, was formerly an island. But most of the arguments of Celcius and his followers show that they did not sufficiently distinguish between the shallowing of the water by the deposition of sediment, and the actual lowering of the sea. It appears that the sinking of the waters, on which estimates were chiefly made, were at the mouths of rivers, and in bays, where in the one case inland sediment might be expected, and in the other where loss of depth might be occasioned by the shifting of sand bars by the current of the sea. But the facts stated concerning the gradual conversion of the Gulf of Bothnia into dry land merit more attention. Thus it was shown that at Pitea, half a mile of land had been gained in forty-five years, and that at Lulea a mile of ground had been added in twenty-eight years. Ancient ports on the same coast had become inland cities. Considerable portions of the gulf were also shown to have become three feet shallower in the course of fifty years-many old fishing grounds had been changed into dry land, and small islands had been joined to the continent. Besides these changes, it was asserted that along the coast of West. Prussia, and Pomerania, anchors, and the hulls of old ships, had been discovered far inland.

But since it was possible that all these facts might be accounted for by the accumulation of land, instead of the depression of the waters, Celcius derived a stronger argument still for his theory from the exposure of certain insular rocks in the gulf of Bothnia, which were once entirely covered by water. These rocks, it was shown,

had risen in the course of a hundred and fifty years, from below the water to the height of eight feet above its sur

face, and there they stood, the most certain and permanent of all witnesses, that the sea was so much lower than formerly. To this it was opposed, that this island consisted of sand and drift stones, and that during great tempests, not only more sand, but additional stones, also, were thrown upon it. Besides this, icebergs, heavily laden with stones and rocks, sometimes floated in this sea, when the ice was breaking up in the spring, and the fact that this low island had gradually increased in height, was readily accounted for by supposing that the stranded ice fields had forced these stones above the level of the water, where of course they would remain after the ice was melted away.

This question, about which volumes were written in the course of half a century, was finally settled by a curious, but conclusive proof, brought forward by the opposers of Celcius. On the Finland side of the Baltic, there grew, close to the water's edge, some large pine trees. Some of these were cut down, and by counting the concentric rings of annual growth, it was found that they had stood there four hundred years. Now according to Celcius, the sea had sunk fifteen feet during that period, so that were this the case, these trees must have commenced their growth in at least two fathoms of water, a thing absolutely impossible. It was also proved that the walls of several ancient castles, as those of Sonderburg and Abo, reached the edge of the water at the present day, and therefore, had the water sunk, these foundations must have originally been laid below the level of the sea. Very ample proofs from other sources have also been adduced, that the level of the Baltic has suffered no change for eight hundred, or a thousand years.

But notwithstanding the proofs are quite positive that the hypothesis of Celcius can only be substantiated by deceptive arguments, drawn from progressive accumulations of solid matter in the water; still there are many intelligent men who maintain that the waters of the Baltic are suffering a constant diminution. So lately as 1821, several Swedish officers, belonging to the pilotage department, declared in favor of this opinion. The weight of evidence is, however, entirely opposed to the theory of Celcius, and there can be little doubt but the Baltic Sea has remained at its present level from time immemorial.—Lyell's Geology, vol. 1. p. 227.

We have been thus particular in this account, that the

geological student might observe how much difficulty sometimes occurs in deciding questions of this nature, and consequently how much experience and judgment ought to be exercised before any positive opinion is advanced on some geological points, in themselves apparently of the most simple kind. The great question, also, whether the‍ waters of the ocean are diminishing, as has been maintained by several writers, is involved in the question of the Baltic; for since this sea communicates with all other seas, and oceans, its gradual depression would prove a corresponding diminution of the sea all over the earth. But from the above account there is no doubt, that the supposed sinking of the Baltic is entirely a deception, arising from alluvial accumulations brought down by rivers, and the occasional shifting of sand banks by the currents of that sea.

Delta of the Rhone in the Sea. We have seen that the Rhone deposits large quantities of sediment in the lake of Geneva, and have noticed with what crystalline transparency the waters of that lake are discharged to continue the same river towards the sea. But, says Mr. Lyell, "scarcely has the river passed out of the Leman Lake, before its pure waters are again filled with sand and sediment by the impetuous Arve, descending from the highest Alps, and bearing along in its current the granitic detritus [broken rocks] annually carried down by the glaciers of Mount Blanc." The Rhone, also, afterwards receives vast contributions of transported matter from the Alps of Dauphiny, and the primary and volcanic mountains of central France, so that when it reaches the Mediterranean, it discolors the waters of the sea to the distance of many leagues.

The advance of the delta of the Rhone into the Sea, is proved by many circumstances, and particularly by the facts that an island described by Pomponius Mela, an ancient Latin geographer, is now far inland, and that a location which was a harbor in 898, is now three miles from the shore. It is also known that Psamodi, which was an island in 815, is at the present time six miles from the sea

As the Rhone enters the sea by several mouths, at considerable distances from each other, a large tract of country is brought within its influence, and thus besides extending the land along the shore, marshes of great extent 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 imbedded in crystalline limestone.

Thus we see that solid limestone is now constantly forming, in which are imbedded 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 cur

rent.

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 Apennines, 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; 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.

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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 .re salt except those which communicate with the prin