a cavity exists, and it is certain that steam is the moving power.

Mr. Lyell forms a theory of earthquakes on this explanation.-See Seat and Theory of Earthquakes.

seas.

DELTAS IN LAKES.

Considerable changes have taken place by causes now going on, in consequence of the deposition of earthy matter at the mouths of rivers where they enter lakes, or We have already given an account of the accumulation of land along the shores of the Adriatic, in consequence chiefly of depositions from the river Po. The quantity of matter thus carried down by different rivers, of similar magnitudes, differs exceedingly; this difference depending much on the rapidity of the stream, and its liability to overflow its banks at certain seasons.

The Lake of Geneva is

Delta of the Lake of Geneva. thirty-seven miles long, and from two to nine miles broad. The Rhone enters at one end of this lake and the city of Geneva stands at the other. The water where it discharges itself near the city is exceedingly clear and transparent, but at the upper end it is commonly turbid, in consequence of the matter brought down by the Rhone.

Mr. De La Beche, after numerous soundings, found that the depth of the water in the middle of the lake was from one hundred and twenty, to one hundred and sixty fathoms; but on approaching the mouth of the Rhone, the water began to grow shallower at the distance of a mile and three quarters from that end of the lake. It may be stated therefore that the strata annually produced by the river are about two miles in length. From soundings it has been ascertained, that in some places the deposites from the Rhone are probably from six to nine hundred feet in thickness; and from the remains of some Roman buildings on the border of the lake, Mr. Lyell judges that this accumulation has taken place within the last eight hundred years. "If," says he, "we could obtain the depth of this accumulation formed in the last eight centu ries, we should see a great series of strata, probably from

six to nine hundred feet thick, and nearly two miles in length, inclined at a very slight angle."

Mr. Lyell proposes a plan for estimating the time when the Lake of Geneva, or the Leman Lake, will become dry land by the accumulations from the Rhone.

The capacity of the lake being obtained, "it would," says he, "be an interesting subject of inquiry, to determine in what number of years the Leman lake would be converted to dry land. It would not be difficult to obtain the elements for such a calculation, so as to approximate at least to the quantity of time required for the accomplishment of this result. The number of cubic feet of water annually discharged by the river into the lake being known, experiments might be made in winter and summer to determine the proportion of matter held in suspension, or in chemical solution by the Rhone."

Such calculations, however, after all the data that could be obtained, would be exceedingly uncertain, and since the elements, proposed by the author, have not been obtained, we do not extract his speculations on this subject.

But were it ascertained exactly how much alluvial matter is carried down by the Rhone at the present day, still this would decide nothing definitely with respect to the time during which this accumulation has been forming. According to Mr. Lyell's supposition above cited, a part of the delta has formed at the rate of about a foot in a year, namely, from six to nine hundred feet in eight hundred years. Now allowing that the Rhone has, on an average, deposited a foot of matter a year in the lake, and has continued to do so ever since the deluge, then the accumulation ought to be at least four thousand feet thick, which would long ago have filled up the Leman lake, and made it solid ground. The phenomena of this lake, therefore clearly shews that either it has not received the Rhone for so many years, or if so, that its waters contained less solid matter anciently than at present. In either case, it is quite certain that no argument can be derived from the present condition of this delta, in favor of the high antiquity of the present form of the earth. But on the contrary, if any conclusions can be drawn from this source, they are in direct coincidence with the idea that the present order of things are of recent origin, and therefore in confirmation of the truth of the sacred history of the deluge.

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 twentyeight 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. i. 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.

We have seen that the

Delta of the Rhone in the Sea. 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