is 1330 feet above Turin, and 2064 feet above the level of the Mediterranean.

In many parts of Italy are found travertini, tufi, and other deposits, containing fresh-water shells, lying upon or alternating with marine strata, and even covering volcanic substances. The plain of Sarteano in the Valdichiana Sanese, and the country round Staggia and Poggibonzi, are covered by a mass of tufa full of these shells. In the neighbourhood of Montalceto, in the Crete Sanesi, in Valdelsa, at Prata in the Maremma Toscana, there are entire hills of travertino; and the Rock of Tivoli over which the Teverone is precipitated, and the subjacent plain, in which the Solfatara is situated, are composed of this same

stone,

In the third section of the work, a few pages are occupied with some slight notices on the analogy between the structure of the Sub-Apennine hills, and the tertiary deposits of other countries. The instances the author chiefly dwells on, are the coun try round London, as described by Parkinson, and the Essay on the Mineralogy of the neighbourhood of Paris, by Cuvier and Brongniart. The London gravel and blue clay he considers very similar to the siliceo-calcareous sand and blue marl of the Sub-Apennine hills. There is undoubtedly a great resemblance, not only in the mineralogical characters of the London clay and the marl of Italy, but also many of the substances that accompany them are common to both, There seems, however, to be a great dissimilarity in the fossil shells they contain; and in geological position, they are widely different. The vast series of secondary strata that intervene between the London clay. and the Lyas limestone of England, which is perhaps the first in the series of strata, downwards, that can be said to resemble the limestone of the Apennines, appears to be wholly wanting in Italy; a remarkable circumstance, and not very consistent with the doctrine of universal formations. The analogical structure of the Paris Basin seems to go no farther, than that it is of a tertiary formation, and that it contains sand and clay; for the fossils and the different beds are in the greater number of instances totally different. The chief part of this section is occupied by an examination of the changes which the great Vale of Lombardy has undergone from the deposition of alluvial matter.

This extensive valley, which appears like a great gulf sur rounded by the Alps and Apennines, is totally different in physical structure from all other parts of Italy. It is a uniform plain, scattered over with rounded fragments of secondary limestone, mixed with others of primitive rocks; such as granite, micaceous schistus, &c. which are thickly spread over the high

er parts of the valley near the foot of the Alps, but gradually diminish in quantity and size as they approach the shore, when they are succeeded by a light earth, or very fine sand, forming a bed of great thickness. All along the sides of the Apennines, by Modena, Parma, Placentia, and Piedmont, there is an uninterrupted line of hills, composed of the marl containing shells; but along the Alpine boundary of the valley, this marl is only found in detached spots, separated from each other by intervals of many miles, and nowhere exists in the plain itself.

To account for the physical structure of this valley, some have imagined that the Adriatic, after having attained its present level, extended to the foot of the Alps, and that the whole of Lombardy was a vast lake, which was afterwards filled up by the materials carried down by the torrents from the mountains. This opinion, brought forward by Sabbatini in 1550, in a work, entitled-Trattato Sulla Laguna di Venezia, has been revived by Filiasi, in his book Sui Veneti Primi, in so far as he supposes that the whole of Lombardy was at one time a gulf of the sea; but, rejecting the theory of Sabbatini and others, that the waters gradually retired, in consequence of the formation of land along the line of the coast, he considers the bottom of the gulf itself to have been raised by the gravel, sand, and mud, carried into it by torrents. This theory is rejected by M. Brocchi, who insists on the improbability of the rivers of a country overflowing it to such an extent, as to cover it with water-worn blocks and fragments; and he shows, that this event could not take place in a considerable part of the country now under review, where the chief rivers pass through deep lakes, in which they must have left all the greater fragments of rocks that they might have brought down from the Alps. He conceives, that the rolled masses now found in the upper part of the valley are the ruins of rocks which formerly occupied the space of the valley itself, broken down by a great irruption of the sea; a catastrophe that must have taken place prior to the deposition of the shelly marl of the Sub-Apennines; because the fragments chiefly belong to the primitive rocks, and they are found in some situations under the marl. To the obvious question, how the sea, which held the materials of the Sub-Apennine hills suspended in its waters, did not deposit them equally over this mass of ruins, but left them so partially on one side of the gulf, and so regularly on the other, M. Brocchi replics, by supposing the existence of a great current along the foot of the Alps, which, combined with the agitation produced in the sea by the waters of the Po, the Ticino, the Adda, the Adige, and the other rivers, prevented the precipitation of the materials on that side, but left them to settle in the calmer waters on the

sides of the Apennines: And, to show that this is not a mere gratuitous assumption, he adduces the following observations on the present state of the Adriatic.

Olivi, in his sketch of the topography of the Adriatic gulf, has shown that the nature of its bottom is different in different situations; there being in some places sand, in others clay, and in some parts of it there appears to be a naked rock. He found mud extending from Malamocco to Ancona, and continuing outwards to about half the breadth of the sea; and from thence the bottom is a solid mass of limestone, quite over to the rocky shores of Istria and Dalmatia. Having made soundings in different depths, he found that the accumulation of the loose materials corresponded with the direction and force of the currents, of which there is a very constant and considerable one, which running parallel to the shores of Dalmatia and Istria, follows the coasts of Friuli and the Marca Trivigiana, and continues its course in a southerly direction, by the Venetian terri tory and Romagna. From this Olivi concludes, that the muddy depositions must be carried by the eastern current towards the west; and that they accumulate where there is least agitation in the water.' I. 94.

Between Parezzo in Istria, and Malamocco near Venice, abont the middle of the gulph, there is a muddy bank resting upon the solid limestone, of about three miles in breadth, and extending in length to a point opposite Comacchio. Olivi observes, that, in calm weather, the water over this bank is almost stagnant; whereas on each side of it there is a continual motion, from the current already -mentioned; and, in consequence of this, the rock is laid bare on each side, where the loose materials are carried away by the current; but in the middle, where there is scarcely any sensible motion, the alluvial matter accumulates.' p. 104.

Nearly the whole of the provinces of Mantua, Modena, Ferrara, Polesina, and Padua, and particularly those places that are nearest the coast, are covered with a thick bed of fat and spungy earth. In the wells of Modena, the water springs from a bed of gravel which is mixed with marine shells; and, before coming to it, they dig to the depth of about 63 feet on an average, passing through beds of fat clay and black earth, mixed with portions of vegetables: in Polesina, and the territory of Padua, it is necessary to go to a still greater depth. Sir George Shuckburgh ascertained, that the plain of Modena is 201 feet above the level of the sea; so that, taking the average depth of the wells at 63 feet, the surface of the gravel containing marine remains is 138 feet above the present level of the Adriatic; demonstrating, that the plain of Lombardy has not been gained from the sea, since it attained its present level, by the alluviak matter carried into it from the surrounding mountains. To account for the deposition of this vast mass of clay and earth

over so great a surface, M. Brocchi supposes that there was a time when the rivers were not confined within a channel, but spread themselves wherever their waters could reach, and inundated vast tracts of country.

*The Lambro and the Olona overflowed the territory of Lodi, the Po formed vast marshes between Parma and Placentia, which were drained by Scaurus; the neighbourhood of Modena was covered with pools and reeds in the time of Augustus; and Ravenna was surrounded by stagnant water, so that it was only approached by one side. The waters of the Adige, the Po, and the other rivers, formed the Padusa and the Venetian marshes, which extended from Ravenna to Altino; a circuit, according to Pliny, of 2000 stadia. The whole of Polesina, and the territory of Ferrara, was intersected by ditches and swamps; I say intersected, because it is doubtful whether they were entirely under water; for, besides that Cluverius (though without very good authority) has asserted that the Forum Allieni of Tacitus was situated where Ferrara now stands, the Roman remains that have been dug up at Voghenza, at the distance of eight miles from that city in the direction of Comacchio, among others a marble, bearing an inscription that refers to the time of Marcus Aurelius, show that the country was at least inhabited in detached spots. To the accumulated products from this diffusion of the waters, must be added the alluvial matter that would be spread by extraordinary floods, of the destructive effects of which the historians of the middle ages have left us tremendous accounts. Paulus Diaconus gives an account of one that happened in 586, which was compared to the Deluge: Another took place about the year 1100, when the Adige swelled to so great a degree, that it overflowed its banks, and cut another channel. The alluvium of the lower parts of Lombardy underwent infinite changes, while the upper parts, from their higher level and greater slope, were as free from such changes then as they are now. P. 108.

Our author next proceeds to inquire whether the rivers, in raising the surface of the plain of Lombardy, have also extended it by their depositions along the shore. Dolomieu, who was of opinion that the sea had at one time reached as far as Cremona, and that the whole of Lombardy which lies between Cremona and the shore, had been formed by the materials brought down by the rivers, comes to this conclusion, from the resemblance of the alluvial matter found around that place, to that which the Po and other rivers now carry to the Adriatic. To support this opinion, it would be necessary to show that the surface of the first stratum of marine origin on which the alluvial matter rests, is not higher than the level of the Adriatic; and M. Brocchi proves, that this stratum at Modena, which is considerably nearer the coast than Cremona, is 138 feet above. that sea. Many Italian writers, who have inferred, from the

various passages in ancient authors, describing towns surrounded by water, and districts covered by lakes, which are now dry land, that the sea formerly extended much beyond its present limits, appear to M. Brocchi to have been led into a mistake, by supposing that to have been sea which was an inundation of fresh water.

• Amati has treated this subject at greater length than any other; and the following are his chief arguments, which, with some exercise of patience, I have extracted from a vast mass of quotations and commentaries. 1. The salt water lakes, he says, extended at one time as far as Brescello, near Reggio, because Strabo relates that Hannibal, in moving from the neighbourhood of Placentia towards Etruria, marched for three successive days across marshes; a distance that may be reckoned at about 60 miles, and might comprehend the territories of Parma, Reggio, and Modena. 2. In the time of Augustus they were contracted, but still reached as far as Sermide; for in the Itinerary of Antoninus, written about that time, the road from Este to Bologna is made to pass through that place and Modena; showing that the territories of Polesina and Ferrara were still submerged, but that the country above them could be passed over. When the sea reached to Sermide, Spina, built upon the shore 1100 years before the Christian era, was, according to Strabo, eleven miles distant from it: how much farther inland then must it not have extended, when it washed the walls of that city! It must have reached at least as far as Brescello, 3. The salt-water lakes, in the time of Justinian, had contracted still more, and did not extend beyond Argenta, situated on the Lago di Comacchio; for Procopius says, that it was possible to sail from Ra venna with the flood-tide as far inland as an active man could go in a day, which may be reckoned at thirty miles; and as he adds that the voyage might be continued from thence as far as Aquileia, he thus points out the direction of that navigable tract.

Amati always confounds, says M. Brocchi, the salt water lakes with those formed by the rivers. Strabo relates, it is true, that Hannibal found himself impeded in the marshes of Placentia: but he says distinctly, that they were formed by the Po, swollen by the Trebbia, and other rivers that flowed into it, and which were drained by Scaurus, who made navigable canals from Placentia to Parma, That the sea extended over the territories of Ferrara and Polesina in the time of Augustus, because the road from Este to BoJogna passed by Sermide and Modena, is a deduction equally arbitrary. It proves no more that these countries were overflowed by the waters of the Adriatic, than by those of the Po and the Adige, which last, even in the present day, frequently overflow their banks in those territories. That the sea, in the time of Justinian, reached as far as Argenta, may very readily be believed, for it does so at present by means of the Lago di Comacchio.

We haye not, in short, a single document of any sort to prove,