Sidor som bilder
PDF
ePub

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 alluvial 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

[ocr errors]

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 Ravenna 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 have not, in short, a single document of any sort to prove,

that the marsh land which extended from Ravenna to Aquileia, or rather, as some think, to Altino, was covered with salt water; whereas many may be brought forward to show, that the greater part of it has been overflowed by rivers. The Po, above all the rest, contributed to inundate a great tract of it; and attempts were made, at a very early period, even in the time of the Etrurians, to recover the land that had been encroached upon by its waters, by cutting several canals near its mouth, in order that it might discharge itself more quickly into the sea. Of the seven mouths of this river, two only belong to it naturally, as Cellarius has satisfactorily shown: all the rest are artificial cuts. p. 112.

There are, however, undoubted proofs of the Adriatic having, in some situations, extended further inland than it does at present. Adria, Ravenna, and Spina were at one time sea-ports: but the first of these places is now about twenty miles inland; the second about four miles; and Spina, which was built at the mouth of one of the branches of the Po, was, at the beginning of the Christian era, eleven miles from the sea-coast. Mesola was built close to the sea in 1581 by Alphonso II. Duke of Ferrara; in 1599 its eastern wall was already two-thirds of a mile distant from it; and, in 1750, it stood from six to seven miles inland.

But, on the other hand, Brodolo stood in the same situation seventeen centuries ago that it does now; for Pliny speaks of it as a port of the Laguna, where some rivers emptied themselves into the sea: the same may be said of Chioggia, Fossa Clodia, which was then a port at the mouth of the Brenta and Bacchiglione. Altino, built like Ravenna, in the midst of salt marshes, is still (or rather the place where it stood) washed by the Laguna di Cona, at least in high tides. Padua, in the time of Livy, was seventeen miles from the shore, as it is now. Dolomieu, on the authority of Strabo, has said, that about the beginning of the Christian era, an arm of the sea reached the walls of that city: But he must have misunderstood that author; for Strabo, so far from asserting that the Adriatic extended to Padua, says, that, to reach the sea, they sailed down the Brenta, then called the Meduacus, which discharged itself into the sea at the great port of the same name, and which is now called Malamocco. To this may it be added, that the description given by Livy himself (which is the most ancient document that can be brought forward) of the state of the Laguna, and of the appearance of the country around Padua, perfectly applies at the present day. "Penitus ad littora Venetorum pervenit: ibi expositis paucis, qui loca explorarent, quum audisset, tenue prætentum littus esse; quod transgressis stagna ab tergo sint, irrigua æstibus maritimis; agros haud procul proximos campestres cerni; ulteriora colles. This shore, as all critics agree, was that of Malamocco, which appears exactly like a narrow strip of land: The salt marshes were the Lagune; the fields, those between Chioggia and Fusina; and the hills, the Euganean Hills.'

[ocr errors]
[ocr errors]

M. Brocchi might have added the continuation of the passage he has quoted; for it proves still more distinctly the error of Dolomicu. Inde esse ostium fluminis præalti, quo circumagi naves in stationem tutam vidisse: (Meduacus amnis erat) eo invectam classem subire flumine adverso jussit. Gravissimas navium non pertulit alveus fluminis: in leviora navigia transgressa. multitudo armatorum ad frequentes agros, tribus maritimis Patavinorum vicis colentibus eam oram, pervenit. Lib. X. 2.and there are some further illustrations in the same chapter..

There does not appear to be any essential or constant difference of species in the fossil shells found in the Sub-Apennine. Hills, either in regard to the greater or less depth of the strata in which they are found, or the materials of which the strata are composed. They are not scattered confusedly through the different beds, but often appear to be distributed in families and distinct species that distribution, however, has no correspondence with the situation of the beds. Not only the shells which are found in the present sea, but those of which the prototypes are unknown, the indigenous, as well as the exotic, are found both in the marl and in the sand that lies over it. There are perhaps some exceptions, some shells which belong more particularly to the sand; but they are not such as to warrant any general deduction. All the tertiary deposits do not contain shells, there being extensive tracts where they are either wholly wanting, or are only to be traced by some scattered vestiges, although the materials composing those districts are the same as those beds which contain the fossil shells in greatest abundance.

.

There is, in general, a great analogy between the fossil shells found in different parts of Italy. The same species are found in Piedmont, in the territories of Placentia and Bologna, in Romagna, Tuscany and Puglia, and even in Calabria, as is shown by the work of Scilla. It is also remarkable, that some particular shells, the originals of which are unknown, are common in several places far distant from each other. p. 145.

The fossil shells of the Sub-Apennines may be divided into two general classes, the one comprehending the shells that are still found in the sea, the other comprehending those whose prototypes are unknown. The first of these classes may be further subdivided, by distinguishing the species found in the Adriatic and Mediterranean from those which belong to distant seas. The number of the indigenous shells is very considerable; and there are many examples of those which have been described by naturalists as peculiar to the Asiatic, African and American seas. Among the most remarkable of these, are the Bulla Ficus

« FöregåendeFortsätt »