Essay on the Theory of the Earth

by baron Georges Cuvier

To the east of the lagunes, and north from the city of Este, we find the Euganian mountains, or hills, forming, in the midst of a vast alluvial plain, a remarkable isolated group of rounded hills, near which spot the fable of the ancients supposes the fall of Phæton to have taken place. Some writers have supposed that this fable may have originated from the fall of some vast masses of inflamed matters near the mouths of the Eridanus, that had been thrown up by a volcanic explosion; and it is certain that abundance of volcanic products are found in the neighbourhood of Padua and Verona.

The most ancient notices that I have been able to procure respecting the situation of the shores of the Adriatic at the mouths of the Po, only begin to be precise in the twelfth century. At that epoch the whole waters of this river flowed to the south of Ferrara, in the Po de Volano and the Po di Primaro, branches which inclosed the space occupied by the lagune of Commachio. The two branches which were next formed by an irruption of the waters of the Po to the north of Ferraro, were named the river of Corbola, Longola, or Mazzorno, and the river Toi. The former, and more northern of these, received the Tartaro, or canal bianco, near the sea, and the latter was joined at Ariano by another branch derived from the Po, called the Goro river. The sea-coast was evidently directed from south to north, at the distance of ten or eleven thousand metres[388] from the meridian of Adria; and Loreo, to the north of Mesola, was only about 2000 metres[389] from the coast.

Towards the middle of the twelfth century, the flood-waters of the Po were retained on their left or northern side by dikes near the small city of Ficarolo, which is about 19,000 metres[390] to the north-west of Ferrara, spreading themselves southwards over the northern part of the territory of Ferrara and the Polesine of Rovigo, and flowed through the two formerly mentioned canals of Mazzorno and Toi. It seems perfectly ascertained, that this change in the direction of the waters of the Po had been produced by the effects of human labours; and the historians who have recorded this remarkable fact only differ from each other in some of the more minute details. The tendency of the river to flow in the new channels, which had been opened for the more ready discharge of its waters when in flood, continually increased; owing to which the two ancient chief branches, the Volano and Primaro, rapidly decreased, and were reduced in less than a century to their present comparatively insignificant size; while the main direction of the river was established between the mouth of the Adige to the north, and what is now called Porto di Goro, on the south. The two before-mentioned canals of Mazzorno and Toi becoming insufficient for the discharge, others were dug; and the principal mouth, called Bocco Tramontana, or the northern mouth, having approached the mouth of the Adige, the Venetians became alarmed in 1604; when they excavated a new canal of discharge, named Taglio de Porto Viro, or Po delle Fornaci, by which means the Bocco Maestra, was diverted from the Adige towards the south.

During four centuries, from the end of the twelfth to that of the sixteenth, the alluvial formations of the Po gained considerably upon the sea. The northern mouth, which had usurped the situation of the Mazzorno canal, becoming the Rama di Trimontana, had advanced in 1600 to the distance of 20,000 metres[391] from the meridian of Adria; and the southern mouth, which had taken possession of the canal of Toi, was then 17,000 metres[392] advanced beyond the same point. Thus the shore had become extended nine or ten thousand metres[393] to the north, and six or seven thousand to the south[394]. Between these two mouths there was formerly a bay, or a part of the coast less advanced than the rest, called Sacca di Goro. During the same period of four hundred years previous to the commencement of the seventeenth century, the great and extensive embankments of the Po were constructed; and also, during the same period, the southern slopes of the Alps began to be cleared and cultivated.

The great canal, denominated Taglio di Porto Viro, or Po delle Fornaci, ascertains the advance of the alluvial depositions in the vast promontory now formed by the mouths or delta of the Po. In proportion as their entrances into the sea extend from the original land, the yearly quantity of alluvial depositions increases in an alarming degree, owing to the diminished slope of the streams, which was a necessary consequence, of the prolongation of their bed, to the confinement of the waters between dikes, and to the facility with which the increased cultivation of the ground enabled the mountain torrents which flowed into them to carry away the soil. Owing to these causes, the bay called Sacra di Goro was very soon filled up, and the two promontories which had been formed by the two former principal mouths of Mazzorno and Toi, were united into one vast projecting cape, the most advanced point of which is now 32,000 or 33,000 metres[395] beyond the meridian of Adria: so that in the course of two hundred years, the mouths or delta of the Po have gained about 14,000 metres[396] upon the sea.

From all these facts, of which I have given a brief enumeration, the following results are clearly established.

First, That, at some ancient period, the precise date of which cannot be now ascertained, the waves of the Adriatic washed the walls of Adria.

Secondly, That, in the twelfth century, before a passage had been opened for the waters of the Po at Ficarrolo; on its left or northern bank, the shore had been already removed to the distance of nine or ten thousand metres[397] from Adria.