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. _Thirdly_, That the extremities of the promontories formed by the two principal branches of the Po, before the excavation of the _Taglio di Porto Viro_, had extended, by the year 1600, or in four hundred years, to a medium distance of 18,500 _metres_[398] beyond Adria; giving, from the year 1200, an average yearly increase of the alluvial land of 25 _metres_[399]. _Fourthly_, That the extreme point of the present single promontory, formed by the alluvions of the existing branches, is advanced to between thirty-two and thirty-three thousand _metres_[400] beyond Adria; whence the average yearly progress is about seventy _metres_[401] during the last two hundred years, being a greatly more rapid proportion than in former times. PRONY. NOTE, p. 244. _On the Universal Deluge._