THE SURFACE OF THE GLOBE. 83 



" About the middle of the twelfth century, the great waters of the 

 Po passed across the dykes which restrained them on the left side of 

 the coast, near the small city of Ficarolo, situated nineteen thousand 

 metres (nearly twelve miles) north-west of Ferrara, and, spreading 

 themselves over the northern territory of Ferrara and the Polesine of 

 Rovigo, flowed into the two above-mentioned canals of Mazzorno and 

 Toi. It is well known that the labour of man has had much to do in 

 effecting this diversion of the waters of the Po ; and historians who 

 have mentioned this remarkable fact only differ in the detail. The 

 tendency of the river to follow the new tracks made for it becoming 

 daily more and more powerful, the two branches of the Volano and the 

 Primaro rapidly decreased, and were in less than a century reduced 

 nearly to the state in which they now are, and the main channel of the 

 river was formed between the mouth of the Adige and the place now 

 called Porto di Goro. The two canals becoming inadequate, new ones 

 were dug ; and, at the beginning of the seventeenth century, its 

 principal mouth, called Bocco Tramontana, having approached too 

 nearly to the mouth of the Adige, it greatly alarmed the Venetians, 

 who, in 1604, dug the new bed called Taglio de Porto Viro, or Po 

 delle Fornaci, by means of which the Bocco Maestra was diverted 

 from the Adige towards the south. 



During the four hundred years which elapsed from the end of the 

 twelfth to the end of the sixteenth century, the alluvial deposites of 

 the Po gained considerably on the sea. The northern mouth which 

 flowed in past the situation of the canal of Mazzorno, and formed the 

 Ramo Tramontana, was, in 1600, twenty thousand metres (twelve 

 miles) from the meridian of Adria ; and the southern mouth, which 

 had taken the place of the canal of Toi, was at the same period seven- 

 teen thousand metres (ten miles) from that meridian ; thus the coast 

 had become enlarged nine or ten thousand metres (five or six miles) 

 to the north, and six or seven thousand metres (between three and 

 four miles) to the south. Between the two mouths of which I have 

 spoken was part of the coast, which receded a little, called Sacca di 

 Goro. 



" It was during the same interval, between the thirteenth and 

 seventeenth centuries, that the great works of the embarkments of the 

 Po were made, and a considerable portion of the western declivities of 

 the Alps was cleared away and cultivated. 



" The canal called Taglio di Porto Viro determines the progress of 

 the alluvial deposites in the great promontory formed by the mouth 

 of the Po. In proportion as their entrances into the sea are distant, 



