424 



DELTAS OF THE PO AND ADIGE. 



[Ch. XVIII. 



river. 



increasing expense and 



their capacity being thereby diminished, it is necessary i n 

 order to prevent inundations in the following spring, to ex- 

 tract matter from the bed, and to add it to the banks of the 



Hence it happens that these streams now traverse 

 the plain on the top of high mounds, like the waters of 

 aqueducts, and at Ferrara the surface of the Po has become 

 more elevated than the roofs of the houses."* The magnitude 

 of these barriers is a subject of 

 anxiety, it having been sometimes found necessary to give 

 an additional height of nearly one foot to the banks of the 

 Adige and Po in a single season. 



The practice of embankment was adopted on some of the 

 Italian rivers as early as the thirteenth century ; and Dante, 

 writing in the beginning of the fourteenth, describes, in the 

 seventh circle of hell, a rivulet of tears separated from a 

 burning sandy desert by embankments 'like those which, 

 between Ghent and Bruges, were raised against the ocean, or 

 those which the Paduans had erected along the Brenta to 

 defend their villas on the melting of the Alpine snows. 5 



Quale i Fiamminghi tra Guzzante e Bruggia, 

 Temendo il fiotto die in ver lor s' avventa, 

 Fanno lo schermo, percbe il mar si fuggia, 

 E quale i Padovan lungo la Brenta, 



Per difender lor ville e lor castelli, 



\nzi che Chiarentana il caldo senta 



Jr. 



Inferno, Canto xv. 



In the Adriatic, from the northern part of the Gulf of 

 Trieste, where the Isonzo enters, down to the south of 

 Ravenna, there is an uninterrupted series of recent acces- 

 sion of land, more than 100 miles in length, which within 

 the last 2,000 years have increased from two to twenty miles in 

 breadth. A line of sand-bars of erreat length has been formed 



R ««, „ OOTO xoi w « u Vi uxxxo K ~*x, — ide ot 

 which are lagunes, such as those of Venice, and the large 

 lagune of Comacchio, 20 miles in diameter, 

 posited mud brought down by the 



nearly all along the western coast of this gulf, inside 



Newly de- 

 streams is continually 

 lessening the depth of the lagunes, and converting part of 



t The Isonzo, Tagliamento, Piave, 



f See De Beaumont, Geologie Pra- 

 tique, vol. i. p. 323. 1844. 



them, into 



* Prony, see Cuvier, Disc. Prelim. 

 p. 146. 



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