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Ch. XVIIL] 



DELTAS OF THE PO AND ADIGE. 



425 



Brenta, Adige, and Po, besides many other inferior rivers, 

 contribute to this advance of the coast-line and to the shal- 

 lowing of the lagnnes and the gulf. 



The Po and the Adige may now be considered as entering 

 by one common delta, for two branches of the Adige are con- 

 nected with arms of the Po, and thus the principal delta has 

 been pushed out beyond those bars which separate the 

 lagtmes from the sea. The rate of the advance of this new 

 land has been accelerated, as before stated, since the system 

 of embanking the rivers became general, especially at that 



mean 



point where the Po and Adige enter. The waters are no 

 longer permitted to spread themselves far and wide over the 

 plains, and to leave behind them the larger portion oi 

 sediment. Mountain torrents also have become more turbid 

 since the clearing away of forests, which once clothed the 

 southern flanks of the Alps. It is calculated that the 

 rate of advance of the delta of the Po on the Adriatic 

 between the years 1200 and 1600 was 25 yards or metres a 

 year, whereas the mean annual gain from 1600 to 1804 was 



70 metres.* 

 Adria was a seaport in the time of Augustus, and had, in 



ancient times, given its name to the gulf; it is now about 

 twenty Italian miles inland. Ravenna was also a seaport, 

 and is now about four miles from the main sea. Yet even 

 before the practice of embankment was introduced, the 

 alluvium of the Po advanced w ith rapidity on the Adriatic ; 

 for Spina, a very ancient city, originally built in the district 

 of Eavenna, at the mouth of a great arm of the Po, was, so 

 early as the commencement of our era, eleven miles distant 

 from the sea.f 



But although so many rivers are rapidly converting the 

 Adriatic into land, it appears, by the observations of M. Mor- 

 lot, that since the time of the Romans, there has been a 

 general subsidence of the coast and bed of this sea in the 

 same region to the amount of five feet, so that the advance of 

 the new-made land has not been so fast as it would have been 



remained 



The signs of 



* Prony, cited by Cuvier, Discours. 

 Prelimin. 



f Brocchi, Conch. Foss. Subap. vol. i. 

 p. 118. 



