236 BERTHA'S VISIT TO HER 



the mouths of the Ganges, the Nile, the Mis- 

 sissippi, the Amazons, and other great rivers; 

 and an evident change has been effected by 

 these means in many sea-coast countries, of 

 which there are innumerable instances. 



The overflowing of the Rhine, the Arno, and 

 the Po, formerly dispersed the soil they carried 

 down over the neighbouring land ; but ever since 

 it has been confined within dykes, their de- 

 posits have not only elevated the beds of these 

 rivers, but are also rapidly pushing forward their 

 mouths into the sea. The low alluvial plains 

 through which they run were themselves pro- 

 duced by ancient deposits ; and the progress of 

 this continually increasing formation may be 

 easily estimated from various historic records. 

 From Strabo we learn that Ravenna was situated, 

 in the time of Augustus, at the head of a bay 

 connected with the Adriatic, and that it had then 

 a good harbour ; yet it is now three miles from the 

 coast. By comparing the old maps with the 

 present state of the Duchy of Ferrara, which is 

 flooded annually by the Po, it appears that the 

 coast has gained from the sea 14,000 yards in 

 breadth since the year 1604, giving an average 

 of sixty yards for its advance per annum. And 

 the town of Adria, which in ancient times was a 

 sea-port, is now sixteen miles inland ! 



The same causes have produced similar effects 

 along the branches of the Rhine and Maese; 



