THEORY OF THE EARTH. 129 



eighty, and in some places two hundred feet year- 

 ly. The Adige and the Po, are at the present 

 day higher than the whole tract of land that lies 

 between them; and it is only by opening new 

 channels for them in the low grounds, which they 

 have formerly deposited, that the disasters which 

 they now threaten may be averted. 



The same causes have produced the same ef- 

 fects along the branches of the Rhine and the 

 Meuse ; and thus the richest districts of Holland 

 have continually the frightful view of their rivers 

 held up by embankments at a height of from 

 twenty to thirty feet above the level of the land. 



M. Wiebeking, director of bridges and high- 

 ways in the kingdom of Bavaria, has written a 

 memoir upon this subject, so important as to be 

 worthy of being properly understood, both by 

 the people and the government, in all countries 

 where these changes take place. In this memoir, 

 he shews that the property of raising the level of 

 their beds is common in a greater or less degree to 

 all rivers. 



The additions of land that have been made a- 

 long the shores of the North Sea, have not been 

 less rapid in their progress than in Italy. They 

 can be easily traced in Friesland and in the coun- 

 try of Groningen, where the epoch of the first 

 dikes, constructed by the Spanish governor Caspar 

 Robles, is well known to have been in 1570. An 



