THEORY OF THE EARTH. 127 



ber of places, which were situated, six or eight 

 hundred years ago, at the edge of the sea or of 

 large pools, are now several miles distant from 

 the water. 



Any one may observe in Holland and Italy, 

 with what rapidity the Rhine, the Po, and the 

 Arno, since they have been confined within dikes, 

 raise their beds, advance their mouths into the 

 sea, forming long promontories at their sides ; 

 and judge, from these facts, how small a number 

 of ages was required by these rivers to deposit the 

 low plains which they now traverse. 



Many cities, which were flourishing sea-ports 

 at well known periods of history, are now some 

 leagues inland ; and several have even been ruin- 

 ed, in consequence of this change of position. 

 The inhabitants of Venice find it exceedingly 

 difficult to preserve the lagunes, by which that 

 city is separated from the continent ; and not- 

 withstanding all their efforts, it will be inevitably 

 joined to the mainland *. 



We know, from the testimony of Strabo, that 

 Ravenna stood among lagunes in the time of Au- 

 gustus, as Venice does now ; but at present Ra- 

 venna is a league distant from the shore. Spina 



* See M. Forfait's Memoir on the lagunes of Venice, 

 inserted in the Mem, de la Classe Phys. de 1'Institut, t. v. 

 p. 213. 



