THEORY OP THE EARTH. 137 



has deposited alluvial formations all along the rest 

 of the coast. In the time of Herodotus, the coast 

 of the Delta extended in a straight line, and is 

 even represented in that direction in the maps con- 

 structed for the geography of Ptolemy : but since 

 then the coast has so far advanced as to have as- 

 sumed a semicircular projection into the Mediter- 

 ranean, The cities of Rosetta and Damietta, built 

 on the sea-coast less than a thousand years ago, 

 are now two leagues distant from the sea. 



We may learn in Holland and Italy, how rapidly 

 the Rhine, the Po, and the Arno, since they have 

 been confined within dikes, now elevate their beds, 

 and push forward the alluvial grounds at their 

 mouths towards the sea, forming long projecting 

 promontories at their sides ; and it may be con- 

 cluded, from this assured fact, that these rivers 

 have not required the lapse of many centuries to 

 deposit the low alluvial plains through which they 

 now flow. 



Many cities, which were flourishing sea-ports 

 in well-known periods of history, are now seve- 

 ral leagues inland, and several have even been 

 ruined by this change. The inhabitants of Venice 

 at present find it exceedingly difficult to preserve 

 the lagunes, by which that once celebrated city 

 is separated from the continent of Italy, from fil- 

 ling up ; and there can be no doubt that she will 



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