80 ON THE REVOLUTIONS OF 



covers the small artificial hills, on which the ancient cities were 

 founded, to a depth of several feet*. 



The Delta of the Rhone is no less remarkable for its accumulations. 

 Astruc details them in his history of Languedoc ; and, by a careful 

 comparison of the descriptions of Mela, Strabo, and Pliny with the 

 state of the places as they were at the commencement of the eighteenth 

 century, he proves, by the aid of many writers of the middle ages, 

 that the arms of the Rhone have extended themselves three leagues 

 during eighteen centuries ; that the alluvial accumulations of a similar 

 kind have been formed to the west of the Rhone ; and that many 

 places, situated six or eight centuries back on the bank of the sea 

 shore or large pools, are now many miles inland. 



Any person may observe in Holland and Italy how rapidly the 

 Rhine, the P6, and the Arno, now that they are confined within dykes, 

 raise their beds ; how their mouths approach into the sea by forming 

 long promontories at their sides ; and can judge by these facts how 

 few centuries these waves have employed in depositing the flat plains 

 which they at present traverse. 



Many cities, which at well-known periods of history were flourish- 

 ing sea-ports, are now several leagues inland ; many have even been 

 ruined in consequence of this change of situation. Venice can scarcely 

 preserve the lugunes which separate her from the continent ; and, in 

 spite of every exertion, she will one day become united to the main 

 land f . 



We learn from Strabo, that, in the time of Augustus, Ravenna was 

 amongst lagoons, as Venice now is ; and now Ravenna is a league 

 from the shore. Spina had been founded by the Greeks on the sea 

 shore ; yet in Strabo's time it was ninety stadia from it, and is now 

 destroyed. Adria in Lombardy, which had conferred its title on the 

 sea, of which it formed (during a period of more than twenty centuries) 

 the principal port, is now six leagues distant from it. Foris has even 

 reckoned it probable, that, at a period still more remote, the Euganian 

 mountains might have been islands. 



My learned brother of the Institute, M. de Prony, inspector-general 



* The the Observations on the Valley of Egypt, and on the regular increase of the 

 soil which covers it, by M. Girard, in the great work on Egypt, and Mod. Mem. v. 

 2, p. 343. On which we may remark, that Dolomieu, Shaw, and other good au- 

 thors, estimate these accumulations much higher than M. Girard. It is to be re- 

 gretted that the thickness of these layers have not been examined, either on the primi- 

 tive soil or the natural rock. 



f See the Memoir of M. Forfait on the lagoons of Venice, with Mem. de la Classe 

 Phys. de l'lnst. vol. v, p. 213. 



