S83 



large rivers. Consequently the alluvion, which wai 

 held suspended in their waters, was propelled to some 

 distance beyond the month of the rivers into the gulf or 

 sea ; and as the currents of the rivers were slackened, 

 the alluvion was deposited ** hy the mere action of 

 gravity/' 



Here was the commencement of those deltas which, 

 like that of the Po, were for ages scarcely perceptible. 

 But as the beds of these rivers were elevated and ex- 

 tended, the currents were still more retarded, and 

 banks were formed and extended at their sides. 



Subsequently, on the occurrence of an unusual high 

 tide, opposing and elevating the current of the river, 

 it bursts its natural bounds, and makes an irruption 

 through its banks, thus causing lateral branches, and 

 carrying the alluvion still farther on, and in different 

 directions. On the subsidence of the waters, the sands 

 are exposed to the operations of the rains and winds, 

 which in some instances have, iu the course of time, 

 with the assistance of alluvial deposites from the river, 

 filled up the canals or lateral branches. At a subse- 

 quent period, and on a like occasion, other breaches, 

 or irruptions are made through the banks, and new 

 branches are formed. In this way the work gradual- 

 ly goes on, until these new formed grounds, in time, 

 become habitable. On being located, for the conve- 

 nience of fishing or trade, and perhaps both, the inha- 

 bitants commence the operation of dyking, with a view 

 to secure themselves from the inroads of the sea, or the 

 overflowing of the river, and every instance of this 



