861 



ACriON OF RIVERS AND CURRENTS ON THE BOTT'^M 



OF THE SEA. 



1. Choking of Ports with Sand — Deltas, and the action of the Tide 

 upon them — The formation of Deltas may be either favoured 

 or retarded by Marine Currents according to circumstances — 

 Deltas formed in Shallow Seas— Rapid growth of the Delta of 

 the Po due to the Clearing of the south side of the Alps, and to 

 the Damming-in of the Shores of the River. 



The movements of the submarine soil are among 

 the most active causes of variation in the distribution 

 of h^nd and sea on our globe ; but they are far from 

 being the only causes of tiiis phenomenon. The rush 

 of the waters is continually causing disintegration of 

 the soil where the current is rapid, and the whole of 

 the matter thus carried in suspension is deposited 

 IV hen the waters attain a position of rest in parts 

 of the ocean where these currents cease to act. This 

 is why ports choke up, unless a strong current of 

 water can be made to flow through them. The sand 

 is deposited most I'apidly when the entrance to the 

 port follows the direction of a current parallel with 



