18 THE OCEAN. 



creased, as is particularly the case at the mouths of 

 the Ganges and Mississippi; while from the same 

 cause the bottoms of inland seas being gradually 

 raised, the water rises in the same proportion and 

 encroaches on the land. The port of Ravenna, once 

 a rendezvous for the Roman fleets, has been filled 

 up by the deposition of the Montone, a small river, 

 so that now it is four miles from the sea. On the 

 other hand the palace of the Emperor Tiberius at 

 Capraea, on the opposite shore of Italy, is now wholly 

 covered by the water: nor are our own coasts, and 

 especially those of Holland, deficient in examples of 

 once fertile fields, which are now rolled over by the 



tide. 



» 



Much ignorance prevails respecting the depth of 

 the Ocean: in many places no length of sounding 

 line has yet been able to reach the bottom, and, 

 therefore, our conclusions must be formed from in- 

 ference or indirect evidence. Generally, where a 

 coast is flat and low, the water is shallow for a con- 

 siderable distance, slowly deepening; on the other 

 hand, a high and mountainous coast usually is 

 washed by deep water, and a ship may lie almost 

 close to the rocks. From these circumstances, as 

 well as from the various depths actually observed by 

 sounding, it is probable that the average depth of 

 the sea is not greater than the height of the land, 

 in proportion to its extent. If we were to place 

 a thick coating of wax over the bottom of a dish, 

 taking care to make a very irregular surface, with 

 cavities and prominences of all forms and sizes, we 

 should probably have a fair idea of the solid surface 



