I 62 SEA AND LAND 



sion of heavy waves ; it must be provided with a channel of 

 sufficient depth leadin^^ from the ancliorage to the open 

 water ; the phice where the ships may He needs to be so 

 located that they may readily dischari^e and receive cargoes, 

 and the landing must be convenient of access to the internal 

 commercial routes of the district wherein it lies. When 

 these conditions are satisfied the haven in question is likely 

 to have a measurable importance, but many other conditions 

 have to be met before it will be entirely fit for commerce. 

 The sheltered waters of sufficient depth sliould afford good 

 anchorat^e ground and be roomy enough safely to accommo- 

 date many ships. The way of access from the sea should be 

 deep and direct ; it should, moreover, not be the seat of very 

 strong river or tidal currents, for the reason that such streams 

 are likely to put vessels in jeopardy. The shore near the 

 harbor should not be exposed to great masses of moving 

 sand, for these drifting with the currents are likely to endan- 

 ger the passage to the sea or by frequent changes to confuse 

 navigators. The refuge should be exempt from closure or 

 serious emljarrassment by ice. However good it may other- 

 wise be, such obstruction, even if temporary, very much 

 affects the value of a port. 



We shall now proceed to consider the physical conditions 

 which lead to the formation, preservation, and destruction of 

 havens. In the treatment of the subject we shall naturally 

 be led to a classification of these basins, based upon the cir- 

 cumstances of their origin. We shall also be led to group in 

 due order the forms of energy which operate to preserve or 

 destroy ports, and the measure in which these actions may 

 be affected by the care of man. 



The simplest condition which leads to the institution of 



