VALUE OF DELTA IL ARBORS 1 6 



o 



a harl)or arc found where a large river enters the sea. Ordi- 

 narily the i)assagc of the stream from the land to the deep 

 takes place through a considerable accumulation of detritus 

 which has been brouglu down by tlie stream and spread out 

 in the form of a delta, such as exists at the mouth of almost 

 all the great riv^ers of the world. These delta ports, as we 

 may term them, w^ere among the first to be used for marine 

 commerce, and remain among the most important harbors in 

 the world. Their commercial value is peculiarl)- great, for 

 the reason that they are always connected with an extensive 

 area of more or less navigable river waters which afford a 

 natural way by which the materials of commerce may l)e con- 

 veyed to and from the interior parts of the country. Thus, 

 in the case of the Mississippi system of waters, shores, hav- 

 ing an aggregate extent of tens of thousands of miles, are 

 accessible to the delta port at its mouth. The navigable 

 w'aters of the Amazon are of yet greater extent. There are 

 in the world at least a dozen of these delta ports w^hich, 

 from their commercial importance, are or in time will be 

 ranked as havens of the first order. 



Along with their advantages delta harbors exhibit certain 

 grave defects. While the water in the channels which are 

 well within the area of the delta is usually deep (and this 

 for the reason that the motion of the stream keeps the 

 passage clear), the entrance to the river channel is commonly 

 made difficult by a widespread deposit of mud which stretches 

 for some niiles seaward beyond the mouth of the stream. 

 The formation of this outlying fringe of mutl fiats is brought 

 about in a manner which can be readily understood. When 

 the river waters enter the sea they are no longer under the 

 influence of the current of the stream which bore them on ; 



