ELEVATED COAST 303 



landward-blown sand, together with the silt brought by the 

 streams from the mainland, may fill up the lagoon. 



The filling of these lagoons, both naturally and artificially, 

 has considerably increased the habitable land of the earth. 

 The inclosed waterway back of the sand reefs has in some 

 places rendered coastwise traffic safe and easy. It is pro- 

 posed artificially to extend and develop certain of these 

 inclosed water areas along the eastern coast of the United 

 States so as to form a protected waterway from New 

 England to the southern ports. At present the low, almost 

 featureless shore of this region, with its shifting sand bars 

 and capes, makes coastwise navigation dangerous, although 

 it is protected by many lighthouses and life-saving stations. 



The sand reefs along the southern Atlantic and Gulf 

 coasts have in some places attained sufficient width and 

 height for considerable settlements. The tidal inlet, the 

 sea-beach resort, and the commercial city with reef-pro- 

 tected harbor are natural results of receding shore lines. 

 In time the waves, by their own erosive action, will deepen 

 the bottom off shore from the reef enough to enable them 

 to attack its front. Thus they will drive it back over the 

 inclosed lagoon, destroying their own work and attacking 

 the shore, which for a time they had shielded against their 

 own rapacity. 



Where the range of tide is considerable, the reefs are 

 frequently broken by inlets. Through these the water 

 of the mainland streams finds access to the sea. The shapes 

 and depths of these inlets are in some cases so rapidly 

 altered by the tidal currents that it is impossible to fore- 

 tell for any length of time where vessels can find the 

 best channel. Thus the inlets must be left uncharted and 

 local pilots relied upon. Bars which cannot be crossed 

 except at high tide often make moon time, not sun time, 

 the determining factor in the sailing schedules of vessels 



