igS SEA AND LAND 



aloni^ the shores, it is very difficult to secure any permanent 

 increase in depth of water Ijy any appHcation of engineering- 

 skill. 



A century ago, when trading ships had less than half their 

 present tonnage, rarely drawing more than hfteen feet of 

 water, lagoon harbors were excellently suited to the needs of 

 commerce ; but at the present time, when many vessels trad- 

 ing with foreign countries have a draft of twenty feet or 

 more, such ports have become less useful, and have to be 

 bettered by engineering appliances or they are likely to pass 

 out of use except by relatively small coasting vessels. As 

 the greater part of the harbors between Norfolk and the Rio 

 Grande are of the lagoon type, the question as to the im- 

 provability of these ports is clearly of very great importance. 



The group of embayments which we have to consider 

 under the head of sand-spit harbors, are, as regards their 

 origin and nature, closely related to the lagoon harbors last 

 described. They have, however, sufficient individual charac- 

 ter to deserve mention under a sei^arate head. Sand spits 

 are formed where the beach materials of a shore are forced 

 by the prevailing direction of the waves or currents to travel 

 in a more or less continuous manner in a particular direction 

 along the coast. Except for careful observations, this move- 

 ment may not be detected until the materials attain a point 

 where there is a more or less definite bay extending into the 

 mainland. At such a point the sands, instead of flowing back 

 into the reentrant, may be built out in the form of a long spit 

 which grows steadfastly at its outer end until it may project 

 more or less completely across the mouth of the opening. 

 Excellent examples of these spit beaches are traceable along 

 our American shore from northern Massachusetts to Mexico. 



