54 MARINE FISHERIES OF NORTH CAROLINA 



after the manner described by Shaler; but inlets are more commonly re- 

 opened during exceptional storms by vigorous wave erosion. A bar exposed 

 to the waves of an occasional great storm may thus be breached, where one 

 less exposed would remain intact. 



"On the other hand, it matters little how many inlets may be opened by 

 the waves, longshore currents will soon close all except those kept open by 

 tidal currents reinforced by outflowing land waters. If the tidal range is such 

 as to generate currents capable of maintaining two inlets of a given breadth 

 through a certain bar, and storm waves cut two additional inlets, the tidal 

 waters will for a time flow through the greater number of openings with 

 decreased velocities. Longshore currents will therefore dominate the tidal 

 currents at the inlets, until deposition has narrowed all of the inlets, or closed 

 two of them (often the older ones), leaving the other two of the required 

 breadth and thereby re-establishing a condition of equihbrium. Or, if a storm 

 drives waves obliquely upon a coast in such manner as greatly to accelerate 

 the longshore transportation of debris, all the inlets through a bar may be 

 closed by excessive deposition in spite of tidal currents. Once the inlets are 

 closed, the tidal currents cease to exist; and the inlets will remain closed until 

 storm waves or some other agency makes new breaches through the bar. In 

 general we may say that waves tend to make inlets, tidal currents to preserve 

 them, and longshore currents to close them. 



"That the supply of debris brought by longshore currents may be more 

 important than differences of tidal range in determining the number of inlets 

 through a bar, is apparent from a study of certain offshore bars which are 

 supplied with debris derived from headlands to which the bar is at one end 

 attached. Let us deduce the conditions which theoretically should charac- 

 terize offshore bar and lagoon development when the bar is attached to a 

 headland, and longshore currents move from the headland toward the further 

 extremity of the bar. 



"In the first place, it is evident that while wave currents may remove much 

 material from the face of the bar and transport it seaward to deeper water, 

 near the headland the loss may be more or less completely made good by new 

 debris brought from the adjacent source of supply by longshore currents. 

 The effect of this accession of debris is two-fold; the bar withstands the 

 normal tendency of the waves to drive it landward since the waves have all 

 they can do to take care of the new material continually being added to its 

 face ; and for the same reason the waves are less apt to cut inlets through the 

 bar, while longshore currents utilize the abundant debris to seal up such inlets 

 as may occasionally be formed. Accordingly we should expect a tendency for 

 lagoons to be broad and bars to be continuous in the vicinity of headlands. 



"Toward that end of the bar most remote from the headland, conditions 

 are very different. The debris from the headland has been ground fine in the 



