FORM OF NANTASKET BEACH 



167 



the island (Fig. 2), several types of tying may result under different 

 conditions. If there is no pronounced current action except the 

 on-shore and off-shore tidal currents and the movements of the water 

 due to waves coming from the east, simple backward tying may 

 result (a) . Under the same conditions as those just outlined, provided 

 that the shallowing of the water inland is favorable, the material 

 eroded from the head of the island may be drifted backward but at 



the same time northward and 

 southward in curving lines 

 along a zone where the water 

 is of such depth as to favor 

 deposition before reaching 

 the bay head. Similar de- 

 posits from the headlands 

 would meet those from the 

 island, and lateral tying by 

 curved bars would result (h). 

 These bars might then be 

 prograded, as explained on a 

 previous page, until they 

 formed a nearly straight 

 shoreline between the island 

 and the headlands. If the 

 tidal action were fairly strong, 

 the bars from the island and 

 headlands might not join, 

 leaving each portion as a 

 spit, possibly more or less 

 irregular in form, at its free 

 end (c). If a pronounced 'longshore current existed, the waves still 

 coming from the east, the material eroded from the island by wave 

 action might be transported by the current from the island toward 

 the headland, building a bar which would eventually tie the island to 

 the mainland id) . In a similar manner a bar built northward from 

 the southern headland might effect the tying of the island to the 

 mainland {e). A sufficiently strong tide might prevent the tying in 

 either case by maintaining a tidal inlet. But if the tying were effected, 



c ::e 



Fig. 2 



