LONG ISLAND VEGETATION 



195 



The zone of drift which is submerged even at low tide will be 

 termed the Surbmerged Beach. The Lower Beach is the portion 

 worked over by the summer waves and corresponds closely with 

 the area between the lowest and highest summer tide lines. Dur- 

 ing the storms of winter the waves attain a still higher level and 

 define a third division, the Middle Beach. The Upper Beach lies 

 beyond the action of the sea. It is present only where aggrada- 

 tion is or has been the prominent process. It is here that the 

 dunes begin their development. 



THE MARINE SUBMERGED BEACH 



The submerged beach as above defined may be further divided 

 for the convenience of description, according to the type of grada- 

 tion locally dominant. Owing to the irregularity of the coast 

 line the alternation of areas dominated respectively by aggrada- 

 tion and degradation takes place at rather frequent intervals as 

 one passes along the strand. Where erosion is strong and large 

 materials are handled the conditions for plant life are very differ- 

 ent from those where fine materials alone are carried and the 

 active process is deposition. The former situations are usually 

 found at the bases of headlands, the latter more often in the bays 

 and harbors. Between these physiographic extremes every pos- 

 sible variation may be found. The former will be designated the 

 Exposed Submerged Beach, and the latter the Protected Sub- 

 merged Beach. 



EXPOSED SUBMERGED BEACH 



The Laminaria Formation. The greater part of the beach 

 along tjie Sound which is submerged belongs in this category. 

 The presence of large rocks which are not continually moved 

 determine to a large extent whether-the vegetation shall consist of 

 anything more than the microscopic forms. Even if the larger 

 forms of red and brown algae start to develop on sand and gravel 

 areas, movement of the component rock fragments destroys them, 

 or owing to increased buoyancy the pebbles rise to the water's 

 surface and are sooner or later cast on shore. Alicroscopic forms 

 of green and bluegreen algae however do maintain a precarious 

 existence even in these extreme conditions. 



