FREER INS FITUTE -OF SCIENCE 
VEGETATION OF SOUTH FLORIDA 
63 
SEA STRAND FORMATIONS 
The sea beaches and the undulating surface back of them in South 
Florida consist of two kinds of materials, as previously indicated.  Silicious 
sand is the material which forms the beaches and dunes of the coast north 
of Key Biscayne, while Soldier Key and the islands south of it have their 
sea beaches formed of calcareous sand, which represents the ground-up 
particles of coral, shells and calcareous seaweeds. The hills formed by wind- 
blown silicious sands may reach considerable elevation, while those of cal- 
careous sand are usually low, because the particles, through the action of rain 
water, are often cemented together and are not blown about by the fickle winds. 
Sea Beach Plamt Formation.—The observations which follow are based 
on an examination of the beaches of silicious sand in South Florida. Little 
or no study was made of the flora of the calcareous beaches of the keys, the 
vegetation of which for the most part is excluded from this account. The 
sand which forms the beaches is a medium fine quartz sand and rather angular. 
Its color varies from gray, the prevailing tint, to pale yellow, to light reddish 
brown. We may distinguish three subdivisions of the beach, viz., the lower, 
or front, beach, the middle beach and the upper beach. The lower beach is 
without visible vegetation, as it is covered and uncovered by the rising and 
falling of the tides, and is exposed to the full force of the breakers, when the 
surf is at all rough. It slopes gradually seaward with a gentle declination, 
so that the bathing is usually safe. This is the submerged beach. The middle 
beach is characterized by the material that has been cast ashore by the higher 
tides. It is covered with a miscellaneous flotsam and jetsam, such as sea- 
weeds, fruits, and seeds, driftwood, broken shells, animal remains, and the 
like. The lower part of the middle beach is without rooted plants, but if it is 
wide, we find its upper levels invaded by plants that are normally found as 
tenants of the upper beach, which stretches to the foot of the dunes. The 
middle beach and the upper beach sand is usually dry when the tide is out, 
but the lower beach sand shows the presence of a considerable amount of in- 
terstitial water which is demonstrated when the foot is pressed into sand 
which whitens, owing to the expulsion of water, while as soon as the foot is 
lifted the original gray color is restored. A study of the beach flora of sub- 
tropic Florida naturally resolves itself into an examination of the flora of the 
upper beach. Observations were made at five widely separated localities, 
viz., the beaches of Anastasia Island off St. Augustine, Ormond Beach, Ocean 
2 
| 
| 
| 
| 
| 
| 
