SECOND ANNUAL REPORT-SOUTHERN ERORIDA. 
199 
mense amount of limy material is supplied by the remains of marine 
organisms, the agitation of the shallow near-shore water facilitates de¬ 
position of calcium carbonate, and the effluent swamp waters contain 
organic compounds that may act as precipitants. Hence banks of marl 
form near river entrances or outsides of passages leading from lagoons, 
and where the banks are protected mangroves gain a foothold and 
interrupt the sequence of forms that would result from the unopposed 
action of waves and currents. 
Maps of the east coast show a shore line with adolescent features, 
such as cuspate forelands, well developed bay bars and long beaches 
with gentle curves. The offsets and overlaps of the bars and beaches 
show that the movement of sand is toward the south. This movement 
is very marked at Jupiter Inlet. When the bay bar at the mouth of 
the Inlet is cut through at its north end to make a navigable channel, 
the drift of the sands makes the channel travel southward, till as it 
approaches the south side of the Inlet it shoals up and the water 
flows over the bar in a shallow sheet. 
The lagoons or “rivers” of salt or brackish water back of the 
beaches are being filled by swamp growths. While the tidal swing is 
small, the extent of the lagoons, and the amount of water discharged 
at each ebb is sufficient to transport and assort lighter debris, but in 
the shaping of the coast the waves and along shore currents play the 
chief part. 
In the Bay of Florida the rocky shores of the coral islands show 
the nip of the sea, while banks and marl flats are gaining areas, and 
mangroves vigorously extend the land. Tidal currents are the prin¬ 
cipal agencies of transportation along the south side of the bay, where 
under favoring conditions currents with velocities as high as five miles 
an hour rush through the openings between the keys. Along the 
north side of the bay tidal action is much weaker and winds and cur¬ 
rents perform a proportionately larger part of the work. Wave action 
though of importance, is limited by the shallowness of the bay. 
From East Cape to North Cape extends a strip of shell sands, the 
Cape Sable foreland, that has been pushed up from the bottom by 
the waves. Tidal action is strong, there is a pronounced tide rip past 
Middle Cape, but no dominant along shore movement of sand north or 
south. From North Cape to Cape Romano are few stretches of beach, 
mangroves grow out of the water of the Gulf, the shore line is ex¬ 
tremely intricate. Tidal scour is strong at the inlets leading into White 
Water Bay, but to the north most of the entrances are obstructed by 
bars. From Cape Romano to the mouth of Caloosahatchee River the 
shore line topography approaches that of the east coast. Long beaches 
of sand, spits, bay bars denote adolescence. The predominant move¬ 
ment of sand along shore, as shown by offsets and overlaps, is south- 
