GEOGRAPHY OF CENTRAL FLORIDA 179

poses; and it is hard to draw the line between this and some of the low hammocks already mentioned.
 Salt marsh ituck. Along both coasts, in places protected from wave action by outlying or projecting land masses or the shallowness of the ocean bottom, are strips or patches of salt or brackish marsh, characterized by coarse grasses and rushes. The soil, a fine silt or muck, would probably be. quite fertile if it could be raised a few feet above sea-level, but being saturated with salt water twice a day (or all the time in tideless lagoons), little can be done with it. And the marshes of central Florida are doubtless less fertile than those near the mouths of muddy rivers farther north, as shown by the prevalence of the evergreen rush, Juncus Roemerianus, rather than the marsh grass, Spartina glabra, which has larger leaves and renews them every year.

 MISCELLANEOUS SOILS 
 Beach and dune sands. On the exposed portions of both coasts, except the greater part of that bordering the. Gulf hammock region, the sand has been piled by waves'and wind into beaches and low dunes, which are always more or less calcareous, owing to the presence of fragments of sea shells. The sand is usually rather fine, but contains very little silt or clay. Besides numerous mollusks, crustaceans, etc., that live before high tide level, a few gophers and ants make their homes in the beach sand, but salamanders are absent. The available chemical analyses (0, P, Z) seem to indicate that this soil is fairly well supplied with potash and other ingredients of fertility, but it is practically worthless for agriculture, on account of its instability, porosity, and lack of organic matter.
 Shell mounds. As already indicated under the head of topography, these are fomid in many places along the coast and navigable rivers. They consist mostly of shells of oysters and other bivalves, one kind of shell usually outnumbering all the rest in any one mound. The shells are usually little broken, and therefore contribute little to the soil, which is usually a thin layer of humus, with no sand or clay visible, though some of the mounds have considerable sand mixed with the shells. The vegetation seems to be always hammock of some kind, and on the east coast is usually decidedly tropical in composition, south of Cape Canaveral at least.
 Limestone cliffs and caves. Outcrops of tolerably pure and