Have built a series of nearly flat marine terraces abutting against one another much like a series of broad stairsteps. Erosion and solution have deface and, in places, have obliterated the original surficial forms of these old sea bottoms, shores, and shoreline feathers, but their remnants today are widespread and, in some places, are easily recognizable. Ice-age terraces higher than 100 feet above present sea level are not present in southeastern Florida. The flow in these streams is maintained largely by ground-water seepage from the aquifers underlying the higher terrace lands. Intermingling channels and honeycomb-like holes in the underlying rocks cause extremely high permeabilities in some of the limestone aquifers and produce conditions favorable for the development of well with exceptionally high yields and extremely low drawdowns.
Ground water occurs under both artesian and nonartesian conditions in southeastern Florida.
The Biscayne aquifer is composed mainly of sandy limestone and calcareous sandstone with beds and pockets of quartz. The aquifer is riddled with solution holes and generally filled with the sand, but numerous cavities of considerable size and extent occur. It is one of the most permeable aquifers ever investigated by the U.S. Geological Survey, and ranks with clean, well-sorted gravel in its capacity to transmit water. In the Fort Lauderdale well-field area the transmissibility is about 1,200,000 gpd per ft, but nearer the coast it is probably higher. The principle artesian aquifer of Florida is here named the Floridan aquifer.