SECOND ANNUAL REPORT—SOUTHERN EEORIDA. 
229 
sages about the keys; tidal and wind-made currents have heaped them 
up into flats and banks, and through the growth of vegetation they 
have become islands-. Such is the history of the gray marls on which 
flourish the mangrove forests of the Shark River archipelago and 
the Ten Thousand Islands. 
SANDS. 
The sands classified as recent are those of the shores, those that 
winds and waves move or bury in the work of destruction or construc¬ 
tion. At Jupiter Inlet and Palm Beach, Hillsboro Inlet and even as 
far south as Cape Florida the beach material is quartz sand with a 
varying proportion of ground-up seashells and other calcareous mate¬ 
rial. From Soldier Key around nearly to Cape Romano the beaches as 
a rule are of calcareous sand. Quartz grains, however, occasionally 
appear as far south as the keys, and of a series of forty-seven samples 
from the bottom of the inside passages collected between Biscayne Bay 
and Bahia Honda by Dr. Vaughan and examined by Mr. Matson, nearly 
all show quartz grains, though the grains are fine and not particularly 
abundant west of Card Sound. 
Along the shores of the keys from Soldier Key to Key West the 
beach sand consists of worn bits of corals, coraline algae and molluscan 
shells, with valves of pelecypods and whole shells of gastropods, and 
in many places, as at the sand pits on lower Metacumbe and Long Key, 
numerous branches of buckhorn coral (Pontes). The thicker deposits 
of this sand, five to eight feet at Lower Metacumbe, show the material 
to be roughly stratified with inconspicuous cross-bedding; the material 
includes occasional fragments of rock a foot long and has neither the 
texture nor the arrangement of a purely aeolian deposit. The beach 
ridges near the west end of Long Key, 5 feet above mean tide, show 
that they have reached their present height during hurricanes. The 
work of relatively high waves is particularly evident in the outlines of 
the beach ridges on one of the inner keys—Sand Key, off East Cape, 
exposed to seas entering the Bay of Florida from the Gulf. 
A striking peculiarity of these calcareous sands is their slight move¬ 
ment by the wind after the waves have heaped them up. Nowhere 
along the keys has the writer seen the sands moving before the wind, 
like the siliceous sands on the ocean shore at Palm Beach. As Hunt 1 
observed, the calcareous sands, once packed “resist the blasts of hur- 
icanes and northers.” 
CORAE REEFS. 
Along the arc of the keys from Soldier Key to the Tortugas, from 
four to seven miles off shore, are growing corals that form the Florida 
1 Hunt, E. B. Origin, Growth, Substructure, and Chronology of the Florida 
Reef, Amer. Jour. Sci. (2) XXV, 1863, p. 197. 
