226 
FLORIDA STATE GEOLOGICAL SURVEY. 
of Hobe Sound suggest that the coquina there has acquired at least 
part of its hardness above sea level. One of the facts testifying to such 
consolidation is the presence at the spouting rocks of numerous ver¬ 
tical tubelike streaks of crystalline calcite which end in minute stal¬ 
actites, indicating a downward movement of lime-charged water 
through passages between sand grains. 
Coquina has been quarried for road metal at several localities along 
the east coast. For this purpose it is not so satisfactory as the Miami 
oolite, the coquina is not so calcareous as the oolite, is loosely cemented, 
where quarried, and breaks up instead of packing solidly. 
SANDS. 
The widespread mantle of sand that is so striking a feature of the 
central part of the peninsula extends into southern Florida as far as 
Miami on the east coast and to south of Everglade on the west coast. 
The sand is composed of angular grains of quartz, varying consider¬ 
ably in size. At the surface the sands are white or gray, below the 
surface they are of yellow, orange and red hues. The color is caused 
by iron oxide and represents the result of sub-aerial decay, the oxide 
coming from small grains of iron-bearing minerals, scattered through 
the sand. There seems to be no sharp dividing line between the gray 
and the colored sands, the intensity of color increasing with depth. The 
decoloration of the surface sands is due to the action of plant roots, 
the decay of vegetable matter and to leaching by rain. 
In places there is yellow sand finer and apparently more decayed 
than the bulk of the gray sand and the sand of the dunes seems to be 
finer and more highly colored than that of the sand plains and flat lands, 
but there are so many gradations of size and hue that to separate the 
sands into gray and yellow seems a useless undertaking. 
Whence came the sand is an interesting problem. Undoubtedly 
much of it represents the southward invasion of the peninsula by ma¬ 
terial worked down the Atlantic and Gulf coasts by waves and currents, 
the remnant of the material worn by streams from land far to the 
north. Some of it no doubt is all that is left of sandy limestones or 
marls that had accumulated below water level, and after partial or 
complete consolidation were elevated and worked over or leached, the 
limy material going away in suspension or solution. Possibly some 
of the sand now lying on the ground in southern Florida has been 
cemented to rock and reduced to separate particles many times since 
the grains were worn from some quartz-bearing rock in the hills of 
Alabama, Georgia or the Carolinas. 
In journeying down the shores the sands have been moved by the 
wind, blown inland, and the contours of the dunes represent wind 
action, as do to a large extent those of the rolling sand plains. 
