On the Geology of the Florida Keys. 391 
quite hard, especially where it is exposed alternately to the action 
of the tides and atmosphere. This indurated crust may be seen 
on the road between the town and the barracks, and around the 
salt-works. Below this crust the rock is quite soft, and in some 
most striking difference, next to that of organic remains, consists 
in the distinctly oolite structure of the Florida limestone. This 
structure is seen where one would be led to expect it, in the 
fine-grained seams. A few hundred yards from the hospital a 
quarry has been opened where the rock may be examined. The 
organic remains consist of broken shells and water-worn frag- 
ments of corals, which, both in species and state of preservation, 
resemble those on the shores of the island. Except in degree 
of hardness, the rock does not differ from the calcareous sands 
thrown up by the waves on the shore in the vicinity ; and the 
conditions presented by the loose moving sands, are not favorable 
to the habits of molluscous animals, nor are fossil shells very 
abundant in the limestone of the island. Oblique or false strati- 
fication is everywhere seen in the rock, the inclination of the 
planes differing very little from the slope of the shore up which 
the waves push dead shells, pieces of coral, &c. After a breeze, 
coarse materials are found strewing the beach, a light wind leaves 
a finer deposit, and in the succeeding calm the sea appears milky 
from fine calcareous matter suspended in the water; this Is de- 
posited in the form of free impalpable mud which invests marine 
plants and other objects, to which it adheres with great tenacity, 
and becomes a source of annoyance to collectors of Alge. 
these alternations of fine and coarse materials may be observed 
in the limestone. 
Along the south beach, the sand is thrown up by the waves to 
an elevation nearly equal to that of the highest point of the 
a island, and during the gale of Oct. 1841, the greater part of it 
bs was submerged, so that, at first sight, it might appear that the 
whole island was the result of sand thrown up at such times. 
But although I observed no beds in the limestone that prove, like 
those of our tertiary, that the animals whose remains they con- — 
t shows the 
the coast, evidences of gradual elevatory movements. = 
On Key West I found in the rocks, no beds of corals retaining 
although large fragments are. scattered 
Living corals of two or three genera are 
t in the surrounding shallow water. i | 
ome of .the small Keys, such as the Mangrove Keys, are the 
of gradual deposition of sedimentary matter, many of those 
Spersed among the larger islands have not yet reached. the 
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