580 THE REEF-BUILDING CORALS. 
Bone Islet, from the remarkably white appearance of its beaches, the white coral fragments 
thrown up by the sea, appeared like bleached bones to the first visitors, hence Bone Cay, now 
Key West. 
It was the opinion of Professor Louis Agassiz that the entire peninsula of Florida had 
been built up from the sea-bottom by the several reef-building corals now living in the sur- 
rounding waters. This theory was seemingly verified by the discovery, in the interior of the 
state, of parallel ridges, which extend across the peninsula, and are the dead remains of species 
of corals that are seen living in the vicinity. 
The process of reef-building is easily comprehended by observing the present living forms, 
their growth and decay. We will observe a single egg of a reef-building coral, an astrea. 
As it floats in the deep sea, its ultimate destination as a single object is to rest on some solid 
base, and there develop into a simple polyp, in its first stages resembling an actinia or sea- 
anemone. We have observed the development of these eggs in a glass of sea-water, and we 
may assume that on the sea-bottom the little animal flower is passing through the same phases 
of development. Soon we notice at the base of the polyp the first layers of a foundation wall. 
When finished the creature represents the perfect coral animal. It is like a sea-anemone 
inclosed within a tube of lime. In some respects it is like a clam or other shell-fish in its 
shell, a perfect animal. It has several ways of growth and extension into family groups, by 
egos, and by development of buds out of its sides. If we take a piece of one of these reef- 
building corals in hand, we see that there are numerous stars, if it is an astrea, each star 
representing a single polyp, each a single animal ; but the hard parts, that serve as skeletons, 
or that correspond somewhat to the shells of clams and other shell-fish, are closely united. 
Practically the young members of the family, the buds, stay at home, and build on to the old 
home the first house, and the result is an indefinite number of tenements united in one block. 
The great ledges of astrean corals seen in the waters of the Florida Reef, are thus built up. 
This is the principal element in the foundation of a coral island. We may now regard the 
sea-bottom covered to a certain extent with the outspreading ledge of these united stars. 
Among the numerous elements that must be recognized in reef-building are various species ot 
burrowing shell-fish, and worms in great variety. These creatures kill the coral animals, and 
penetrate their limestone houses. Here we have the first steps in the building of the reef. 
The coral stars have secreted and deposited on the ocean bottom the masses of lime which 
form their houses; their enemies have destroyed them and penetrated their walls. The 
general débris of the ocean covers the broken walls. But the young of the coral animals are 
swimming in great numbers, ready to fasten upon any point. Myriads settle upon the old 
and dead ones, and found new houses; new blocks are built upon the old, and in time also 
yield to the inroads of their numerous enemies. The conflict thus goes on. The coral block 
of houses, solid material, becomes a compact mass, which rises gradually through this process 
of growth and decay, life and death, until this growing land has reached near the surface of 
the sea. In the shoaler water that now covers this coral-made land numerous small corals and 
algee grow, objects that require shallow water in which to thrive. Here is manifested a 
wise provision. The larger corals cease to thrive because the water is not sufficient, then 
smaller species appear, which, with the soft corals, as gorgonias, sea-feathers, and fans, and 
masses of corallines, the latter being algee or sea-weeds with solid lime bases, eventually 
quite bring the newly-made land to a point at the surface of the sea. Here we have an island, 
built up from the sea-bottom through the agency of living corals, their dead skeletons, alge, 
and the accumulated débris of ocean. This island would be of little service were it to 
remain at the ocean level. Nature has provided for the extension of this land. The man- 
grove tree is found growing on the extreme ocean border. Its fruit drops into the sea. This 
fruit is so much in shape, size, and color like a cigar, one is quite sure to be deceived on 
viewing it. Myriads of this fruit float over the new-made land; one end being heavier 
inclines to touch bottom. During the still water, after the summer solstice, these fruits 
throw out roots, which find their way rapidly and strongly into the earth. Soon they 
have put out leaves and have become trees. The roots, instead of disappearing beneath 
the soil, remain to a certain extent exposed, so that when the tree has gotten to be a 
