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 forme, 

 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 

 eggs, 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 of 

 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 debris 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 

 algae 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 algae 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, algae, 

 and the accumulated debris 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 



