Let it not be supposed we are here advancing a theory: we are only stating a fact that has been established by close and repeated observations. All the phenomena exhibited in the development of the Polypidom, are exhibited no less plainly in every Coral Reef that has yet been examined. On the surface of the Reef are the living Zoophytes, clinging to the calcareous skeleton which is ever growing larger through the unconscious action of their vital functions; while immediately beneath may be seen the same stony skeleton, already divested of its fleshy integument, and beginning to assume the appearance of compact and massive rock. We can behold, therefore, the mason at work on the upper story of his building, and the structure already finished below. And so we have little less than ocular demonstration that the Coral Reef is the work of the Zoophyte. It must not be supposed, however, that in every part of the Coral Reef, the form and outline of the stony skeleton are exactly preserved. Fragments of the rock are broken off by the force of the waves, and mixed up with the comminuted shells of oysters, mussels, and other crustaceous animals inhabiting the same waters. In this way a sort of calcareous gravel, sometimes a calcareous paste, is formed, which fills up the interstices, and connects the tree-like coral into a compact rock. We have yet to explain how the Coral Reefs come, in many cases, to rise above the surface of the ocean, and to form dry land: for it has been found that the reef-building Zoophytes require to be continually immersed in salt water, and therefore, by their own efforts, they cannot raise their structure above the ordinary level of the sea. This question was for a long time involved in obscurity; but it has been cleared up by the actual observations of Naturalists in modern times. The following description, which is given to us by Chamisso, the companion of Kotzebue on his voyages, will convey a good idea of the process by which a sunken reef is often converted into a smiling, fruitful island. “When the reef is of such a height that it remains almost dry at low water, the corals leave off building. Above this line a continuous mass of solid stone is seen, composed of the shells of mollusks and echini, with their broken-off prickles and fragments of coral, united by calcareous sand, produced by the pulverization of shells. The heat of the sun often penetrates the mass of stone when it is dry, so that it splits in many places, and the force of the waves is thereby enabled to separate and lift blocks of coral, frequently six feet long and three or four in thickness, and throw them upon the reef, by which means the ridge becomes at length so high that it is covered only during some seasons of the year by spring tides. After this the calcareous sand lies undisturbed, and offers to the seeds of trees and plants cast upon it by the waves, a soil upon which they rapidly grow, to overshadow its dazzling white surface.