".–During the voyage of the and subsequently, Mr Darwin made a profound study of s, and has given a theory of their mode of formation which has since been universally accepted by scientific men. Darwin's theory may be said to rest on two facts—the one physiological, and the other physical—the former, that those species of corals whose skeletons chiefly make up reefs cannot live in depths greater than from 20 to 30 fathoms; the latter, that the surface of the earth is continually undergoing or ."