ABSTRACT
This chapter presents a very brief account of the three great classes of coral-reefs namely, Atolls, Barrier, and Fringing-reefs, and explains the author's views on their formation. As the barrier-reef slowly sinks down, the corals will go on vigorously growing upwards; but as the island sinks, the water will gain inch by inch on the shore-the separate mountains first forming separate islands within one great reef-and finally, the last and highest pinnacle disappearing. In these coral formations, where the land and water seem struggling for mastery, it must be ever difficult to decide between the effects of a change in the set of the tides and of a slight subsidence: that many of these reefs and atolls are subject to changes of some kind is certain; on some atolls the islets appear to have increased greatly within a late period; on others they have been partially or wholly washed away.
