There are no stones of any size on the edges of the reefs, nothing but a few pieces of coral, a foot or so in diameter at most, project above lowest water level. It would decrease the danger of navigation in dead calm weather, which at present, except in frequented places, is considerable, if larger stones, such as the “negro-heads” of some reefs, were present at intervals. As in most cases these larger masses are the remains of former land and are not, as sometimes stated, fragments of the living reef thrown up by storms, one cannot expect their presence here, where the reef edge has grown up _in situ_. But even large boulders such as form the “hurricane beach” of Pacific atolls, and are cast up by storms in profusion on the reefs of Queensland, are not found here. There is plenty of strong wind in the Red Sea, but the strongest of all, the hot winds of summer, blow off land and do not extend far to sea and such vast breakers, up to 40 feet high, as are recorded of the Pacific, never occur. The reef edge above the precipice consists of a slope of stunted coral which above water-level changes to a gravel of coral fragments coated with lithothamnia; within is sand, generally with bands of seaweeds and marine flowering plants (grass-like in appearance) on the shallows, with muddy pools and channels a fathom or two deep. The edge is higher than the rest, but does not appear continuously above lowest water-level. Reefs not exposed to the waves have not this definite edge, the platform being covered with two or three feet of water in which stand separate coral colonies, numerous at the edge, rarer within towards the lagoon. The crescentic or circular forms of isolated reefs is very far from being a peculiarity of the Red Sea, but is worth while mentioning as bearing on the formation of the lagoons of atolls on the larger scale. From the smallest to the largest these reefs shew a hollowing out in the centre, where the reef material, not being protected by living matter, is exposed to the destructive influences detailed in Chapter VIII.