These curious and most useful splits of the land have been made since the maritime plain was complete, as we saw was the case with Dongonab Bay, and, consequently, part at least of the barrier system. In some cases the innermost parts of the harbours are composed of gravel, not elevated coral. At Fîjab this is due to erosion of the coral, as shewn by rocks and islets of this material remaining on the shallows which separate the gravel cliffs from the deeper water, but in other cases the gravel bounds the actual fault. This is well seen at Shinab, where almost the whole harbour is bounded by raised coral cliffs, but near the innermost end this is overlaid with gravel, and finally gravel replaces the coral in the most regular manner, shewing that the two materials were in perfect continuity when the split which made the harbour occurred. The north and south limbs of the crosses have been largely filled in with water and wind-carried sand; they were originally of much greater length. The peculiarities of the coast impress unusual methods upon those who travel along it by sea. The wave motion varies greatly; from Port Sudan to Darûr for instance the waves are much the same as on an open sea, from Darûr to Fîjab the barrier system gives considerable shelter, the vessel passing into perfect calm for short periods as she approaches near the reefs in tacking. From Shalak to the Têlat Islands is a bad bit in stormy weather, quite open sea and no possibility of anchoring anywhere in an emergency, so that vessels are often windbound at Salak[74] anchorage, waiting a fall in the wind in which to reach the next section of the barrier system. To travel by night is obviously impossible, the navigation of a boat, even among well-known reefs, when moonlight seems bright as day, is an experience once tried never repeated, without urgent cause. Even when the sun is low it is extremely difficult to see one’s way, though a good native pilot sees indications of reefs where all is a white glare to even an experienced Englishman. Consequently it is the invariable custom to get into the nearest harbour about four o’clock in the afternoon, and if the coast were not thus liberally provided, the natives’ travel by sea would be nearly impossible. The start is early next morning, between 2 a.m. and 4 a.m. according to the wind and the distance of the reefs. If the wind is fairly off shore, so that the neighbourhood of reefs will not be reached for some time, the start is early and the sail is hoisted in a strange silence, the sleepy sailors, on these occasions only, omitting their shouts and chants, and the vessel slips out of harbour like a slowly-gliding ghost.