The passage between them is practicable by small craft only, whose planks are sewed together, and are not affected by a stroke upon hard ground; for it is not for want of water that this navigation is dangerous. All the west coast is very bold, and has more depth of water than the east; but on this side there is no anchoring ground, nor shoals. It is a rocky shore, and there is depth of water every where, yet that part is full of sunken rocks; which, though not visible, are near enough the surface to take up a large ship, whose destruction thereupon becomes inevitable. This I presume arises from one cause. The mountains on the side of Egypt and Abyssinia are all (as we have stated) hard stone, Porphyry, Granite, Alabaster, Basaltes, and many sorts of Marble. These are all therefore fixed, and even to the northward of lat. 16°, where there is no rain, very small quantities of dust or sand can ever be blown from them into the sea. On the opposite, or Arabian side, the sea-coast of the Hejaz, and that of the Tehama, are all moving sands; and the dry winter-monsoon from the south-east blows a large quantity from the deserts, which is lodged among the rocks on the Arabian side of the Gulf, and confined there by the north-east or summer-monsoon, which is in a contrary direction, and hinders them from coming over, or circulating towards the Egyptian side. From this it happens, that the west, or Abyssinian side, is full of deep water, interspersed with sunken rocks, unmasked, or uncovered with sand, with which they would otherwise become islands. These are naked and bare all round, and sharp like points of spears; while on the east-side there are rocks, indeed, as in the other, but being between the south-east monsoon, which drives the sand into its coast, and the north-west monsoon which repels it, and keeps it in there, every rock on the Arabian shore becomes an _Iland_, and every two or three islands become a harbour. Upon the ends of the principal of these harbours large heaps of stones have been piled up, to serve as signals, or marks, how to enter; and it is in these that the large vessels from Cairo to Jidda, equal in size to our 74 gun ships, (but from the cisterns of mason-work built within for holding water, I suppose double their weight) after navigating their portion of the channel in the day, come safely and quietly to, at four o’clock in the afternoon, and in these little harbours pass the night, to sail into the channel again, next morning at sun-rise.