The formation of the island is madrepore, resting upon a core or base of stratified sand-stone grit, disposed in beds varying from 1·5 to 3 feet thick. The surface gently inclines towards the sea, and the lines of fracture run parallel with the shores. Three distinct formations occur to one crossing the breadth.[[35]] The first is a band of grit-based coralline, which runs meridionally, and is most remarkable on the eastern side. This portion, featureless and thinly inhabited, is protected from the dangerous swell and the fury of the Indian Ocean by a broad reef and scattered rocks of polypidoms. The band thins out to the north and south: in the centre, where it is widest, the breadth may be three to four miles, and the greatest height 400 feet. The coral-rag is mostly white and of many shapes, like fans, plants, and trees: the most usual form is the mushroom, with a broad domed head rising from a narrow stem. The texture is exceedingly reticulated and elastic; solid masses, however, occur where neighbouring rocks meet and bind—hence the labyrinth of caverns, raised by secular upgrowth and preserving the original formation. The ground echoes, as in volcanic countries, hollow and vault-like to the tread; the tunnels are frequently without issue for drainage, and when the rain drips in, the usual calcareous phenomena, stalactites and stalagmites, appear. Many of these caves are found on the coast as well as on the island. The carbonate of lime is very pure, and contains brown or yellow-white crystals.
A stony valley, sunk below the level of both flanks, is said to bisect the island from north to south. Into this basin fall sundry small streams, the Mohayra and others, which are lost through the crevices and caverns, and in the cracks and fissures of the grit. There are other drains, forming, after heavy downfalls, swamps and marshes, whence partly the great insalubrity of the interior. The western part of Zanzibar, with its wealth of evergreen vegetation, appears by far the most fertile. It is a meridional band of red clay and sandy hills, running parallel with the corallines of the eastern coast. Here are the most elevated grounds. I found the royal plantation Sebbé or Izimbane, 400 feet (B.P.) above sea-level, or a little higher than the Bermudas. The least productive parts are those covered with dark clay. Heavy rains deposit arenaceous matter upon the surface, and the black humus disappears. On this side of the island also many streamlets discharge into the sea, bearing at their mouths mangrove beds, whose miasmas cause agues, dysenteries, diarrhœas, and deadly fevers.
The rule established by Dampier and quoted by Humboldt directs us to expect great depth near a coast formed by high perpendicular mountains. Here, as in the rest of the Zanzibarian archipelago, the maritime line, unlike the west Atlantic islands Tenerife and Madeira, is composed of gently rolling hills. Yet seven fathoms are often found within a stone-throw of the land, whilst the encircling ledges are steep-to, marked in the charts 1/100 and 1/140. Evidently, then, the corallines are perched upon the summits of a submarine range which rises sharp and abrupt from abysmal hollows and depressions. As usual too in such formations, the leeward shore line of the island, where occur the lagoon entrances, is more varied and accidented than the eastern. At Pemba this feature will be even more remarkable.
The windward coast, in common with many parts of the continental seaboard, suffers especially from June to August from the Ras de Marée (Manuel de la Navigation et la Côte occidentale de l’Afrique), a tide race, supposed to result from the meeting of currents. It is a line of rollers neither far from nor very near the shore. The hurling and sagging surf is described to resemble the surge of a submarine earthquake; and the strongest craft, once entangled in the send, cannot escape. It would be useful to note, as at West African Lagos, the greater or less atmospheric pressure accompanying the phenomenon, and to seek a connection between it and the paroxysms of the neighbouring cyclone region. At all times sailors remark the ‘shortness’ of the waves and the scanty intervals between their succession. This peculiarity cannot be explained in the usual way by shoals and shallow water causing a ground-swell.
With respect to the great East African ocean-current, which has given rise to so many fables gravely recorded by the Arab geographers,[[36]] the best authorities at Zanzibar are convinced, and their log-books prove, that both its set and drift, like the Brazilian coast-stream, are in the present state of our knowledge subject to the extremes of variation. The charts and Horsburgh lay it down as a regular S.W. current; and so it is in the southern, whilst in the northern part it is hardly perceptible. Between Capes Guardafui and Delgado it flows now up then down the coast; here it trends inland, there it sets out to sea. Dr Ruschenberger relates that on Sept. 1, 1835, his ship, when south of Zanzibar, was carried 50 miles in 15 hours, and was obliged to double the northern cape. The same happened to Captain Guillain in August 1846, when he lost five days. This resulted from the superior force of the S.W. monsoon, which often drives vessels to the north 30 to 40 miles during the day and night. Lieut. Christopher (Journal, Jan. 5, 1843) reported it to be variable and violent, especially close in shore, and observed that it frequently trends against the wind. It is usually made to run to the S.W. between December and April, at the rate of 1·3 miles per hour, from Ra’as Hafun to Ra’as Aswad, and two to three miles per hour between Capes Aswad and Delgado. Shipmasters at Zanzibar have assured me that when this coastal current covers three knots an hour there is a strong backwater or counter-flow, which, like the Gulf-stream, trends to the north, and against which, with light winds, native vessels cannot make way. This counter-current has extensive limits; usually it is considered strongest between Mafiyah and Pomba. The ship St Abbs, concerning which so much has been said and written of late years, was wrecked in 1855 off St Juan de Nova of the Comoro group (S. lat. 17° 3′ 5″), and pieces of it were swept up to Brava (N. lat. 1° 6′ 8″), upwards of 1000 miles. The crew is supposed still to be in captivity amongst the Abghal tribe; and in 1865 an Arab merchant brought to Zanzibar a hide marked with letters which resembled N F B N. A writer in the Pall Mall opined the letters to be ‘Wasm’ or tribal brands, justly observing that ‘all the Bedawin have these distinguishing marks,’ but forgetting that he was speaking of the analphabetic Somal, to whom such knowledge does not extend. As we might expect, the Mozambique stream, south of Cape Delgado, always flows southerly with more or less westing. The rate is said to vary from 20 to 80 miles a day.
Our hydrographical charts are correct enough to guide safely into and out of port any shipmaster who will sound, and can take an angle. As, however, the navigation is easy, so accidents are common. Any land-lubber could steer a ship from Bombay to Karachi (Kurrachee), and yet how many have been lost! Often, too, it is in seamanship as in horsemanship, when the best receive the most and the heaviest falls. In May 1857 the Jonas, belonging to Messrs Vidal, was sunk by mistaking Chumbi Island for its neighbour Bawi. Three or four days afterwards the Storm King of Salem, Messrs Bertram, ran aground whilst hugging Chumbi in order to distance a rival. The number of reefs and shoals render it always unadvisable to enter the port at night, and in the heaviest weather safe riding-ground is found between Zanzibar Island and the continent.
ZANZIBAR FROM THE SEA.
Vessels from the south making Zanzibar in the N.E. monsoon, the trade-wind of December to March, leave Europa Island to the west, and the Comoro group and S. Juan de Nova on the east. Keeping well in mid-channel, they head straight for Mafiyah. They hug Point Puna, avoiding Latham’s Bank,[[37]] and they work up by Kwale and the Chumbi Island. Ships from the north have only to run down the mid-channel, between Pemba and the continent, and then to pass west of Tumbatu. Those sailing southward from Zanzibar at this season pass along-shore, down the Mozambique Channel. Vessels from the south making Zanzibar in May to September, the height of the S.W. monsoon—the anti-N.E. trade—sail up the same passage. They must beware of falling to leeward; and those that neglect ‘lead and look-out’ are ever liable to be carried northwards to Pemba by the counter-current before mentioned, which may, however, now be a wind-current. At this season ship-masters missing the mark have sometimes made 3° to 4° of easting, and have preferred beating down to Mafiyah and running up again, rather than face the ridicule of appearing viâ the northern passage. Those leaving the Island in the S.W. monsoon stand north up channel, well out in E. lon. 9° 42′ to 43′, beat south of Cape Delgado, pass between the Comoro group and the mainland, and thus catch the Mozambique gulfstream. The brises solaires blow strongest off Madagascar in June and July. They fall light in August and September.
The aspect of Zanzibar from the sea is that of coralline islands generally—a graceful, wavy outline of softly rounded ground, and a surface of ochre-coloured soil, thickly clothed with foliage alternating between the liveliest leek-green and the sombrest laurel, the only variety that vegetation knows in this land of eternal verdure. Everywhere the scenery is similar; each mile of it is a copy of its neighbour; and the want of variety, of irregularity, of excitement, so to speak, soon makes itself felt. Zanzibar ignores the exhilaration of pure desert air, and the exaltation produced by the stern aspect of mountain regions or by a boundless expanse of Pampa and Sahara. Without a single element of sublimity, soft and smiling, its sensuous and sequestered scenery has no power to spur the thought, to breed an idea within the brain. The oppressive luxuriance of its growth combined with the excess of damp heat, and possibly the abnormal proportion of ozone, are the most unfavourable conditions for the masculine. The same is the case in Mazanderan, Malabar, Egypt, Phœnicia, California, and other Phre-kah—lands of the sun. And the aspect of that everlasting, beginning-less, endless verdure tends, as on the sea-board of the Brazil, to produce sensations of melancholy and depression. We learn at last to loathe thee,