496 Mr Crossland, The Coral Reefs of Zanzibar. 



sometimes almost black. Empty spaces or pockets of red earth 

 are often included in it. Fossil corals, shells and echinoderm 

 spines are abundant 1 , differing little from the remains of animals 

 living in the adjacent seas. Corals are found embedded in the 

 cliffs still in the position in which they grew. The surface is 

 always pitted and covered with sharp points and ridges like the 

 broken surface of a slag. Small caves are frequent along the coast, 

 and many rocks have most fantastic shapes. The cliffs of Ras 

 Juja in Chuaka Bay are cut to form an area covered by pinnacles 

 close together, whose tops reach the usual height of the cliffs, 

 and whose bases rise from a rock platform at low tide level. 

 Mangroves, which often grow on the rock in Chuaka Bay, stand 

 thickly among them. 



The sand and chalk formations lie usually above the coral, 

 forming most of the surface of the central plateau, and so far 

 as I have seen, all of that of the highest hills, which attain 

 a height of 440 feet. Hills composed mainly or entirely of coral 

 rock only occur in the north, south and east, the highest of which 

 is Kidoti Hill in the north-west, whose summit of coral rock is 

 250 feet above sea level. The extensive eastern plains are com- 

 posed almost entirely of coral rock, and are interrupted by only 

 a few isolated hills of the same from 70 to 200 feet in height. 



The sheltered west coast is a succession of islands, shoals 

 and long bays. The eastern, or ocean coast outline, would have 

 a regular contour line but for Mnemba Reef and Chuaka Bay. 

 The latter is five miles wide, and at low springs is mainly an 

 expanse of sand. The creeks at its head run inland for a con- 

 siderable distance along a depression which crosses the island to 

 Menai Bay on the south-west coast. 



Mnemba Reef is separated from Zanzibar by a channel, one 

 and a quarter miles wide, having an average depth of 40 

 fathoms, being thus more deeply separated than is Zanzibar 

 from the African mainland. The island of Mnemba, situated 

 on the south-west of the reef, is about a quarter of a mile long, 

 composed entirely of fine loose sand in which casuarinas and 

 pandani grow. 



The Reefs of the East Coast. 



The outer edge of the whole reef lies at a height of 2 feet 

 above the mean low tide level, being thus 3 feet above the 

 lowest springs. The distance of its highest part to the lowest 



1 In this abundance of fossils this rock differs from the otherwise very similar 

 raised coral rock described by Gardiner in the Lau group, Fiji, Proc. Camb. Phil. 

 Soc. vol. ix. Part vin. On Funafuti, Botuma, and Fiji, p. 457. 



