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 vm. On Funafuti, Rotuma, and Fiji, p. 457. 
