EAST COAST OF AFRICA. 
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depth not being common, and about 12 feet the average. 
Outside the chain of islets, the sea, at the distance of a 
mile, varies in depth from 8 to 15 fathoms. Lieut. Boteler 
(Nar. vol. i. p. 369) describes the muddy bay of Patta, 
which seems to resemble other parts of the coast, as fronted 
by small, narrow, level islets formed of decomposing coral, 
the margin of which is seldom of greater height than 12 
feet, overhanging the rocky surface from which the islets 
rise. Knowing that the islets are formed of coral, it is 
I think scarcely possible to view the coast, and not at once 
conclude that we here see a fr ingin g-reef, which has been 
upraised a few feet : the unusual depth of from two to four 
fathoms within some of these islets, is probably due to the 
mud of the rivers having prevented the growth of coral 
near the shore. As several parts of this line of coast are 
undoubtedly fringed by living reefs, I have coloured it 
red . — Maleenda (3° 20' S.) : in the plan of the harbour, 
the south headland appears fringed ; and in Owen’s chart 
on a larger scale, the reefs are seen to extend nearly 30 
miles southward ; coloured red. Mornbas (4° 5' S.) : the 
island which forms the harbour ‘ is surrounded by cliffs of 
madrepore, capable of being rendered almost impregnable ’ 
(Owen’s Nar. vol. i. p. 412). The shore of the mainland, 
N. and S. of Mornbas, is regularly fringed by a coral-reef 
at a distance from half a mile to a mile and a quarter from 
the land ; within the reef the depth is from 9 to 15 feet ; 
outside the reef the depth at rather less than half a mile 
is 30 fathoms. From the charts it appears that a space 
about 36 miles in length, is here fringed ; coloured red. — 
Pemba (5° S.) is an island of coral formation, level, and 
about 200 feet in height (Owen’s Nar. vol. i. p. 425) ; it is 
35 miles long, and is separated from the mainland by a 
deep sea. The outer coast is represented in the charts as 
regularly fringed ; coloured red. The mainland in front of 
Pemba is likewise fringed . — Zanzibar resembles Pemba in 
