256 
APPENDIX. 
most respects ; its southern half on the western side and 
the neighbouring islets are fringed ; coloured red . 1 On the 
1 [The following interesting account of Zanzibar is contained 
in a letter from Captain Wharton, found among Mr. Darwin’s 
papers : — 
‘ Zanzibar seems to me to have undergone several motions of sub- 
sidence and upheaval, the latter being the latest ; it appears now to 
have been for many years nearly stationary. 
‘ The island at present is surrounded with a nearly perfectly flat, 
dead, altered coral ledge, more or less dry at low water, without doubt 
the result of long action of the sea on the upheaved ancient and com- 
pressed coral of which the island is principally formed. This action 
has worn away the sea face of the land to the level of low water for a 
distance, in some instances, of 1| miles inside the original high-water 
line, which now remains as a steep rim, dropping to 10 and 20 fathoms 
almost immediately, with (on the outside of the island) 100 fathoms 
within a quarter of a mile. I could see no sign of this ledge extend- 
ing seaward, though there is living coral on its steep face visible a 
few feet below at low water, but this is not abundant, as it is on some 
of the detached reefs off the island. 
‘ The present high-water line of the island at the back of this flat 
area is, for the major part of its perimeter, a cliff of the same old 
coral from 10 to 20 feet in height, undermined by the waves, and 
overhanging, in some places, to a marvellous extent, showing the 
hardness and cohesion of the material, and giving a notion of the 
long period of time necessary to wear it away. As a further proof 
of this is the fact of very few lately detached pieces being seen at the 
foot of the cliffs, though the blocks, when they do fall, must be large 
and not easily moved by the sea. 
‘ In most parts of the island the tops of these low cliffs run back 
from the sea nearly level for a greater or less distance, showing water- 
worn coral wherever the surface rock is exposed, and indicating 
another stationary period or one of very slow upheaval. Out of this 
level the higher lands of the island rise. 
‘ Zanzibar is intersected by what may be regarded as 3 lines of hills 
running north and south, the highest of them being 450 feet above 
the sea. 
‘ I regret to add that I cannot say of what formation these hills 
may be ; I cannot call to mind any rock beyond the coral, which 
crops out at considerable heights (in one instance 250 feet), but there 
is a good deal of hardened clay or mudstone, which generally appears 
