276 
APPENDIX. 
islets, seldom exceeding lialf a mile in breadth, which sur- 
mount the annular reefs of almost all the atolls in the 
Indian and Pacific Oceans. Moreover, there are evident 
proofs (Nelson, ibid. p. 118) that islands similar to the ex- 
isting ones formerly extended over other parts of the reef. 
It would, I believe, be difficult to find a true atoll with 
land exceeding 30 feet in height ; whereas, Mr. Nelson es- 
timates the highest point of the Bermuda Islands at 260 
feet; if, however, Mr. Nelson’s view, that the whole land 
consists of sand drifted by the winds and agglutinated to- 
gether, is correct, this difference would be immaterial ; but, 
from his own account (p. 118), there occur in one place 
five or six layers of red earth, interstratified with the ordi- 
nary calcareous rock, and including stones too heavy for 
the wind to have moved, without having at the same time 
utterly dispel sed every grain of the accompanying drifted 
matter. Mr. Nelson attributes the origin of these several 
layers, with their embedded stones, to violent catastrophes; 
but further investigation has generally succeeded in ex- 
plaining such phenomena by simpler means. Finally, I 
may remark that these islands bear a considerable resem- 
blance in shape to Barbuda in the West Indies, and to 
Pemba on the eastern coast of Africa, which latter island 
is about 200 feet in height, and consists of coral-rock. 
I believe that the Bermuda Islands, from being fringed by 
living reefs, ought to have been coloured red ; but I have 
left them uncoloured, on account of their general resem- 
blance in external form to a lagoon-island or atoll. Pro- 
fessor Dana (Corals and Coral Islands, pp. 218, 269) ranks 
them in this class. 1 
1 [The following particulars relating to Bermuda, taken from the 
Report of the Challenger Voyage, Na^ative, p. 138, are of interest: — 
An excavation made to form a bed for the floating dock went 
down to 50 feet below low-water mark. It cut through calcareous 
mud, loose beds (coral-sands mixed with mollusks, smaller corals 
and other organisms), passing into a loosely coherent freestone 
