ORIGIN OF BARRIER REEFS AND ATOLLS. 261 
DARWIN’S THEORY OF THE ORIGIN OF BARRIER REEFS 
AND ATOLLS. 
Mr. Darwin, in his voyage around the world as natu- 
ralist of the expedition of the “Beagle,” under Captain 
Fitzroy, R. N., during the years 1832 to 1836, visited and 
investigated the Keeling atoll in the Indian Ocean, and the 
barrier and fringing reefs of Tahiti. With the facts thus 
gathered, he had a key to all descriptions and maps of the 
reefs and reef islands of the oceans, and through careful 
study of the resources at hand, he arrived at a comprehen- 
sive knowledge of the facts and a theory of their origin.' 
The voyage of the author in 1858 to 1842 brought the sub- 
ject to his attention, and afforded him abundant illustrations 
of all sides of the subject and elucidations of some points 
which had been deemed obscure; and he believes that the 
collected facts place the theory on a firm basis of evidence. 
Darwin's theory is this: that a fringing reef skirting 
an ordinary island becomes changed by means of a slow 
subsidence and the compensating upward growth of the 
corals into a barrier reef; and that the barrier reef, by the 
continuation of the sinking until the old island has dis- 
appeared, and by the same process of growth, becomes finally 
an atoll. 
1 The third edition of Darwin’s work, issued in 1889, contains a valuable appen- 
dix by Prof. T. G. Bonney, giving a full review of the new contributions to the sub- 
ject of coral reefs, and his own views confirmatory of those of Darwin. 
® The author, besides working among the reefs of Tahiti, the Samoan (or Navi- 
gator) Islands, and the Feejees (at this last group staying three months), was also 
twice at the Hawaiian Islands. In addition, he landed on and gathered facts from 
fifteen coral islands, — seven of these in the Paumotu Archipelago; one, Tongatabu, 
in the Friendly Group; two, Taputeuea and Apia, in the Gilbert Group; and five 
others near the equator, east of the Gilbert Group, Swain’s, Fakaafo, Oatafu (Duke 
of York’s), Hull, and Enderbury’s Island. 
