THE FLORIDA REEFS. 77 
here brought forward. Mr. Murray’s “ observations of the reefs 
at Tahiti! support the view that they have been built from the 
shore seawards, and that the lagoons have been and are still 
being formed by the removal of the inner and dead portions 
of the coral reef by the solvent action of sea-water. . . . The 
food supply for the masses of living coral on the ütey slope 
of the reef is brought by the oceanic currents sweeping past 
the islands, — а fact which explains the more vigorous growth 
of the reef on the windward sides. It is maintained by Mr. 
Murray that the whole of the phenomena of the Tahiti reefs 
may be fully explained by reference to the processes at present 
in action, and without calling in the aid of subsidence, as is 
done by Darwin and Dana ; and it is further argued that the 
form of atoll and barrier reefs generally can be: explained on 
the same principles." 
Undoubtedly, Darwin's theory of reef formation presents a 
sound and admirable exposition of the grander.causes which 
have brought about the elevation or subsidence of large tracts 
to a level favorable for coral growth ; but at the time he wrote 
upon this subject, the formation of extensive limestone banks, 
built up by the animals living on the bottom, and constantly 
strengthened and increased by the attendant phenomena of 
winds and currents, was little understood. These facts have 
been brought into notice and emphasized by recent deep-sea 
explorations. Darwin, however, when examining maps of the 
West Indies, had been struck by the probable connection be- 
tween the areas of deposition of the great banks marked upon 
the charts and the course of the sea-currents. He naturally ex- 
plained the steep slopes, abruptly dropping from comparatively 
shallow plateaux to great depths, by what is known to occur 
wherever great masses of sediment are found, and he therefore 
considered these plateaux to be submerged mountains. Such 
they are, in a certain sense ; not wholly built, however, as Dar- 
win supposes, of sediment, but in great part also of the remains 
of the innumerable animals living and dying upon them. The 
nucleus of these banks has probably béen formed around the 
shores of promontories subjected to the most active play of the 
great oceanic currents. 
1 Voyage of the “ Challenger,” Narrative of the Cruise, p. 781. 1885. 
