1836.] SUBSIDENCE OF CORAL-REEFS. 475 
therefore, to affirm, that on the theory of the upward growth of 
the corals during the sinking of the land,* all the leading fea- 
tures in those wonderful structures, the lagoon-islands or atolls, 
which have so long excited the attention of voyagers, as well as 
in the no lesg,wonderful barrier-reefs, whether envircling~small 
islands or en ae for ugitet of miles: along the shores sia a 
continent, are Simply ¢ Nained. om 
It may be aked ae 1 can offer any direct evidence of 
the subsidence’of Fpdirids “reefs'or ‘atolls; but it must be borne in 
mind how difficult it‘ must ever bets detect ‘a movement, the 
tendency of which is to hide under water the part affected.: Ne- 
vertheless, at Keeling atoll I observed on all sides of the Jagoon 
old cocoa-nut trees undermined and falling; and in one place 
the foundation-posts of a shed, which the inhabitants asserted 
had stood seven years before just above high-water mark, bu 
now was daily washed by every tide: on inquiry I found that 
three earthquakes, one of them severe, had been felt here during 
the last ten years. At Vanikoro,' the lagoon-channel is remark- 
ably deep, scarcely any alluvial soil has accumulated at the foot 
of the lofty included mountains, and remarkably few islets have 
been formed by the heaping of fragments and sand on the wall- 
like barrier-reef; these facts, and some analogous ones, led me. 
to believe that this island must ‘lately have subsided and. the 
reef grown upwards: here again ‘earthquakes are frequent’ and 
very severe. In the Society archipelago, on the other hand, 
where the. lagoon-channels are almost' choked up, where much 
low alluvial Jand has accumulated, and‘where in some cases long 
islets have been formed on the barrier-réefs—-faets all showing 
that the islands have not very lately subsidéd—only feeble shocks 
are most rarely felt. In these coral formations, where the land 
and water seem struggling for mastery, it must be ever dificult 
to decide between the effects of a change in the set of the tides 
and of a slight subsidence: that many of these reefs and atolls 
* It has been highly satisfactory to me to find the following passage in a 
pamphlet by Mr. Couthouy, one of the naturalists in the great Antarctic Ex- 
pedition of the United States:— Having personally examined a large 
number of coral-islands, and resided eight months among the volcanic 
class having shore and partially encircling reefs, I may be permitted 
to state that my own observations have impressed a conviction of the cor- 
rectness of the theory of Mr. Darwin.”—The naturalists, however, of this 
expedition differ with me on some points respecting coral formations, 
