194 On Coral Reefs and Islands. 
~ these views. These points or capes correspond to points in the 
original land, and often to the line of the prominent ridge ; and 
it is well known that such ridge-lines often extend a long dis- 
nce with slight inclination compared with the slopes or de- 
Clivities bounding the ridge on either side. 
Coral islands or reefs often lie in chains like the peaks of a 
single mountain range:—for example, the sickle-shape line of 
islets north of Nanuku. Taritari and Makin, (Tarawan group, 
see map in vol. xii,) lie together as if belonging to parts of one 
island. Menchicoff atoll, in the Caroline Archipelago, consists 
of three long loops or lagoon islands, united by their extreml- 
ties, and further subsidence might reduce it to three islands.* 
The sizes of atolls offer no objection to these views, as they 
do not exceed those of many barrier reefs. Some of the larger 
Maldives, according to the crater theory, would require a crater 
seventy miles in diameter, with a rim’ made up of subordinate 
eraters. No hypothesis of such extravagance is necessary. ‘The 
facts all fall in with known principles, and are illustrated by known 
and established truths, without hypotheses of any kind. 
It is of some interest to follow still further the subsidence of a 
Pp 
gradually obliterated, and the large atoll is thus reduced to 4 
mulations in filling up the lagoon; and as filled lagoons are fou 
only in the smallest islands, such as Swains and Jarvis, the two 
agencies have beyond doubt been generally united. 
This subsidence, if more rapid than the increase of the coral 
reef, becomes fatal to the atoll, by gradually sinking it beneath 
the sea. Of this character evidently is the Chagos Bank.t The 
southern Maldives have deeper lagoons than the northern, fifty 
See Comet lagoons than the northerd, °F 
* See Darwin on the probable disseverment of the Maldives, op. cit., P- 37, » 
which he points out indications of a breaking up of a large atoll into several smaller. 
A land with many summits or es of heights may at ve its single enclos- 
ing reef; but as it subsides, this reef contracting upon itself may encircle separately 
the several ranges of which the island consisted, and thus several atoll reefs may 
result in place of the large one; and further, each may ly become the 
basis of a separate lagoon island, under a certain rate of subsidence or variations In 
it, provided the outer reef is so broken as to admit the influe waves and 
winds. The Maldives are a good example of this result. Some of the large atolls 
are ay atoll archipe : 
+ For a detailed account of this and other submerged reefs, see Darwin, p. 106- 
