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separated into distinct portions ; and these portions wouldtend to assume an atoll-like structure, from the coral growingwith vigour round their entire circumferences, when freelyexposed to an open sea. As we have some large islandspartly submerged with barrier-reefs marking their formerlimits, such as New Caledonia , so our theory makes itprobable that there should be other large islands whollysubmerged; and these, we may now infer, would be sur-mounted, not by one enormous atoll, but by several largeelongated ones, like the atolls in the Maldiva group;and these again, during long periods of subsidence, wouldsometimes become dissevered into smaller atolls. I mayadd, that both in the Marshall and Caroline Archipel-agoes, there are atolls standing close together, which havean evident relationship in form : we may suppose, in suchcases, either that two or more encircled islands originallystood close together, and afforded bases for two or moreatolls, or that one atoll has been dissevered. From theposition, as well as form, of three atolls in the CarolineArchipelago (the Namourrek and Elato group), whichare placed in an irregular circle, I am strongly temptedto believe that they have originated by the process ofdisseverment . 1
Irregularly-formed atolls .—In the Marshall group, Mus-quillo atoll consists of two loops united in one point ; and
1 The same remark is, perhaps, applicable to the islands of Ollap,Fanadik, and Tamatam in the Caroline Archipelago, of which chartsare given in the atlas of Duperrey’s voyage : a line drawn through thelinear reefs and lagoons of these three islands forms a semicircle.Consult, also, the atlas of Lutke’s voyage; and for the Marshall groupthat of Kotzebue ; for the Gilbert group consult the atlas of Duperrey’svoyage. Most of the points here referred to may, however, be seenin Krusenstern ’s general Atlas of the Pacific.