428, of the “Voyage of the _Astrolabe_,” and the large accompanying chart taken chiefly from that given by Duperrey) are high, and the rest are all small, low, and formed on the reef. The depth of the great interior lake has not been ascertained; but Captain D’Urville appears to have entertained no doubt about the possibility of taking in a frigate. The reef lies no less than fourteen miles distant from the northern coasts of the interior high islands, seven from their western sides, and twenty from the southern; the sea is deep outside. This island is a likeness on a grand scale to the Gambier group in the Low Archipelago. Of the groups of low[1] islands forming the chief part of the Caroline Archipelago, all those of larger size, have the true atoll-structure (as may be seen in the “Atlas” by Captain Lutké), and some even of the very small ones, as _ Macaskill_ and _Duperrey_, of which plans are given in the “Atlas of the _Coquille’s_ Voyage.” There are, however, some low small islands of coral-formation, namely _Ollap, Tamatam, Bigali, Satahoual_, which do not contain lagoons; but it is probable that lagoons originally existed, but have since filled up: Lutké (vol. ii, p. 304) seems to have thought that all the low islands, with only one exception, contained lagoons. From the sketches, and from the manner in which the margins of these islands are engraved in the “Atlas of the Voyage of the _Coquille_,” it might have been thought that they were not low; but by a comparison with the remarks of Lutké (vol. ii, p. 107, regarding Bigali) and of Freycinet (“Hydrog. Memoir _ L’Uranie_ Voyage,” p. 188, regarding Tamatam, Ollap, etc.), it will be seen that the artist must have represented the land incorrectly. The most southern island in the group, namely _ Piguiram_, is not coloured, because I have found no account of it. _Nougouor_, or _Monte Verdison_, which was not visited by Lutké, is described and figured by Mr. Bennett (_United Service Journal_, January 1832) as an atoll. All the above-mentioned islands have been coloured blue. [1] In D’Urville and Lottin’s chart, Peserare is written with capital letters; but this evidently is an error, for it is one of the low islets on the reef of Namonouyto (see Lutké’s charts)—a regular atoll.