MANGA REV A. 69 



panorama of Manga Keva (Pis. GG, G9-71), and get an impression of the 

 relations of its different parts far better than can be conveyed by the 

 chart, for the whole of the visible part of the archipelago is included in 

 a line drawn east and west, north of Maka-pu ; south of that line the 

 position of the southwestern reef can be traced only by the discoloration 

 of the waters. 



Manga Reva is an intermediate stage of erosion and denudation, between 

 a lagoon archipelago such as Truk, and a barrier reef island like Vanikoro 

 and other islands in the Society groups, such as Bora Bora,^ Huaheine, 

 Eaiatea, Eimeo, in which the surrounding platform has comparatively little 

 width and the barrier reef is close to the principal island and often becomes 

 part of its fringing reef. Manga Reva is open to the south and to the west, 

 Vanikoro to the east, while the volcanic islands of Truk are completely 

 surrounded by the outer encircling reef, as are the Society Islands just 

 mentioned, which have several wide passages into the lagoon through the 

 wide barrier reef. 



One is tempted to reconstruct the Gambler archipelago of former times, 

 and to imagine it with a great central volcano, with a deep crater of more 

 than 34 fathoms, of which Manga Reva and Au Kena are parts of the rim 

 which once were connected from the southeast point of Manga Reva to Au 

 Kena, and thence along the line of the outer islets to the northeast end of 

 the former island. On the west face it was tlanked by smaller craters ex- 

 tending to the western islets of the encircling reef, of which the bays of Taku, 

 Kirimiro, and Rumaru, and the bays of the west side of Tara-Vai are the 

 eastern ridges. There were probably also other secondary volcanoes, of 

 which Aka-Maru and the islets of tlie south part of tlie lagoon are the rem- 

 nants, the latter all being situated on the gentle slope of the southern part 

 of the Manga Reva plateau ; this may have been the southern slope of the 

 principal volcano of the group, on the face of which have grown up the 

 outer lines of the encircling reef and its islets. 



The existence of a large central volcano would readily explain the depth 

 of the lagoon in its different regions, as well as the great depth of the outer 

 face of Manga Reva, depths showing slopes which are however no steeper nor 

 more striking than the height and slopes of the southern part of Manga 

 Reva (Pis. 58-G2), or Tara-Vai (PI. 65), of Aka-Maru (PL 67, fig. 1% and of 

 Maka-pu (PI. 67, fig. ;.'), supposing them to be extended into tiie sea. 



^ See A. Agatsiz, The Coral Reef:) of ibe Tropical I'acific, Plates 210 and 2:j1. 



