372 Agassiz — Albatross Expedition to the Eastern Pacific. 



are seen to the northeast about 4 miles off. When on the sum- 

 mit of the central ridge of Manga Beva one can, in a radius of 

 a little more than 4 miles, take in the whole panorama of 

 Manga Beva, and get an impression of the relations of its 

 different part 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, south of Maka-pu ; south of that 

 line the position of the southwestern reef can be traced only 

 by the discoloration of the waters. 



Manga Beva is an intermediate stage of erosion and denuda- 

 tion, between a lagoon archipelago such as Truk, and a barrier 

 reef island like Yanikoro, and other islands in the Society 

 groups such as Bora Bora,* Huaheine, Baiatea, 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 Beva is open to the south 

 and to the west, Yanikoro to the east, while the volcanic islands 

 of Truk are completely surrounded by the outer encircling bar- 

 rier 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 G-ambier Archipelago of 

 former times and to imagine it with a great central volcano, 

 of which Manga Beva and Au Kena are parts of the rim 

 which once were connected from the southeast point of Manga 

 Beva to Au Kena, and thence along the line of the outer islets 

 to the northeast end of the former island with a deep crater of 

 more than 34 fathoms. On the west face it was flanked by 

 smaller craters extending to the western islets of the barrier 

 reef, of which the bays of Taku, Kirimiro and Bumaru, and 

 the bays of the west side of Tara Yai are the eastern ridges. 

 There were probably also other secondary volcanoes, of which 

 Aka Maru and the islets of the south part of the lagoon are 

 the remnants, the latter all being situated on the gentle slope 

 of the southern part of the Manga Beva 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 barrier 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 off the outer face of Manga Beva, 

 depths showing slopes which are no steeper nor more striking 

 than the height and slopes of the southern part of Manga Beva 

 or Tara Yai, of Aka Maru, and of Maka-pu, supposing them 

 to be extended into the sea. 



*See A. Agassiz, — The Coral Eeefs of the Tropical Pacific, Plates 210 and 

 231. 



