PRELI5IINARY REPORT. 29 



pteropod ooze, and a few Globigerinae. Between Namuka and Yangasa 

 we obtained 324 fathoms; between Namuka and Marambo, 600 fathoms; 

 between it and Kambara, 450 fathoms ; and finally, about fifteen miles 

 west of Kambara, we sounded in 990 fathoms. These soundings would 

 indicate a continuous plateau of moderate depths from Wailangilala soutli, 

 upon which the islands of the Lau Group rise. 



On our way back to Papeete from the Paumotus we examined the east- 

 ern cost of Tahiti, and from Papeete examined the western coast as far as 

 Port Phaeton, at Taravoa Isthmus. We examined, in a general way, the 

 Leeward Society Islands: Murea, Huaheine, Raiatea, Tahaa, Bora-Bora, 

 Motu Iti, and Maupiti. There are excellent charts of the Society Islands, 

 so that it was comparatively simple to examine the typical points of the 

 group and to gain an idea of their structure as far as it relates to coral reefs. 

 The Society Islands are all volcanic islands edged witli shore platforms, 

 some of great width, upon which the barrier or the fringing reefs of the 

 islands have grown. The structure of the reefs of the Society Islands is 

 very similar to that of the Fiji reefs round volcanic islands. A comparison, 

 for instance, of the charts of Kandavu, Viti Levii, Mbengha, Nairai, and of 

 other volcanic i.slands in the Fijis, with those of the Society Group, will at 

 once show the identity of their structure. Huge platforms of submarine 

 denudation and erosion characterize both, with fringing and barrier reefs 

 determined by local conditions. Perhaps it is easier to follow the changes 

 which have taken place in the Society Islands ; and such islands as Tahaa 

 and Bora-Bora, where we anchored, as well as Maupiti, are admirable 

 examples and epitomes of the structure and mode of formation of the coral 

 reefs of that group. 



In Motu Iti and Tetiaroa the volcanic peaks have disappeared, leaving 

 nothing but a shallow platform, upon the outer edges of which sandy coral 

 i.slets have been thrown up. There is, however, one point in which the 

 barrier reefs of the Society Islands differ from those of Fiji. The barrier 

 reefs in Fiji are generally indicated merely by reef flats, upon which the sea 

 breaks, and an occasional rocky islet or negro-head ; only rarely do we find 

 sand keys upon the fringing reefs of the islands of Fiji. In the Society 

 Islands, on the contrary, we find the line of the barrier reefs usually well 



