AGASSIZ : FIJI ISLANDS AND COKAL liEEFS. 53 



case, I am inclined to consider these central basins as due to the action 

 of atmospheric agencies, and to look upon them as similar to the gigantic 

 banana holes, as they are called, occurring in the Bahamas, whicli are 

 undoubtedly due to the solvent action of tlie rains overcharged with car- 

 tonic acid, which carry off the limestones, and, percolating through the 

 mass, leave the saucer-shaped basins characteristic of the so called ele- 

 vated atolls. In such islands as Xaiau, Vanua Vatu, Tuvutha, Kambara, 

 and Wangava, the central depression has not extended very far towards 

 the sea level. But in such islands as Mango the central depression has 

 formed a small lagoon, in Namuka submarine erosion has carried off one 

 side of the rim ; in Fulanga (Plate 22) the process has been carried 

 still farther by the direct action of the sea and of submarine erosion, 

 forming a large lagoon ; and the conditions existing at Ongea, Yangasa, 

 Aiwa, and finally at Reid Haven, Wailangilala, iSTgele Levu, etc., illus- 

 trate the different stages in the transformation by submarine erosion of a 

 so called elevated atoll of tertiary age into an atoll of the present epoch. 

 The probable extent to which atmospheric agencies have conti-ibuted 

 to shape such central basins is also shown fi'om the presence of exten- 

 sive caves in the elevated limestone islands of Vatu Leile, of Thithia, 

 and of Ngillangillah, and in the numerous cracks, caverns, and cavities 

 which characterize the faces of the vertical bluffs of elevated limestone 

 wherever we have met them in the Fijis (see Plates 74, 77, 92). 



^VATU VARA, SEEN FROM THE EAST. 



Vatu Vara. 



Plate 19. 



On the last trip of the " Yaralla " from Suva to Wailangilala, Captain 

 Thomson examined for me the islands of Vatu Vara, Yathata, Kaimbo, 

 and Naitamba. The accompanying account is based upon his notes. 



