22 EXPEDITION OF THE "ALBATKOSS," 1899-1900. 



and beyond, islands which are not connected with the extensive plateau 

 upon which the greater number of the Pauraotu Islands to the westward 

 of Hao rise. 



All the islands we have examined are, without exception, formed of 

 Tertiary coralliferous limestone, which has been elevated to a greater or less 

 extent above the level of the sea, and then planed down by atmospheric 

 agencies and submarine erosion, the greatest elevation being at Makatea 

 (about 230 feet), and at Niau, where the Tertiary coralliferous limestone 

 does not rise to a greater height than twenty feet. At Rangiroa it was fif- 

 teen to sixteen feet high. At other islands it coald be traced only as form- 

 ing the shore platform, from fifty to 250 feet wide, which forms the outer face 

 of the Paumotus and is so characteristic a feature of the atolls of the group. 

 In other parts the old ledge could be traced cropping up in the interior of 

 the outer land-rim, or in the open cuts connecting the lagoon with the outer 

 sea-face of the atolls. Everywhere the space between the outcroppings of 

 the old ledge, as I will call the Tertiary coralliferous limestone, was filled 

 with beach rock, or a pudding-stone, or with a breccia or conglomerate of 

 coralliferous material consisting in part of fragments of the old ledge, and 

 of fragments of recent corals and shells cemented together. 



The appearance of the old ledge and of the modern reef-rock is so strik- 

 ingly different that it is very simple to distinguish the two, even where only 

 comparatively small fragments are found. 



We did not find in the Paumotus, as in Fiji, all possible stages of denu- 

 dation and of submarine erosion between islands like Vatu Vara, Naiau, 

 Kambara, Fulanga, Ongea, Oneata, Ngele Levu, and Wailangilala, and 

 atolls with a mere ring of surf to indicate their existence. 



In the Paumotus nearly all the islands have been elevated to a very 

 moderate height and probably to about the same height, for the old ledge 

 forming the base of the modern structure is found exposed nearly every- 

 where at about low-water when it cannot be traced at a slightly greater 

 elevation. This would readily account for the uniform height of the islands 

 throughout the group. 



But there is another element which comes into play in this group, and 

 has an important part in shaping the ultiuiate condition of these atolls. At 



