22 EXPEDITION OF THE “ALBATROSS,” 1899-1900. 
and beyond, islands which are not connected with.the extensive plateau 
upon which the greater number of the Paumotu 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 could 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 ultimate condition of these atolls. At 
