94 



SCIENCE. 



[N. S. Vol. XI. No. 264. 



the SOO-fathom line ; that such islands as 

 Anaa are probably on spurs or independent 

 smaller plateau, separated from the main 

 plateau by somewhat deeper water. The 

 same may be the condition of Earoia and 

 Takume and of Hao and Amanu, while 

 such smaller and isolated peaks as Tikei, 

 Aki-Aki, ISTukutavake, and Pinaki, as well 

 as the Gloucester Islands, rise from greater 

 depths and are isolated peaks. At any rate, 

 these soundings indicate, as do the sound- 

 ings off the Fijis, that atolls do not neces- 

 sarily rise from very great depths, and that 

 in this characteristic atoll district, atolls 

 are found, it is true, with steep slopes, but 

 rising from moderate depths. The slopes 

 of these atolls would probably resemble in 

 every respect the slope of the elevated 

 coralliferous limestone islands characteris- 

 tic of the Lau Group in Fiji. 



The deepest sounding among the Paumo- 

 tus was on the line to the northward of 

 Hereheretue in the direction of Mahetia, 

 where we found a depth of 2524 fathoms, 

 and a continuation of the red clay char- 

 acterizing the soundings since we left 

 Pinaki. In nearly all the soundings among 

 the Paumotus, even at moderate depths not 

 far from the atolls, we brought up man- 

 ganese particles or small manganese nod- 

 ules. The last haul, made in deep water on 

 the way from Hereheretue, in 2440 fathoms, 

 brought up at least half a ton of manganese 

 nodules, the bottom being red claj^. 



We have now steamed about 2.500 miles 

 among the Paumotus, and although we had 

 not the advantage of the accurate surveys 

 of the English hydrographic charts, which 

 made the exploration of Fiji so easy, yet 

 from the structure of these atolls it was a 

 comparatively simple task, by steaming 

 around the islands and landing wherever 

 practicable, to get a fairly good idea of their 

 structure. We have seen nothing in this 

 more extended examination of the group 

 tending to show that there has anywhere 



been subsidence. On the contrary, the con- 

 dition of the islands of the Paumotus can- 

 not, it seems to me, be explained on any 

 other theory except that they have been 

 formed in an area of elevation ; an area of 

 elevation extending from Matahiva on the 

 west to Pinaki in the east, and from the 

 Gloucester Islands on the south to Tikei in 

 the north, although the islands in the line 

 of Mangareva to Tahiti are separated from 

 the other Paumotus by a deep channel, 

 nearly 200 miles wide and more than 2400 

 fathoms in depth, with scattered islets and 

 atolls extending from Mangareva to Pinaki, 

 and northward to Serle Island 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 coral- 

 liferous limestone which has been elevated 

 to a greater or less extent above the level 

 of the sea, and then planed down by atmos- 

 pheric 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 20 feet. At Rairoa' it 

 was 15 to 16 feet high. At other islands it 

 could be traced only as forming the shore 

 platform, from 50 to 150 feet wide, which 

 forms the outer face of the Paumotus, and 

 is so characteristic a feature of the atolls 

 of the gi'oup. In other parts the old ledge 

 could be traced cropping up in the interior 

 of the outer rim, or in the open cuts con- 

 necting the lagoon with the outer sea face 

 oftheatolls. Everywhere the space between 

 the outcropping 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 coral- 

 liferous material consisting in part of frag- 

 ments of the old ledge and of fragments of 

 recent corals and shells cemented together. 



