692 



SCIENCE. 



[N. S. Vol. XXI. Xo. 540. 



part of the lagoon are isolated fragments, 

 steep, greatly weathered and disintegrated. 

 No soundings exist to show their relation 

 to the other islands of the group. 



The soundings thus far made indicate in 

 the southern part of the lagoon a depth of 

 about 23 fathoms, with an occasional hole 

 of from 38 to 40, and a gradual slope to- 

 wards the outer sunken reef. To the south 

 of the old crater of Manga Reva the general 

 depth of the bank varies from 6 to 11 fath- 

 oms, with a deeper channel varying from 

 20 to 40 from southwest of Au Kena to- 

 wards Tara Vai. The lagoon seems to 

 form a western basin where the depth 

 varies from 10 to 20 fathoms. To the west 

 of Au Kena and Aka Maru, lying between 

 them to the line of the outer barrier reef 

 islets, a similar but shallower and flat basin 

 exists, off the northern end of Manga Reva, 

 between it and the northern horn of the 

 barrier reef, with from 7 to 11 fathoms. 

 Its rim is formed by a ring of reef patches 

 of varying size. 



On two occasions we visited the outer 

 barrier reef and examined the outer line 

 of islets of the eastern face of the Gambler 

 Islands. The position of the islets as 

 marked on the chart is not that of to-day, 

 and the position of the reef flats is not ac- 

 curate. The position of Tekava and Tauna 

 appears to be correct. Opposite Au Kena 

 and in its extension, the east face of the 

 barrier reefs projects sharply to the east, 

 forming an angular horn Avith one island 

 south of the horn and the other north, run- 

 ning at sharp angles with it, so as to form 

 a triangle which makes a deep bight open- 

 ing westward to such an extent that when 

 off the northern side of the horn we could 

 see Tekava far to the westward of it. The 

 second island is followed by a third and 

 then by an island (Taraururoa) nearly 2 

 miles long; these are separated by small 

 gaps. Then comes a larger island (Amou) 



followed by three small islands separated 

 by deep gaps. 



At Vaiatekeue (not the Vaiatekeua on 

 the chart) the reef flat becomes quite nar- 

 row; it is hardly more than 100 yards 

 wide ; the islets perhaps 50. The northern 

 islets are small and separated by long 

 stretches of low shingle and carry but little 

 vegetation and very few cocoanut trees. 

 There are but two short sand beaches all 

 the way from the northeastern to the east- 

 ern horn of the eastern face of the en- 

 circling reef of Manga Reva. A regular 

 dam of shingle from 10 to 14 feet high, on 

 the top of which the usual coral reef vege- 

 tation flourishes, extends along the inner 

 face of the reef flat, which varies from 50 

 to 150 yards in width, and is flanked at the 

 base by low buttresses of modern elevated 

 coral reef rock and of breccia, in places all 

 more or less weather beaten and honey- 

 combed. 



The islets and their formation and their 

 junction or division into larger or smaller 

 islets and the gaps which separate them; 

 the mode of formation of the buttresses, 

 of the planed-off, hard, nearly level reef 

 flat, of the coralline mounds of the outer 

 edge — all these differ in no way from what 

 has been described in other barrier reef 

 islands and atolls of the Pacific. 



The beaches of the lagoon are steep, and 

 corals do not seem to thrive in those parts 

 of the lagoon to which the sea does not 

 have access or at some distance from shore. 

 This is well shown by the vigorous growth 

 of corals in the fringing reef to the south 

 of Mt. Duff on the outer edges of the reef 

 patches of Port Rikitea, and on the spits 

 which connect Au Kena mth Manga Reva, 

 in contrast with those along the west face 

 of the lagoon flats to the west of the eastern 

 barrier reef. 



There is a northeast horn of the eastern 

 barrier reef in the extension of Manga' 

 Reva Island, forming the northern cul- 



