May 5, 1905.] 



SCIENCE. 



691 



the reef extends in an indefinite narrow 

 ridge 8 miles long, with from 3 to 8 fath- 

 oms, in a southeasterly direction. The 

 western edge is steep to, and the eastern 

 face passes gradually into the lagoon, 

 which at that point has a general depth of 



8 to 20 fathoms. The deepest part of this 

 region is at the foot of Mt. Mokoto between 

 it and Tara Vai, though Tara Vai is united 

 with Manga Reva Island by a plateau vary- 

 ing in depth from 3^ to 4^ fathoms. ■ 



At the southeastern point of the reef it 

 passes into a wide plateau with from 9 to 

 10 to 15 fathoms. This plateau is about 



9 miles wide southwest of Tekava. That 

 part of the atoll has not been well sur- 

 veyed, so that the position of the reef flat 

 has not been ascertained further west on 

 that part of the east face; but the south- 

 east passage indicates 5^, 6 and 6^ fath- 

 oms, where it probably marks the south- 

 western extension of the eastern barrier 

 reef, separating the lagoon from the south- 

 ern plateau to the south of the encircling 

 reef. 



The western face of Manga Reva and 

 of Tara Vai are indented by deep bays, 

 which are formed by spurs running from 

 the central ridge of these islands, the rem- 

 nants probably of small craters which 

 flanked the large crater, of which Manga 

 Reva forms the western rim and Au Kena 

 is the remnant of the southeastern edge, the 

 former extension of this rim being indi- 

 cated by the spits uniting the base of Mt. 

 Duff with Au Kena ; and by the projection 

 of Au Kena towards the outer barrier reef, 

 and of the numerous patches of coral reef 

 off the northeast point of Manga Reva 

 towards the outer line of motus until they 

 almost unite with the barrier reef. 



The whole of the western bays of Manga 

 Reva Island is filled with fringing reefs 

 which leave but here and there a deeper 

 pass to the shore. The south face at the 

 foot of the bluff of Mt. Mokoto and Mt. 



Duff is edged by a flourishing fringing 

 reef, which extends nearly half a mile on 

 the plateau at their base. The port of 

 Rikitea is a reef harbor formed within the 

 large fringing reef which occupies the 

 whole of the southern bay of Manga Reva 

 Island. The east face of Tara Vai and 

 part of the east and of the west face of 

 Aga-kanitai are also fringed with reefs. 



The islets and the islands of Aka Maru, 

 Makiro and Makapu are within a fringing 

 reef flat which runs around the west face 

 of Aka Maru ; Au Kena is also fringed by 

 an extensive reef which runs out in a spit 

 of more than half a mile in a northeasterly 

 direction almost to the outer line of motus, 

 which are nearly united with it by these 

 irregular patches. To the west of Au Kena 

 a huge spit of 2 miles in length extends 

 towards the base of Mt. Duff and almost 

 unites with the fringing reef off the Ceme- 

 tery, leaving a narrow but deep pass for 

 the entrance of ships into the inner harbor 

 of Rikitea. There is only 1 to 2f fathoms 

 of water on these two spits. 



The depth of the basin within this area 

 with from 25 to 31 fathoms would be nat- 

 urally explained as being part of an an- 

 cient crater, as in Totoya in Fiji ; its north- 

 eastern rim is also, perhaps, further indi- 

 cated by the comparatively shallow flat of 

 the lagoon to the west of the barrier reef, 

 with from 5 to 11 fathoms of water. 



The principal islands of the group are 

 in the central part of the lagoon. The 

 four larger islands are Manga Reva, Tara 

 Vai, Au Kena and Aka Maru. Tara Vai 

 is flanked by Aga-kanitai and another islet 

 to the west called Topunui; Aka Maru is 

 flanked by Mekiro to the north and by 

 Maka-pu to the south. The southeast face 

 of Aka Maru is an extinct crater, of which 

 Maka-pu forms the south rim. The mair 

 ridge of Tara Vai is the edge of parts 

 three craters now opening to the west. The 

 four small volcanic islands in the southern 



