AGASSIZ: LETTERS TO THE HON. GEORGE M. BOWERS. 77 



a fringing reef flat ^vhich runs around the west face of Aka Maru ; Au 

 Kena is also edged by an extensive fringing 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 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 Cemetery, leaving a narrow but deep pass for the entrance 

 of ships into the inner harbor of Rikitea. There is only from 1 to 2J 

 fathoms of water on these two spits. 



The depth of the basin within this area with from 25 to 31 fathoms 

 would be naturally explained as being part of an ancient crater, as in 

 Totoya in Fiji ; its northeastern rim is also perhaps further indicated by 

 the comparatively shallow flat of the lagoon to the west of the barrier 

 reef, with from 5 to 1 1 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 main ridge of Tara 

 Vai is the edge of parts of three craters now opening to the west. The 

 four small volcanic islands in the southern part of the lagoon are isolated 

 fragments, steep to, greatly weathered, and disintegrated. No sound- 

 ings 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 towards the outer sunken reef. To the south 

 of the old crater of Manga Reva the general depth of the banks varies 

 from 6 to 1 1 fathoms, witli a deeper channel varying from 20 to 40 from 

 southwest of Au Kena towards 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 and the line of 

 the outer barrier reef islets. A similar but shallower 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 very 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 correct. The position of Tekava and Tauna appears 



