May 5, 1905.] 



SCIENCE. 



693 



mination of the central bight of the eastern 

 face of the barrier reef. From that point 

 the reef flat runs westerly to form the 

 northern horn about 3 miles north of Man- 

 ga Reva Island. The position of the outer 

 reef can not be correct on the chart (H. 0. 

 No. 2024). On leaving Manga Reva we 

 made three soundings close off the reef 

 flat line of breakers — one ofi. Tekava, at the 

 most one third of a mile from the reef, in 

 225 fathoms. Our position, plotted by 

 tangents to the volcanic islands or by their 

 summits, indicated in this case, on the 

 chart, a distance of 1^ miles. A second 

 sounding of 245 fathoms off the eastern 

 horn at less than one half mile indicated 

 on chart No. 2024 a distance of 2 miles 

 from the horn ; and a sounding of 241 fath- 

 oms one fourth of a mile off the point 

 which we had visited (Vaiatekeue) indi- 

 cated a distance of three fourths of a mile 

 on the chart. 



The slope of the Gambler Archipelago to 

 the east is steep. On coming in sight of 

 Manga Reva we sounded in 2,070 fathoms 

 at a distance of 11 miles from Mt. Duff, 

 that is, 6 miles from the outer edge of the 

 reef bearing southwest ; and on coming out 

 we sounded again half-way to that point 

 at a distance of 3:^ miles from the breakers 

 in 1,394 fathoms. 



One can not fail to be struck with the 

 similarity of the Manga Reva Archipelago 

 with the great atoll of Truk. If I remem- 

 ber rightly, Darwin also called attention 

 to this from a study of the charts. Yet, 

 owing to the ^eat size of Truk, no less 

 than 125 miles in circumference, and the 

 great distance of the barrier reef from the 

 encircled volcanic islands, the effect as one 

 steams into Manga Reva is totally different 

 from that produced by Truk. In the latter 

 some of the islands, though large, and of 

 the same height as those of Manga Reva, 

 are much more scattered, and seem of com- 

 paratively small importance in the midst 



of the huge lagoon which surrounds them. 

 The barrier reef islets of Truk are from 11 

 to 15 miles distant from the encircled vol- 

 canic islands. In Manga Reva, which is 

 only 45 miles in circumference, after pass- 

 ing the small islands in the southern and 

 open part of the lagoon when once off 

 Maka-pu, we can fairly well take in the 

 atoll as a whole. The western island (Tara 

 Vai) is only 5 miles off; Manga Reva and 

 Au Kena are about 3, as are also the islets 

 of the east face of the barrier reef; these 

 distances, as you approach the entrance to 

 Rikitea, are constantly growing less, so that 

 when in the gap between Manga Reva 

 Island and Au Kena, at "the foot of Mt. 

 Duff, none of the larger islands is more 

 than 3 miles off; and the islets of the east- 

 ern face of the barrier reef are seen to the 

 northeast about 4 miles off. When on the 

 summit of the central ridge of Manga Reva 

 one can, in a radius of a little more than 

 4 miles, take in the whole panorama of 

 Manga Reva, and get an impi-ession of the 

 relations of its different parts far better 

 than can be conveyed by the chart, for the 

 whole of the visible part of the archipelago 

 is included in a line drawn east and west, 

 south of Maka-pu ; south of that line the 

 position of the southwestern reef can be 

 traced only by the discoloration of the 

 waters. 



Manga Reva is an intermediate stage of 

 erosion and denudation, between a lagoon 

 archipelago such as Truk and a barrier 

 reef island like Vanikoro, and other islands 

 in the Society groups such as Bora Bora,* 

 Huaheine, Raiatea, Eimeo, in which the 

 surrounding platform has comparatively 

 little width and the barrier reef is close to 

 the principal island and often becomes part 

 of its fringing reef. Manga Reva is open 

 to the south and to the west, Vanikoro to 

 the east, while the volcanic islands of Truk 



* See A. Agassiz, ' The Coral Reefs of the Trop- 

 ical Pacific,' plate3 210 and 231. 



