xxviii INTEODUCTION. 



deep passes, usually most numerous on the lee side. The corals growing 

 on the sea slope of the reef platforms are often overwhelmed by sand dunes 

 blown over the land rim from the lagoon flats. 



Atolls like Tarawa, Tapeteuea, and Nonuti in the Gilbert group, and 

 Makemo, Fakarava, and others in the Paumotus, with a well-developed 

 land rim on the weather face flanked on the lee by submerged reef flats. 



Finally, such islands and islets as Tikei, Nukutavake, and a number of 

 small islands with central sinks or depressions formed by the beaches 

 thrown up on the outer edge of the flat or summit of the island, leaving an 

 open central space enclosed by the beach dams. Similar islands occur in 

 the Gilbert group, as Arorai and Tamana ; Mejit, Lib, and Jemo in the 

 Marshall, and Niu-akita and Nanomana in the Ellice groups. 



The soundings taken by the "Albatross" in the Marquesas show that 

 two of those volcanic islands are connected by a plateau with a depth of 

 800 fathoms (PI. 200, Stations 24-28, p. 380). The soundings in the Pau- 

 motus (PI. 201, Stations 34-60, 70-120, p. 380) developed the plateau from 

 which the northwestern islands of the group rise,^ a plateau with a depth 

 of about 800 fathoms. The soundings among the central and eastern 

 Paumotus developed smaller plateaus or spurs uniting adjoining atolls, and 

 also showed that the eastern atolls and islands are separated by channels 

 of great depths (PI. 201, Stations 122-172, p. 385). 



The Society Islands are also separated by deep channels (PI. 202, Sta- 

 tions 65-75, p. 382), and deep soundings separate the Cook Archipelago 

 from Nine and Tonga (PI. 211, Stations 181-187, p. 388). 



In Tonga the general depth of the three component plateaus is about 

 fifty fathoms ; the plateaus themselves are separated by channels with not 

 more than 250 fathoms (Pis. 213, 214) ; the land masses of Tongatabu, 

 Haapai, and Vavau slope gradually into the general level of their respec- 

 tive plateaus, and the scattered islands of Nomuka rise very gradually from 

 the main plateau at a depth of twenty-five to thirty fathoms. 



Somewhat shallower water exists between Tonga and Fiji (PI. 213, 

 Station 188, p. 388) than between Niue and Tonga. The soundings in the 

 channel between Yangas^, Mothe, and beyond indicate the shallower 



1 See p. 25, Figs. 1-12. 



