xxvi INTRODUCTION. 



as well as the Solomon,' New Hebrides, and Oahu in the Sandwich Islands, 

 are partly flanked by elevated coralliferous limestone. 



Next may come smaller volcanic islands with barrier and fringing reefs, 

 like the Pelew Islands, Yap, Truk, Ponapi, Kusaie ; the smaller New 

 Hebrides and Fiji Islands, like Nairai, Makongai, Mbengha ; the volcanic 

 islands of the Cook group, as Aitutaki, Rarotonga ; the Home Islands, 

 Roturaah, the Marquesas, and such islands as Maupiti, Bora Bora, Raiatea, 

 Huaheine, Eimeo, in which the area of encircling reefs is as large, if not 

 larger, than the enclosed volcanic mass. 



Volcanoes like Totoya and Thombia in Fiji show the possibility of the 

 formation of an atoll-like island by the growth of corals on the submerged 

 or denuded rim of an extinct volcano, enclosing a central basin: the old 

 crater of the volcano. In Totoya the extension of the volcanic reef rim 

 forms a barrier reef surrounding the island and enclosing a barrier reef 

 lagoon, with ship passes leading into it. 



Niuafou and Tofua in Tonga are both islands with extinct craters filled 

 with brackish water. Were the rim cut down to below the level of the sea, 

 they would become reef flats enclosing a deep lagoon, as is the case with a 

 part of the rim of Thombia and Totoya. 



Elevated coralliferous limestone islands, probably of tertiary age, with lim- 

 ited areas of narrow reef flat platforms, like Makatea, Nine, Nauru, Paanopa, 

 Naiau, Wangava, with ill-defined sinks or basins occupying part of the summit. 



Elevated corallifei-ous limestone islands, like Mango, Kambara, Tuvutha, 

 in which the sink is better defined and where a volcanic outburst has 

 broken through the rim or central part of the sink or both. 



Elevated islands of coralliferous limestone, like Fulanga, Yangasa, Ongea, 

 where the sea has eaten through the limestone rim towards the inner sink 

 cutting the rim into islands, and has formed a sound or lagoon dotted 

 over with limestone outliers forming undercut and weathered islands and 

 islets. The encircling land rim may disappear or be reduced to a few 

 heads, as in Argo, Ongea, or Yangasa. 



^ Dr. Guppy has given an excellent account of the geology of the Solomon Islands. He was the 

 first to call attention to tlie great importance of the comparatively thin elevated coral reefs of those 

 islands and to the e.xistence in the Pacific of underlying calcareous rocks probably of tertiary age. 

 "The Solomon Islands: their Geology ... by H. B. Guppy. London, 1887." 



