AGASSIZ : FIJI ISLANDS AND CORAL BEEFS. 109 



canic islands which abound in the coral reef districts of the Pacific do 

 not consist of such easily scattered material. In addition, it is well 

 known that many of the islands are composed of elevated coralliferous 

 limestones, and that is probably the composition of the substratum of 

 many of the atolls of the Paumotu, Ellice, Gilbert, Tonga, and Fiji groups. 

 They indicate the existence of more or less extensive submarine ridges 

 composed either of limestone or of volcanic rocks, and not necessarily 

 peaks or summits formed of volcanic ash and spread out by the action 

 of the currents, as has been mapped out by Kriimer.^ Nor do we know 

 enough of the configuration of the bottom to justify the statement that 

 the atolls of a group are not sepai'ated by great depths such as separate 

 the islands of the Samoan group. The soundings round Funafuti by 

 the " Penguin," and others near Tonga and in Fiji (Plate l), do not 

 confirm Ki'amer's views. 



The old view entertained by Chamisso regarding the mode of origin of 

 the substratum iipon which coral reefs are built does not greatly differ 

 from thfit which we have applied to the formation of coral islands in 

 Fiji. We have laid greater stress upon denudation and submarine 

 erosion after elevation by volcanic agencies, while Chamisso ^ accepts 

 the uplifting of the insular masses to the level at which coral begins 

 to grow. 



considerable thickness of coral grew upon them. They are formed by stratified 

 volcanic material deposited under water, and are now surrounded bv broad coral 

 reefs. In them we may read the possible future history of Falcon Island. If no 

 elevation takes place, the stones and debris will give a resting place to a host 

 of marine animals and plants, . . . and another fine island will be added to those 

 summer seas." Recent volcanic action in Tonga and in Samoa does not seem to 

 have prevented there the formation of extensive coral reefs, as has been suggested 

 by Dana. 



1 Loc. cit., pp. 95-97. 



- " Wir denken uns eine Inselgruppe dieser Bildung als eine Felsenmasse, die 

 sich mit senkrechten Wanden aus der unermesslichen Tiefe des Oceans erhebt und 

 oben, nahe an dem Wasserspiegel, ein iiberflossenes Plateau bildet. Ein von der 

 Natur rings um am Rande dieser Ebene aufgefiihrter breiter Damm, wandelt 

 dieselbe in ein Becken um. . . . Er ist da Stellenweise unterbrochen und seine 

 Liicken bieten oft selbst grosseren Schiffe Fahrenge dar. . . . Innerhalb dieser 

 Thore liegen ofters einzelne Felsenbanke. . . . Andere ahnliche Banke liegen hie 

 und da im Innern des Becken zerstreut." Kotzebue, Reise, Bd. III., Bemerkungen 

 und Ansichten, 1826, von Adelbert v. Chamisso, p. 106. Chamisso gives an 

 admirable account of Radack Ralick, and of the fauna, flora, and general aspect of 

 this low coral island. 



