AGASSIZ: FIJI ISLANDS AND CORAL REEFS. 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 Kramer.t Nor do we know 
enough of the configuration of the bottom to justify the statement that 
the atolls of a group are not separated 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 1), do not 
confirm Kramer’s views. 
The old view entertained by Chamisso regarding the mode of origin of 
the substratum upon which coral reefs are built does not greatly differ 
from that 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 
voleanie material deposited under water, and are now surrounded by broad coral 
reefs. In them we may read the possible future history of Falcon Island. If no 
elevation takes place, the stones and débris 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 Loe. cit., pp. 95-97. 
2 “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 grésseren Schiffe Fahrenge dar. . . . Innerhalb dieser 
Thore liegen ofters einzelne Felsenbiinke. . . . Andere ahnliche Binke 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. 
