AGASSIZ: FIJI ISLANDS AND CORAL REEFS. EE, 
inlength. From the extremities of the islands off the south face projects 
a horn of the outer reef, forming a small enclosed lagoon separated from 
the principal lagoon and with a greatest depth of ten fathoms. The 
greatest depth of the principal lagoon is 23 fathoms. The northern face 
of the outer reef is much broken, and flanked by large patches of corals 
and heads, with a wide entrance into the northwestern end of the lagoon. 
The western face of the lagoon is three miles long. The inner edge of 
the western face is flanked by a broad belt of coral patches and heads. 
The coral patches are growing upon sunken heads of elevated reef rock, 
the remnants of the elevated reef once covering the area now occupied 
by the Aiwa lagoon. The reef flats consisted wherever we saw them of 
elevated reef rock planed off to a general level, upon which coral patches 
were growing. 
This group is historically interesting, as Dana in his Corals and Coral 
Islands (p. 264) gives a section across the islands and lagoon, which 
according to him illustrates very forcibly the effect of subsidence in 
the formation of -atolls. A more unfortunate selection could not have 
been made. But Dana did not visit this group, and took his information 
from the charts, or he would not have chosen as an illustration an island 
group which consists of elevated limestone rock,— islands which after 
their elevation have suffered most extensive denudation and erosion, and 
upon the outer edge of the surrounding platform the corals of the present 
epoch have found a footing and formed a sheet of very moderate thick- 
ness. The lagoon between the encircling reef and the islands has 
been hollowed out by mechanical causes similar to those which I have 
alluded to elsewhere, and which have in my opinion shaped the lagoons 
of all the atolls and barrier reefs of the Fijis. 
Dana assumes the lagoon of Aiwa to have been formed during the 
slow subsidence of the island enclosed within its reef, while there is every 
evidence that the lagoon of Aiwa has been scooped out by submarine 
erosion, and the island, consisting of late tertiary limestones, has been 
lowered by denudation, and that the limestones after their elevation have 
remained at the present level, and that the corals now growing upon the 
outer rim and upon the reef flats, as well as the coral heads inside of the 
lagoon, have but little thickness, and that well within the greatest depth 
at which reef-building corals can grow. 
