AGASSIZ: FIJI ISLANDS AND CORAL REEFS. 35 
atolls in Fiji. We must remember, however, that the formation of such 
atolls may also be accounted for as the result of the denudation and sub- 
marine erosion of a patch of elevated limestone, cut first into a sound, and 
then, with the disappearance of the outer rim, into a lagoon surrounded 
by a shallow reef flat ; or the same result may be accomplished from the 
wearing away of islets of volcanic origin enclosed within the outer reef, as, 
for instance, from the disintegration of the islets now left in such atolls as 
the Kimbombo Islands, Komo, and others, or of islets consisting of 
elevated limestone like the Aiwa Islands, Katavanga, Vekai, and others. 
The structure of the negro-heads occurring upon the outer reef flats, or 
their position near either a volcanic or an elevated reef region being the 
only guide as to the category to which belong such atolls as Thakau 
Mata Thuthu, Thakau Vutho Vutho, the Adolphus Reef, Dibble’s, Duff, 
and Bell Reefs, Thakau Tambu, Malevuvu, ete. 
Such a cluster as Budd Reef suggests an explanation for the for- 
mation of interior atolls, like those described by Darwin as occurring 
in the Maldive Islands, very different from the one suggested by him. 
Were Thombia cut down by erosion to the water’s edge or below, and 
changed into a small atoll, we should have a secondary atoll within the 
area enclosed by Budd Reef, and were the other small islands of the 
cluster summits of elevated limestone, and should they in their turn be 
cut down, they might form in such a large lagoon as that of Budd Reef 
other diminutive atolls, or small atolls enclosed within an atoll. Such 
interior atolls, if my view of the formation of atolls is correct, could only 
be formed in lagoons of considerable depth and size, so that the seas 
formed by the prevailing winds should have a long sweep and rise to a 
considerable height, and thus possess great disintegrating power. I shall 
refer again, when describing Vanua Mbalavu, to the probable origin of 
such great depths as forty-seven fathoms inside of the reef encircling the 
islands of Budd Reef. 
Komo. 
Plates 19°, Figs. 9-11, and Plates 22, 63-65. 
Komo Island is a narrow ridge of volcanic origin, about-a mile and a 
half in length, rising to over two hundred feet. Its western extremity is 
connected by a coral reef full of voleanic negro heads, two of which are 
mushroom-shaped and of considerable size, with the islet of Komo Ndriti, 
itself about seventy feet high. Komo lies in the southeastern horn of the 
lagoon (Plate 22) close to the southern face of the outer reef flat, from. 
