AGASSIZ: FIJI ISLANDS AND CORAL REEFS. 105 
Lendenfeld } gives altogether too great prominence to the part played 
by dry atolls. They do not occur anywhere except as most diminutive 
atolls. The only atoll in Fiji which answers at all to the theoretic 
requisitions of Lendenfeld is that of Vuata Vatoa (Plate 23%, Fig. 4), 
near Turtle Island, in Lau. I have not visited the island, and my 
impression is taken from the chart” and the Sailing Directions where 
it is described. Yet even that atoll has outfalls on the northwest side, 
and the margin is awash at high water, evidently allowing large masses 
of water to be poured into the lagoon, so that further denudation and 
erosion must eventually so modify this atoll that there will be a larger 
and more open lagoon than formerly, and it will not fill up as is required 
from the other point of view. 
EXTINCT CRATERS AND ATOLLS. 
There is, however, still another phase in the formation of atolls 
which has received but little attention, and that is the influence of the 
denudation and erosion of velcanic summits or ridges, or of extinct 
craters, in the formation of atolls. There are in the Fijis two extinct 
craters which are most interesting. One of these is the small extinct 
erater of Thombia in the Ringgold Islands (Plates 18,70). The highest 
point of its rim, the exterior circumference of which is nearly two miles, 
is nearly 600 feet, and it is continuous with the exception of a small 
part of its eastern edge, about a fifth of a mile, across which a coral reef 
extends, the extension of the fringing reef surrounding the island closing 
the entrance to the crater; the enclosed basin has a depth of 24 
fathoms. The other extinct crater is that of the island of Totoya 
(Plates 16, 22, 66-69), an isolated peak in the southern part of the 
group. It is about six miles in diameter, with an inner basin of three 
miles in diameter and a depth of over thirty fathoms. The highest 
point of the rim is 1,200 feet, and at two points the rim is low, forming 
in one case a narrow isthmus separating the crater basin from the outer 
lagoon. The horns of the open rim are connected by a coral reef, over 
which thunders the Pacific swell, piling up the water into the great 
basin of the crater. This water finds its way out through an opening 
called the Gullet, which, though narrow, forms an excellent passage into 
the anchorage inside of the crater. This island has not only a fringing 
1 Nature, June 12, 1890, p. 148. 
2 Admiralty Chart, Plan 742. 
