108 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
Islands has a crater with a depth of nearly 450 fathoms, while many 
smaller peaks, some of fully 1,200 feet rise from its bottom, and its 
diameter is fully as great as that of many of the larger atolls of the 
Fijis. So that, at any rate in a volcanic district, the great depth of 
some of the atolls cannot now be considered as a proof of the theory of 
subsidence. 
A still larger extinct crater than Haleakala is that of Aso San in Japan, 
and in Java there are many craters of dimensions fully equal to those 
of a number of Fiji atolls. 
In addition to Thombia and Totoya, we found at Moala the rim of an 
extinct crater forming the deep bay on the east side of the island (Plates 
16, 56). The longest diameter of this crater must have been fully 
three miles, and had the denudation of the island been carried on some- 
what further, so as to eat away the low western rim of the crater (Plate 
56) and connect the deep bay of the east face (the extinct crater) with 
the indentation on the west of the island, it would be difficult to detect 
the existence of a former extinct crater from the narrow ridge or island ~ 
which would rise in the eastern part of the lagoon (Plates 16, 56). 
Kriimer? has attempted to account for the elongated outline of so 
many of the atolls of the Paumotu, Caroline, Marshall, Gilbert, and 
Ellice Islands, upon the theory that they owe their origin to submarine 
hot springs and volcanic eruptions, the material of which was distributed 
by the trend of the great oceanic currents in the general directions 
indicated by these island groups. 
While granting that volcanic agencies have raised the coral islands of 
the Pacific, we must remember that the shape of the islands and their 
extent are due to the size of the plateaus of submarine erosion which form 
the banks upon which coral reefs have grown. Undoubtedly the sub- 
stratum of many of the atolls may have been formed of volcanic ashes by 
eruptions similar to that which has thrown up Falcon Island, and which 
has been fully described by Lister.? Yet the great majority of the vol- 
1 Bau d. Korallenriffe, p. 88. 
2 J. J. Lister, A Visit to the newly emerged Falcon Island, Tonga Group, South 
Pacific. Proc. Roy. Geog. Soc., 1890, Vol. XII. p. 157. 
The island (Falcon) is composed of fine-grained dark grayish material, arranged 
in strata. “A bare brown heap of ashes round which the great rollers break and 
sweep the black shore in sheets of foam.” The eruption occurred four years ago; 
its present height is 153 feet. “ Considering how rapidly the island is being covered 
by the action of the waves, it is evident that in a few years .. . it will have disap- 
peared beneath the surface of the ocean. . . . Some distance to the east of it lie two 
islands, Namuka iki and Mango, and these islands have been elevated before any 
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