CORAL REEFS AND SUBMARINE BANKS 211 
in the unconformable contact of an elevated and much dissected 
reef on its sloping volcanic foundation in the island-of Vanua 
Mbalavu of the Fiji group;’ hence subsidence there seems undoubt- 
able. ; 
Moreover, if three unconformable elevated reefs, B’, B’’’, B’’, 
stand in terraced arrangement, the sea-level being at S., it is by 
no means necessarily the case that they were formed during pauses 
in the elevation of their foundation, as has often been supposed: 
for their unconformity shows that a period of erosion followed by 
submergence must have taken place before emergence; hence the 
reefs may have been formed during pauses in submergence. If their. 
structure is such as is shown in Fig. 1, B’’”’ being superposed on the 
upper surface of B’ and apposed on the front slope of B”, then the 
lowest reef must have been formed during an early pause in sub- 
mergence, the highest reef at the climax of submergence, and the 
middle reef during a pause in emergence. If the changes of level 
thus indicated are of greater measure than 250 feet and are 
unlike on neighboring islands, they must be ascribed chiefly to 
local subsidence and upheaval and not to changes of the ocean 
surface around still-standing islands. 
The structural relations of elevated reefs have seldom been 
observed in sufficient detail to determine the sequence of their 
formation; some unconformable terraced reefs that I examined 
on the island of Efate, New Hebrides, of which the highest was 
about 800 feet above sea-level, seemed to be superposed on one 
another, suggesting that they were formed during pauses in sub- 
sidence and afterward elevated. 
It is not, however, only for elevated reefs that the test of 
unconformable contacts is of service. Many sea-level fringing 
reefs, occurring either at the inner border of barrier-reef lagoons, or 
alone fronting the ocean, have manifestly unconformable contacts 
with the eroded rocks of the coast that they border. This is 
repeatedly the case with the fringing reefs of volcanic islands, and it 
is even more clearly the case with the fringing reefs on coasts of 
deformed and eroded continental rocks, like those of New Caledonia, 
Queensland, and elsewhere. Wherever the volume of erosion 
« “The Origin of Certain Fiji Atolls,” Proc. Nat. Acad. Sci., II (1916), 471-75. 
