478 
GEOLOGY: W. M. DAVIS 
forms here given does not, to my reading, support his view that the 
uplifted limestone islands were not atolls of an earlier generation. 
Indeed it is a good deal of an assumption that Great Argo reef, a true 
atoll today, has ever been uplifted, for it contains no limestone islands: 
the reason for supposing it to have been uplifted is, that limestone 
islands, mere remnants of formerly larger masses, occur inside of the 
neighboring barrier reefs. But if Great Argo reef represents an uplifted 
and worn-down atoll, its upKft must have been relatively early because 
its erosion is completed; and if its uplift were early, its previous abrasion 
must according to the Glacial-control theory, have been accompKshed in 
much less than the whole of the Glacial period; yet this is the largest 
atoll in Fiji. 
A sixteenth example might be added, farther north than the others 
and about on the meridian of the maturely dissected limestone islands, 
although in its original form before uplift it appears to have been not 
a true atoll, but an almost-atoll: that is, a reef enclosing a lagoon in 
which a small volcanic island still survived. This is the group of 
islands, of which Vanua Mbalavu is the largest, enclosed by the great 
Exploring reef, some account of which has been given in an earlier 
article (these Proceedings, 2, 1916, 471-475). The original sea- 
level outline of this almost-atoll reef appears to have enclosed a large 
and irregular lagoon, 15 by 25 miles in diameter, in the western part of 
which a small volcanic ridge rose in Pliocene or Pleistocene time to a 
height of 200 or 300 feet: after an uplift of over 600 feet, the limestone 
plateau was greatly eroded, and reduced for the most part to moderate 
or small relief, so that in Pleistocene time its larger and higher surviving 
fragments, partly limestone, partly volcanic, were but a small fraction 
of the original mass; then the resulting lowland was submerged, and the 
present barrier reef was built up around its margin; but be it noted 
that this recent submergence cannot be fully accounted for by the 
Postglacial rise of ocean level, because the enclosed lagoon floor deepens 
from 20 fathoms near its western side to over 100 fathoms at its eastern 
side, thus implying a recent tilting, as Agassiz noted; and this tilting 
would represent the sinking side of the wave-like upheaval above 
mentioned. The surviving islands are pertinent in the present con- 
nection because several of them show volcanic rocks unconform- 
ably covered by eroded limestones, remnants of the uplifted almost- 
atoll: the contact of the two kinds of rock is not a level platform 
at a depth of about 240 feet below the highest limestones; on the 
contrary, the contact exhibits rounded forms and moderate slopes 
such as characterize volcanic islands maturely dissected by subaerial 
