GEOLOGY: W. M. DAVIS 
477 
atolls were available for high-standing oceanic limestone islands, these 
examples might be ascribed to it; but in the absence of other origin, 
it seems reasonable to regard them as maturely dissected atolls. They 
must have been uplifted earlier than their little-dissected neighbors, 
probably during the Glacial period and not after its close. It is here 
noteworthy that the surrounding sea-level reefs are relatively distant 
barriers. Two other examples, North Argo and Reed, take their 
names, not from the Httle islands that they enclose, but from the en- 
closing reefs themselves: they lie farther east than the others and are 
classed today as almost-atolls ; one of the islands in the North Argo 
lagoon is ''stated to be of volcanic origin;" both islands in the Reid 
lagoon are "probably of elevated limestone." Finally, Great Argo 
reef is a true atoll, the largest of its kind in Fiji. It is noteworthy that 
these islands are so distributed as to indicate a westward wave-Hke 
progression of a meridional belt of upheaval, so that the earliest up- 
lifted reefs, all lying to the eastward, are at present greatly dissected and 
somewhat depressed, while the latest uplifted reefs, all lying to the west- 
ward, are little dissected; farther west still a number of islands show 
no signs of uplift, as if the wave of uplift had not yet reached them. 
Now although the first ten islands of the table are higher than 240 
feet, they do not exhibit any volcanic foundation. The first five of 
these are, however, so little dissected that the volcanic foundation, if 
above sea-level, may be concealed by its limestone cover. The absence 
of a volcanic foundation in the next five argues strongly against the 
Glacial- control theory; for in Fulanga, although the reef rim is not 
much dissected, the enclosed area has depths of 4 or 5 fathoms in its 
lagoon, the bottom of which is thus 290 feet below the rim crest; Tuvutha, 
which reaches the exceptional height of 800 feet in its northern part, 
reveals no volcanic platform at or below a height of 500 feet in its 
center; Namuka, Ongea, and Yangasa, more dissected and embayed 
than the hypothetical island of sector H, figure 3, show no volcanic 
platform, although the vertical measure from their somewhat aggraded 
lagoon floors to their somewhat worn-down summits ranges from 330 
to 500 feet; this is^mply sufficient to reveal a volcanic platform if it 
occurred at the depth of 240 feet below the original reef -level of the now 
dissected islands. Aiwa and Oneata, small limestone islands in rather 
large lagoons, although they have undoubtedly lost something of their 
original height, have vertical measures of 350 and 280 feet between 
lagoon floor and island top. The three remaining examples are ad- 
mirable illustrations of Agassiz' theory that some atolls are derived 
from upKfted and worn-down limestone islands; but the sequence of 
