APRIL” 15,1905) 
NATURE 
19t. 

mergence during subsidence may have been almost 
neutralised by the lowering of the sea-level during 
the oncoming of a glacial epoch, and under such 
conditions coral reefs would broaden and lagoons 
would become shallow; but with the passing of a 
glacial epoch the return of ice-sheet water to the ocean 
would accelerate the submergence due to subsidence, 
and at such a time, coral reefs might be more or 
less completely drowned; thus the discontinuity 
of certain reefs on so-called ‘‘platforms’’ may be 
explained. 
All the phenomena which testify to the formation 
of coral reefs on subsiding foundations can be equally 
well explained by the assumption of a rise of the ocean 
surface around or over fixed foundations; but a rise 
of the ocean surface in any coral-reef region demands 
a rise of the whole ocean surface; and if the coral-reef 
foundations are to stand still, a rise of the whole ocean 
surface can be explained only as the diminished result 
of a greater rise of the ocean floor in some non-coral- 
reef region. The conditions involved in this alterna- 
tive for the simple theory of local subsidence are so 
extravagantly improbable that, as soon as they are 
explicitly defined, they must be rejected. 
No absolute demonstration of the origin of coral 
reefs, or, for that matter, of any other geological 
structure, is possible; the most that can be hoped for 
is a highly probable conclusion. The conclusions 
announced above in favour of Darwin’s theory are 
believed to have about the same order of probability 
as that usually accepted as ‘“‘proof’’ in geological 
discussions. 
A number of local 
announced as follows :— 
The elevated reef along the south coast of Oahu, 
Hawaii, was formed during or after a sub-recent 
period of subsidence. for its limestones enter well- 
defined valleys that must have been eroded when the 
island stood higher than now, and before the reef- 
limestones were deposited in them. 
The Fiji group has suffered various movements of 
subsidence and elevation by which its many islands 
were affected in unlike ways. Elevation has taken 
place at different times in different islands, for some 
of the elevated reefs are elaborately dissected, others 
are very little dissected, and still others remain at 
sea-level. The embayments due to the latest sub- 
mergence of the larger islands, Viti Levu and Vanua 
Levu, are now largely filled with delta plains. All 
the reefs, those now elevated as well as those at sea- 
level, appear to have been formed during periods of 
subsidence; the evidence afforded by the elevated 
reefs of Vanua Mbalavu, Mango, and Thithia is 
specially significant on this point. The medium-sized 
island of Taviuni has few visible reefs, because its 
flanks and shores are flooded by sheets of recent lava. 
The small island of Wakaya seems to be a tilted 
block of lava beds, not a dissected volcano. 
The extensive barrier reef of New Caledonia has 
grown up during a recent subsidence by which that 
long and maturely dissected island has been much 
reduced in size and elaborately embayed; but unlike 
most encircled islands, this one was strongly cliffed 
around its south-eastern end, and along much of its 
north-eastern side before the recent subsidence took 
place. 
The two south-eastern members of the Loyalty 
group, Maré and Lifu, are former atolls, evenly up- 
lifted about 300 ft.; Maré shows a small hill of 
volcanic rock in the centre of its limestone plateau 
or elevated lagoon floor. Uvea, the north-western 
of the three Loyalty islands, is a slightly tilted atoll; 
its eastern side shows an uplifted reef in rudely cres- 
centic form, which reaches a height of too or 200 ft. 
NO. 2372, VOL. 95] 
conclusions may 
be briefly 

at the middle of its crescent, and slowly descends to 
sea-level at its horns; a bight in its convex front may 
be the result of a landslide; the tilted lagoon floor 
slowly deepens westward and is enclosed by dis- 
connected, upbuilt reef-islands. 
The New Hebrides show signs of uplift in their 
elevated reefs, and of depression in their embayments. 
There is some evidence that certain uplifted fringing 
reefs on the island of Efaté, near the centre of the 
group, were formed during pauses in a subsidence that 
preceded their uplift, and not during pauses in their 
uplift as inferred by Mawson. ‘The narrowness of 
the lagoons enclosed by the barrier reefs that encircle 
certain strongly embayed islands in this group may 
be explained by supposing alternations of slow and 
rapid subsidence; thus the earlier-formed reefs, which 
began to grow when the subsidence was _ slowly 
initiated, were drowned when it was later accelerated ; 
and new reefs, thereupon begun on the shore line of 
that time, now, after a second period of slow subsi- 
dence, stand near the present shore line, though the 
shore line is strongly embayed, because the total sub- 
sidence has been large. The absence of reefs around 
the island of Ambrym is due to its abundant eruptions 
in recent time, the latest one being in December, 
1913; scattered corals were seen growing on one of 
its sea-cliffed lava-streams, thus illustrating the initial 
stage of a fringing reef. 
The Great Barrier reef of Australia, the greatest 
reef in the world, with a length of some 1200 miles 
and a lagoon from 15 to 70 or more miles wide, has 
grown upward during the recent subsidence by which 
the Queensland coast has, after a long period of still- 
stand, been elaborately embayed, as was pointed out 
by Andrews in 1902. A very recent uplift of some 
ro ft. has occurred, as was long ago noted by Jukes. 
There is much reason for believing that a broadened 
reef-plain, with extensive land-fed deltas along the 
continental margin, had been formed before the recent 
subsidence took place; and-it is this broadened reef, 
now submerged, that is thought to form the ‘plat- 
form’? on which the Great Barrier reef has grown 
up. Guppy’s suggestion that the platform or ‘“ sub- 
marine ledge’ is due to marine abrasion, before coral 
reefs were established here, and that no subsidence 
has taken place, cannot be accepted. It is highly 
probable that the well-attested recent subsidence was 
due to a gentle flexure, by which the offshore sea- 
bottom was bent down: and, if so, the coastal sub- 
mergence will give too small a measure of the thicl- 
ness of the distant barrier reef. In this respect the 
Great Barrier reef along the shore of a continent 
differs significantly from smaller barrier reefs around 
oceanic islands, in which the subsidence of the island 
and its reefs are essentially uniform. 
A few hours on shore at Raratonga, the southern- 
most member of the Cook group, sufficed to show 
that extensive embayments formerly entering its 
elaborately carved mass are now occupied by delta 
plains and perhaps in part by slightly elevated reef- 
and lagoon-limestone. 
Five islands of the Society group exhibit signs of 
recent subsidence in their intricately embayed shore 
lines, as has lately been announced by Marshall. A 
sixth, the cliff-rimmed island of Tahiti, the largest 
and youngest of the group, suffered moderate subsi- 
dence after its cliffs were cut, but the resulting bays 
are now nearly all filled with delta plains, which often 
advance into the narrow lagoon; hence a pause or 
still-stand has followed its latest subsidence. All the 
barrier reefs of this group appear to have been formed 
during the recent subsidence that embayed their cen- 
tral islands. 
W. M. Davis. 
