NORTH MAHLOS BANK, 167 
at 6 to 7 fathoms and seldom exceeding 10 fathoms in height. On it may be seen from 
the surface masses of Madrepora, and dredges and trawls come up off reef after reef, 
either torn to pieces or nearly full of Goniopora, <Alveopora, Dendrophyllia and other 
corals. Other organisms too are numerous; Alcyonarians and Gorgomians are constantly 
brought up, and the dead corals from the reef above are protected from solution by 
Polyzoa, Tunicata, Polytrema, and many other incrusting animals. A further character 
is that, from the edge of the reef-flat to the edge of the steep off such a reef, the 
whole bottom is covered with a dense grove of corals, while off a reef in Haddumati 
or an enclosed atoll this area is almost bare save for a few masses of Lobophytum and 
a little Halimeda. 
In Mahlos both conditions are found at the present day, that of the enclosed lagoon 
in the central mass of reefs, and that of the open bank to the north round Limbo-Kandu 
and the neighbouring reefs. Round the latter reefs the slope is covered with corals and 
other organisms to a depth of about 6 fathoms, at which depth the steep commences 
only to fall to about 14 fathoms, being in some places scarcely defined at all. The reefs 
near Limbo-Kandu are undoubtedly extending outwards on all sides, but it is evident 
that the above island exercises a by no means helpful influence on its own reef, as the 
first slope from which the rate of the extension may be judged, is broader off the various 
faro in the vicinity, and the steep is less marked. In the “giri atiri” or “jungle of 
reefs” in the centre of North Mahlos the conditions are far otherwise. The steep is 
everywhere well-defined and the upper slope, until it absolutely passes into the flat, is 
as described above in closed atolls quite bare of corals. Any corals brought up from the 
base of the steep are bored into and rotten, and without any protecting organisms. 
Everything appears to be covered with a thin coat of slimy mud clinging to it, and 
the reef-flat above is sometimes undermined for a fathom or more. Here and there great 
masses of the reef have fallen—the sea has not the power within a bank to throw them 
back on to the reef as negro-heads\—and seem to be rotting away. ‘The process is at 
the same time so slow that it is difficult to prove except by a series of most accurate 
observations through many years, that any reef is actually washing away, but the general 
impression in the “jungle” is that the reef-flat is everywhere being driven back, and that 
the whole of its reefs are being removed. I do not see that the characters of its reefs 
can be otherwise explained, and later I propose to show some definite evidence that there 
has been loss in the inner reefs of the western faro. The last stage in the history of 
a disappearing reef is its reduction to a mere little surface patch or series of patches, 
ultimately single coral heads, which sooner or later will themselves topple over, their basal 
mounds being subsequently reduced to the level of the floor of the bank. The topographical 
relations and depths between many of the shoals in the “jungle” show clearly their former 
connection in single reefs or faro. The last stages it must be remembered are necessarily 
much slower than the first, as with progressive destruction of the reefs more open conditions 
prevail, and there is less mud. Even a condition of stable equilibrium may be found, and 
this I deem to be the case in many of the more open, larger and more perfect atolls. 
In the smaller such a condition cannot be reached, and hence we find the open lagoons 
1 IT restrict the use of the term “negro-heads” to large _ the reef-flat. I never saw any such in the Maldives, though 
masses of the rock, which have been broken off the edge of they were common enough on Fijian and other Pacific Ocean 
any reef by hurricanes or heavy gales and thrown back on to reefs. 
G. De, 
