THE FORMATION OF THE MALDIVES AND LACCADIVES. 179 
and perhaps deserves a more precise notice here. Of first importance so far as massiveness 
is concerned may be placed Heliopora, which I obtained off Funafuti from the same depths. 
In all four dredgings outside Addu atoll it was obtained, and from the quantity procured 
seemed extremely abundant; it too was not bored into by organisms in any way. ‘The 
genus is also found living in the lagoons of atolls in the Maldives, but I never saw it 
living on the reef-flat or outer slope to 15 fathoms. In the lagoons the colonies are closely 
packed with lamellae and stunted. Of true corals in this class (Madreporaria) many large 
masses of Goniopora and Alveopora of several species were brought up from the lagoons, and 
solitary corals were in places extraordinarily numerous. Cycloseris was found on nearly every 
bank, and in one of the north passages into Suvadiva atoll with 38 fathoms of water were 
trawled great masses of rubble, formed almost entirely of its dead coralla. The most 
important genus however was Dendrophyllia’, of which a very dark green velvety species 
(D. ramea, sp.?) formed great dense groves in nearly every passage into the interiors of 
the banks. We never obtained it below 45 fathoms, nor above 15, but between these depths, 
if the bottom was at all rocky, the dredges seldom came up without some of its branches. 
Many other corals could doubtless be added to this list, but the above seemed the most 
Important forms in the Maldives, which might be expected to raise the reefs in their later 
stages, and afford foundations for the more vigorously-growing reef-species. In addition there 
is the increasing importance of the nullipores on increase of depth, and Polytrema and other 
Foraminifera also, with Mollusca and other forms doubtless assist. Perhaps indeed all these 
are unnecessary, but their enumeration serves to point out their possible economic position 
in the formation of the reef. 
The next stage is dependent on the arrival of the larvae of the reef-building corals. 
Some fix themselves, and their resulting colonies soon commence to struggle with the 
possessors of the ground for supremacy. Their arrival is but slow, and at first they are 
probably spread out over the surface of the whole reef. As the shoal grows up oceanic 
and tidal currents over it become more definite. Its edges are more bathed than its central 
part and more oxygen, carbonic acid and food are carried to them. As a result the rims 
in particular soon send patches of reef up to the surface, to give rise finally to the perfect 
atoll through a series of changes, such as are sketched in my account of North Mahlos. 
The depth, to which the shoal would be raised before the reef-corals obtained sway, 
would naturally to some degree vary in different regions with their diverse conditions, and 
on this in the first place would depend the depth of the subsequent lagoon. It is not 
until the rim becomes moderately perfect that the latter begins to be hollowed out by 
solution, and until then its depth in the centre depends on that of the original shoal. In 
this case Tiladumati-Miladumadulu and Mahlos might be expected to show these depths, 
ie. 25 and 26 fathoms, while the atolls to the south demonstrate the increase of depth as 
the rim perfects itself. In this connection stress must only be laid on banks of considerable 
size, small ones having from the first more perfect reefs. The wave and current actions 
must be much less obstructed by small reefs, and hence there would be some considerable 
circulation of water over every part of them. They would then have been more covered 
over with reef-corals, and would accordingly, when they grew up, have shallower lagoons. 
The very smallest would have a solid, flat surface-reef with no lagoon at all. The larger 
atolls of this class probably include Goifurfehendu 23 fathoms, Rasdu 21 fathoms, Wattaru 
1 Vide note on p. 168. 
