THE FORMATION OF THE MALDIVES AND LACCADIVES, 181 

of other banks, and also if there is—instead of deep sea—shallow water, a ridge in fact 
on either side. The consideration of the current factor is, I believe, a most important one. 
It acts on coral growth in two ways, advantageously by constantly bringing fresh water 
and disadvantageously by sweeping sediment over the corals, by preventing fixation of the 
larvae, and, when strong, by stunting and even breaking the corals. On a bank at 25 to 
30 fathoms patches all over the surface would commence to grow up, wherever the conditions 
might happen to be especially advantageous. A fairly definite rim might early be expected 
to show itself, but together with its growth there would be an increase of current over 
the bank. If the bank be small or isolated there might not be a sufficient increase to 
affect the growth of the rim as a whole, though some parts would possibly from the first 
be lower and, serving as outfalls for the water, form the passages. In this way atolls such 
as Addu and Goifurfehendu and others have probably been formed. 
On the other hand, in atolls of the next size some part of the rim might be more 
perfect from the commencement, and in the central banks of the Maldives it would naturally 
be that on the east side of the east line of reefs and on the west of the west line, these 
sides being more exposed to the sea and hence to more favourable conditions. This is at 
once illustrated in the more perfect reefs of these two sides in Felidu, Mulaku, North and 
South Nilandu and Fadifolu atolls. Lastly over the largest banks of the central plateau 
the currents, both oceanic and tidal, must be from their position and size much stronger, 
and probably from the first in Mahlos and Tiladumati-Miladumadulu the corals could only 
build up patches of reef on the rim. The condition would remain open and shoals would 
grow up anywhere on the centre of the bank. Until the wall of the bank became fairly 
perfect each patch would behave as an isolated reef in the ocean, and by spreading out 
on all sides and becoming hollowed in the centre form an atoll. The rate at which this 
might occur would, as compared with an isolated reef in the ocean, be enormously increased 
owing to the shallow depth of the foundations on which the corals would spread out to 
almost any extent. 
Of other atolls in the Maldives Kolumadulu and Haddumati are exposed both east and 
west to the full action of the sea, and are less enclosed than others by their neighbours. 
They only differ from Suvadiva in their smaller size, but the latter is still less contiguous 
to its fellows. The encircling reefs of these banks are fairly perfect, though they are broken 
by numerous passages into their lagoons. A study of their lines of circumscribing reefs 
shows that the conditions are not so simple as at first sight might appear, since they have 
a line of shallow pools along their centres. Either the rim grew up double—the conditions 
inside such large banks being supposed to be the same as outside—or the reefs were formed 
by the fusion of a series of faro. The first condition is conceivable and partially accounts 
for the outgrowth of the ring-reefs of Mahlos, but such growth only continues while the 
passages into the bank are numerous. Between these pools the encircling reef narrows 
somewhat, and its close examination shows that it was rather formed by the fusion together 
of an enormous number of little patches. For this fusion to have taken place on some 
banks, while the patches are still separate in so many others, the rim as a whole must 
have grown considerably and the passages been shallow, but then there is the elevation of 
the group, which with shallow channels may have been of great assistance. It is not 
necessary, however, that each passage should have had at least its present depth of water 
at all times; many are being filled up by coral growth, and it is more than probable 
