180 J. STANLEY GARDINER. 
18 fathoms, Makunudu 19 fathoms, and Ihavandifolu 28 fathoms, besides some of those in 
the Laccadives. Toddu, Karidu, and Fua-Mulaku, being smaller, have not yet attained by 
secondary means, @.e. growth outwards and solution of central parts, the atoll condition, and 
their reefs being still crowned with land will have to be reduced to the bare reef before 
they can do so. 
This depth, about 26 fathoms, found in Tiladumati-Miladumadulu and Mahlos is the 
same also as occurs on many submerged banks. In the first place attention may be called 
to those in the Laccadives, as they have not yet begun to assume an atoll shape. Of 
these one is small and has only 6 fathoms of water, but the other three are much larger 
and have 23, 26 and 28 fathoms. Indirectly these banks too serve to give additional proof 
of the above theories. Being domed they cannot be submerged atolls. Considerable 
irregularity in depth strongly opposes the idea that they are still being cut down by the 
sea. Further they have apparently precipitous walls. If the encircling reefs of atolls do 
ever actually grow up directly from 40 to 50 fathoms, taking the depths of the lagoons 
of some, it is remarkable that these banks as yet show no signs of any such reefs. Turning 
to the shoals of the Pacific I may refer to those recently mentioned by Admiral Sir 
W. L. Wharton to the north of Fiji, five in number, with depths of 24 to 26 fathoms 
in their centres. The second largest of these, the Alexa bank, 18 by 9 miles, has a perfect 
rim 13 to 18 fathoms in depth. Speaker's and Pitt banks in the Chagos are also nearly 
comparable in size and have 24 and 22 fathoms. Many other similar shoals might be cited, 
but reference may be made rather to those which markedly differ. First Saya de Malha 
has a sounding of 65 on the centre but only 22 fathoms on the rim; yet the merest 
glance at the chart on p. 14 serves to show that it is in its foundations comparable rather 
to the great Maldive plateau than to. its several banks. Great Chagos, Tizard and Macclesfield 
all have over 45 fathoms. The first is of great size (see p. 17), and all three have the 
rim though largely submerged far more perfect than that, for instance, of Tiladumati- 
Miladumadulu. The larger the bank the more tendency there is for the rim to grow up 
from a greater depth, as more food would reach the sides before the centre. However, as 
already remarked, the formation of each reef must be considered by itself in view of the 
physical conditions of its region. These may be expected to profoundly modify it, and 
probably are largely responsible for the variations that occur. In the above I have only 
tried to sketch the conditions which have been affecting the formation of the reefs im the 
Maldives. I would not necessarily apply them to all reefs, though I believe that in their 
main principles they will be found to be true also of the greater number in the Pacific 
and Indian Oceans. 
I have already indicated under Mahlos the changes that take place to form an atoll, 
but a further reference is necessary to the enclosing or rim reefs. These may in the smaller 
banks almost grow up as such in the perfect state, more or less completely surrounding 
the lagoon. ‘The relative length of the reef roughly varies inversely as the size of the 
bank, and the amount of water which must pass over it directly. Further, the greater part 
of the current, oceanic or tidal, may be diverted on either side of a small bank, whereas 
a relatively much greater amount of water, conditions of depth, etc. being the same, must 
pass over the encircling reef of a larger bank. Such being obviously the case it is apparent 
that the outfalls for the water may be relatively very much less numerous and smaller 
from small than large banks. Again, the amount of current will increase with the contiguity 
