NORTH MAHLOS BANK. 171 
continuous reef having extended on any side. Indeed no one, who dispassionately considers 
the fact that the passages are in most cases as deep or deeper than the interior of the 
bank in their vicinity, can fail to see in this the strongest possible evidence against any 
such view. Hach large reef on the bank is a separate entity that has grown up and 
pursued its history by itself, influenced it is true by the reefs in its vicinity but never 
directly connected with them. It is only now that the bank is at all approaching the 
condition of the perfect atoll. Having seen how small faro may be formed from their 
earliest beginnings, we now see in North Mahlos the further fortune of such atolls, their 
joining together where possible to form long linear reefs with the loss perhaps of the whole 
inner part of their own reefs. We find too in Mahlos different physical conditions, and 
the consideration of its reefs in different parts shows how they are affected, and points 
to some of the factors that must have been of importance in forming the lagoons of our 
perfect atolls. The bank, on which these reefs have been built up, was at some former 
time a plateau at a depth apparently of not more than 30 fathoms, and there must have 
been on its outer edge a special tendency of growth to have formed its existing series 
of reefs. When I say that it was a plateau, I am perhaps neglecting the “jungle of 
reefs” that is found in its centre. There is here a distinct decrease in the general depth 
of our bank, which from side to side in this situation would appear to have been dome- 
shaped. This “jungle” is, so far as I am aware, without parallel on any other coral 
bank of the Pacific or Indian Oceans, and is, I consider, entirely a local feature, complicating 
our problem. The history of the bank as a whole has been further confused by the 
elevation of some land, the wash from which must have profoundly affected the reefs 
round it and retarded their formation and growth. That any rocky land has been formed 
save by this change of level is so far as I can see impossible, but many islets in the 
centre of the group have indubitably been washed up as sand-banks. With other larger sandy 
islands the origin is less clear, but it is singular that they all show erosion of their shores 
and some an extraordinary loss. With the growing up of the rim the eddies and currents 
must be constantly profoundly changed, and it is to this that some islands owed their 
origin as perhaps they now owe their erosion. The differences between the east and west 
sides of the bank must be mainly due to the difference in force of the monsoons on the 
two sides. In the first place the stronger and more regular wash on the west as compared 
with the east side would tend to make its reefs larger and more defined. All these reefs 
had land, where rock masses are now found. This was much more rapidly washed away 
on the west than the east side. And, lastly, whereas the reef-platform is very narrow on 
the east side, it has on the west the regular slope off oceanic reefs. However interesting 
these considerations relating to the land may be, they nevertheless do not affect the general 
conclusions as to the growth and formation of atolls, of the which for further evidence 
I must refer to the Appendix. 
