104 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
posed by him, and I know of no small atoll in which any such platform 
has been observed. 
Neither Dana nor Lendenfeld seem to take into account the mass of 
water which is poured into a lagoon, even if it has no boat passage, over 
the reef flat at low tide, to say nothing of the period during which the 
reef remains covered between low and high water times. 
A large atoll, like that of Ngele Levu, if it has been formed by 
subsidence, should be of greater depth. This has already been noticed 
by Admiral Wharton.t Ngele Levu is thirty-three miles round, grad- 
ually increasing in depth towards the western extremity from four to 
sixteen fathoms. It rises gradually from a ridge with a depth of about 
145 fathoms, and from a plateau of less than 400 fathoms in depth. 
There is no filling up of that lagoon; it is well scoured, and a strong 
current is constantly deepening the entrance and outlets at the western 
end, to say nothing of the mass of water which finds its way out over 
the reef flat. The lagoon of an atoll is often referred to by writers on 
coral reefs as a sort of stagnant pool, which must of necessity be grad- 
ually filling. Such is certainly not the case in the atolls with which I 
am acquainted, and it is the exception. If any one will take the trouble 
to examine the hydrographic charts of the coral reef regions, both in the 
Pacific and the Atlantic, they will find it to be the exception when the 
atoll of a lagoon is really impounded, or that of a barrier reef is shut 
out from a most active circulation carried on by the breakers rolling 
over the rim of the one and the barrier of the other into the enclosed 
lagoon. In Fiji, the only atolls which are enclosed and surrounded by 
a reef allowing no circulation or access to the sea are small, and play 
no part in the physiognomy of the reefs of the group, and I know of 
no barrier reef in Fiji the lagoon of which is not well threshed by 
the breakers, 
An examination of the charts accompanying this report will show on 
the rim of the larger atolls, both to windward and leeward, moderate 
depths, from one to three fathoms or less at innumerable places, forming 
a regular sieve of passages through which the breakers force their way. 
An examination of the charts will show the same results as regards the 
circulation across the barrier reefs of Fiji. Finally, we should re- 
member that at high tide even fringing reefs are washed in every part 
and scoured, and that, while at low tide a certain amount of stagnation 
in pools may occur, it is only temporary, and not the natural state of 
things. 
1 Nature, May 22, 1890, p. 81. 
