Sect. II. 
ATOLLS. 
37 
to leeward as regards the trade-wind, are in most 
parts of the Pacific liable to be occasionally swept 
entirely away by gales, equalling hurricanes in vio- 
lence, which blow in the opposite direction. The 
absence of islets on the leeward side of atolls, or, 
when present, their lesser dimensions compared with 
those to windward, is a comparatively unimportant 
fact ; hut it is remarkable that in several instances 
the reef itself, although retaining its usual defined 
outline, does not rise to the surface by several fathoms 
on the leeward side. This is the case with the 
southern side of Peros Banhos (Plate I. fig. 9) in the 
Chagos group, with Mourileu atoll 1 in the Caroline 
Archipelago, and with the barrier reef (Plate I. fig. 8) 
of the Gambier Islands, where Captain Beecliey was 
first led to observe the peculiarity in question. At 
Peros Banhos the submerged part is nine miles in 
length, and lies at an average depth of about 
five fathoms ; its surface is nearly level, and consists 
of hard stone with a thin covering of loose sand. 
There is scarcely any living coral on it, even on the 
outer margin, as I have been particularly assured by 
Captain Moresby: itis,infact,awallof dead coral-rock, 
having the same width and transverse section with the 
reef in its ordinary state, of which it is a continuous 
portion. The living and perfect parts terminate 
abruptly, and abut on the submerged portions, in 
' Frederic Lutke’s Voyage autour du Monde, vol. ii. p. 291. See 
also his account of Namonouito, at pp. 97 and 105, and the chart of 
Oulleay in the Atlas. 
