146 
THEORY OF THE FORMATION 
Ch. V. 
their origin to the disseverment of a single large 
atoll. 1 
Irregularly -formed Atolls . — In the Marshall group, 
Musquillo atoll consists of two loops united by a single 
point ; and Menchicoff atoll is formed of three loops, 
two of which (as may be seen in fig. 3, Plate II.) are 
connected by a mere ribbon-shaped reef; the three 
together being 60 miles in length. In the Gilbert group 
some of the atolls have narrow reefs like spurs, pro- 
jecting from them. Linear and straight, or crescent- 
formed reefs with their extremities more or less curled 
inwards, may sometimes be found standing by them- 
selves in the open ocean. All these irregular forms 
would naturally follow from continued subsidence, 
combined with the upward growth of reefs fronting 
one side alone of a high island, the reefs on the op- 
posite side having perished or never having existed. 
Submerged and Dead Reefs . — In the second section 
of the first chapter, I have shown that there some- 
times exist in the neighbourhood of atolls, deeply 
submerged banks with level surfaces ; that there are 
others, less deeply but yet wholly submerged, having 
all the characters of a perfect atoll, but consisting 
1 The same remark is, perhaps, applicable to the islands of Ollap, 
Fanadik, and Tamatam in the Caroline Archipelago, of which charts 
are given in the atlas of Duperrey’s voyage ; a line drawn through 
the linear reefs and lagoons of these three islands form a semicircle. 
Consult also the atlas of LutkAs voyage ; and for the Marshall group 
that of Kotzebue ; for the Gilbert group (which is referred to in the 
ensuing paragraph) consult the atlas of Duperrey's voyage. Most of 
the points here referred to may, however, be seen in Krusenslern’s 
general Atlas of the Pacific. 
