comparing them with Keeling atoll. The Maldiva atolls and the Great Chagos
Bank differ in so many respects, that I shall devote to them, besides
occasional references, a third section of this chapter. Keeling atoll may
be considered as of moderate dimensions and of regular form. Of the
thirty-two islands surveyed by Captain Beechey in the Low Archipelago, the
longest was found to be thirty miles, and the shortest less than a mile;
but Vliegen atoll, situated in another part of the same group, appears to
be sixty miles long and twenty broad. Most of the atolls in this group are
of an elongated form; thus Bow Island is thirty miles in length, and on an
average only six in width (See Figure 4, Plate I.), and Clermont Tonnere
has nearly the same proportions. In the Marshall Archipelago (the Ralick
and Radack group of Kotzebue) several of the atolls are more than thirty
miles in length, and Rimsky Korsacoff is fifty-four long, and twenty wide,
at the broadest part of its irregular outline. Most of the atolls in the
Maldiva Archipelago are of great size, one of them (which, however, bears a
double name) measured in a medial and slightly curved line, is no less than
eighty-eight geographical miles long, its greatest width being under
twenty, and its least only nine and a half miles. Some atolls have spurs
projecting from them; and in the Marshall group there are atolls united
together by linear reefs, for instance Menchikoff Island (See Figure 3,
Plate II.), which is sixty miles in length, and consists of three loops
tied together. In far the greater number of cases an atoll consists of a
simple elongated ring, with its outline moderately regular.

The average width of the annular wreath may be taken as about a quarter of
a mile. Captain Beechey (Beechey's "Voyage to the Pacific and Beering's
Straits," chapter viii.) says that in the atolls of the Low Archipelago it
exceeded in no instance half a mile. The description given of the
structure and proportional dimensions of the reef and islets of Keeling
atoll, appears to apply perfectly to nearly all the atolls in the Pacific