the lagoon-channels of most barrier-reefs, and which stand either isolated,
or are attached to the shores of the reef or land. At Peros Banhos none of
the lagoon-reefs rise to the surface of the water; a few of them have
been introduced, and are marked by plain dotted circles. A few of the
deepest soundings are laid down within each reef; they are in fathoms, of
six English feet.

Figure 1.--VANIKORO, situated in the western part of the South Pacific;
taken from the survey by Captain D'Urville in the "Astrolabe;" the
soundings on the southern side of the island, namely, from thirty to forty
fathoms, are given from the voyage of the Chev. Dillon; the other soundings
are laid down from the survey by D'Urville; height of the summit of the
island is 3,032 feet. The principal small detached reefs within the
lagoon-channel have in this instance been represented. The southern shore
of the island is narrowly fringed by a reef: if the engraver had carried
this reef entirely round both islands, this figure would have served (by
leaving out in imagination the barrier-reef) as a good specimen of an
abruptly-sided island, surrounded by a reef of the fringing class.

Figure 2.--HOGOLEU, or ROUG, in the Caroline Archipelago; taken from the
"Atlas of the Voyage of the 'Astrolabe,'" compiled from the surveys of
Captains Duperrey and D'Urville; the depth of the immense lagoon-like space
within the reef is not known.

Figure 3.--RAIATEA, in the Society Archipelago; from the map given in the
quarto edition of "Cook's First Voyage;" it is probably not accurate.

Figure 4.--BOW, or HEYOU ATOLL (or lagoon-island), in the Low Archipelago,
from the survey by Captain Beechey, R.N.; the lagoon is choked up with
reefs, but the average greatest depth of about twenty fathoms, is given