lagoon-island generally supports many separate small islands, the word
"island," applied to the whole, is often the cause of confusion; hence I
have invariably used in this volume the term "atoll," which is the name
given to these circular groups of coral-islets by their inhabitants in the
Indian Ocean, and is synonymous with "lagoon-island."

(PLATE: UNTITLED WOODCUT, REEF AT BOLABOLA ISLAND.)

Barrier-reefs, when encircling small islands, have been comparatively
little noticed by voyagers; but they well deserve attention. In their
structure they are little less marvellous than atolls, and they give a
singular and most picturesque character to the scenery of the islands they
surround. In the accompanying sketch, taken from the "Voyage of the
'Coquille'," the reef is seen from within, from one of the high peaks of
the island of Bolabola. (I have taken the liberty of simplifying the
foreground, and leaving out a mountainous island in the far distance.)
Here, as in Whitsunday Island, the whole of that part of the reef which is
visible is converted into land. This is a circumstance of rare occurrence;
more usually a snow-white line of great breakers, with here and there an
islet crowned by cocoa-nut trees, separates the smooth waters of the
lagoon-like channel from the waves of the open sea. The barrier-reefs of
Australia and of New Caledonia, owing to their enormous dimensions, have
excited much attention: in structure and form they resemble those
encircling many of the smaller islands in the Pacific Ocean.

With respect to fringing, or shore-reefs, there is little in their
structure which needs explanation; and their name expresses their
comparatively small extension. They differ from barrier-reefs in not lying
so far from the shore, and in not having within a broad channel of deep
water. Reefs also occur around submerged banks of sediment and of worn-down