of the peak.

L', lagoon of the atoll.

The vertical scale is considerably exaggerated as compared with the
horizontal scale.]

The remarkable characters of barrier reefs and atolls, their isolated
position in the midst of the great oceans the seemingly unfathomable
depths from which they rise their peaceful and shallow lagoons and inner
channels, their narrow strips of land covered with coco-nut palms and
other vegetation, and rising but a few feet above the level of the
ocean, naturally attracted the attention of the earlier navigators, who
formed sundry speculations as to their origin. The poet-naturalist, A.
von Chamisso, was the first to propound a definite theory of the origin
of atolls and encircling reefs, attributing their peculiar features to
the natural growth of corals and the action of the waves. He pointed out
that the larger and more massive species of corals flourish best on the
outer sides of a reef, whilst the more interior corals are killed or
stunted in growth by the accumulation of coral and other debris. Thus
the outer edge of a submerged reef is the first to reach the surface,
and a ring of land being formed by materials piled up by the waves, an
atoll with a central lagoon is produced. Chamisso's theory necessarily
assumed the existence of a great number of submerged banks reaching
nearly, but not quite, to the surface of the sea in the Pacific and
Indian oceans, and the difficulty of accounting for the existence of so
many of these led C. Darwin to reject his views and bring forward an
explanation which may be called the theory of _subsidence_. Starting
from the well-known premise that reef-building species of corals do not
flourish in a greater depth of water than 20 fathoms, Darwin argued that
all coral islands must have a rocky base, and that it was inconceivable
that, in such large tracts of sea as occur in the Pacific and Indian
oceans, there should be a vast number of submarine peaks or banks all
rising to within 20 or 30 fathoms of the surface and none emerging above
it. But on the supposition that the atolls and encircling reefs were
formed round land which was undergoing a slow movement of subsidence,
their structure could easily be explained. Take the case of an island
consisting of a single high peak. At first the coral growth would form a
fringing reef clinging to its shores. As the island slowly subsided into
the ocean the upward growth of coral would keep the outer rim of