en produced by the subsidence of the land;
they were originally fringing reefs, having been attached to the
coastline of the country or islands. As the land sank, the insects went
on building one generation above another; but they can only work in a
certain depth of water--below which they die; thus a wall has been built
up on the foundations formed by the original workers, who constructed a
fringing reef. After a time, the last architects have died, storms have
thrown up pieces of coral shells and other debris on the top of the
wall, birds have brought seeds of plants, the ocean has washed cocoanuts
and other palm seeds on to the top: thus vegetation has been commenced,
and finally groves of trees and shrubs have grown up.

The barrier reefs have been formed in the same way. Where no vegetation
appears, the has probably sunk as rapidly as the creatures have built,
and the sea has continued to wash over it. Other groups have been
formed by the violent elevation of the land when the barrier reef has
been broken into and wide gaps have appeared.

The last island we visited, surrounded by high cliffs, must have been
formed by the sudden upheaval of the earth beneath it, so that the whole
mass of coral was lifted above water. Such has been the origin of a
considerable number of islands. The most beautiful and picturesque,
like Tahiti and others in that group, owe their present shape to the
subsidence to the earth, they being merely the summits of mountain
ranges, probably of some vast continent, of which the lower land has
been submerged. The gaps or openings in the encircling reefs are always
found opposite to a river or stream. The coral insect can only build in
pure salt water; the fresh water running out from the river has,
therefore, prevented its upward progress; thus a gap in the wall has
been formed serving as a safe entrance to the inner lagoon. Knowing
these facts, it was easy to decide to which class the islands and reefs
we passed belonged. There was always, therefore, matter of interest
before us.

Volcanic action has been the agent of many of the islands to the
westward, where several still active volcanoes exist. Many of those in
that direction are clothed with the richest vegetation. They are
inhabited by dark-skinned races; still the most savage among those of
the Pacific, such as the New Hebrides, Santa Cruz, Solomon Islands, and
New Ireland, to the eastward of New Guinea. They produce the f