At High Water The Waves
Break Over It; At Low Water Its Summit Is Left Dry, And It
Might Then Be Mistaken For A Breakwater Erected By Cyclopean
Workmen.
On this coast the currents of the sea tend
to throw up in front of the land, long spits and bars of
loose sand, and on one of these, part of the town of Pernambuco
stands.
In former times a long spit of this nature
seems to have become consolidated by the percolation of
calcareous matter, and afterwards to have been gradually
upheaved; the outer and loose parts during this process having
been worn away by the action of the sea, and the solid
nucleus left as we now see it. Although night and day the
waves of the open Atlantic, turbid with sediment, are
driven against the steep outside edges of this wall of stone,
yet the oldest pilots know of no tradition of any change in its
appearance. This durability is much the most curious fact
in its history: it is due to a tough layer, a few inches thick,
of calcareous matter, wholly formed by the successive
growth and death of the small shells of Serpulae, together
with some few barnacles and nulliporae. These nulliporae,
which are hard, very simply-organized sea-plants, play an
analogous and important part in protecting the upper surfaces
of coral-reefs, behind and within the breakers, where
the true corals, during the outward growth of the mass,
become killed by exposure to the sun and air.
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