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-organised 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. These
insignificant organic beings, especially the Serpulae, have done
good service to the people of Pernambuco; for without their
protective aid the bar of sandstone would inevitably have been long
ago worn away and without the bar, there would have been no
harbour.
On the 19th of August we finally left the shores of Brazil. I thank
God, I shall never again visit a slave-country. To this day, if I
hear a distant scream, it recalls with painful vividness my
feelings, when passing a house near Pernambuco, I heard the most
pitiable moans, and could not but suspect that some poor slave was
being tortured, yet knew that I was as powerless as a child even to
remonstrate.
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