Ch. in. 
FRINGING REEFS. 
77 
The coast of Brazil is in many parts fringed by reefs. 
Of these, some are not of coral formation ; for instance, 
those near Bahia and in front of Pernambuco ; but a 
few miles south of this latter city, the reef follows 1 every 
turn of the shore so closely, that I can hardly doubt it 
is of coral. It runs at the distance of three-quarters 
of a mile from the land, and within it the depth is 
from ten to fifteen feet. I was assured by an intelli- 
gent pilot, that at Ports Frances and Maceio, the outer 
part of the reef consists of living coral, and the inner 
of a white stone full of large irregular cavities com- 
municating with the sea . 2 The bottom of the sea off 
the coast of Brazil shoals gradually to between thirty 
and forty fathoms, at the distance of between nine and 
ten leagues from the land. 
From the description now given, we may conclude 
that the dimensions and structure of fringing-reefs 
depend entirely on the greater or less inclination of the 
submarine slope, conjoined with the fact, that reef- 
building polypifers can exist only at limited depths. 
It follows from this, that where the sea is very shallow, 
as in the Persian Gulf and in parts of the East Indian 
Archipelago, the reefs lose their fringing character, 
1 Baron Roussin’s Pilote du Brdsil, and the accompanying hydro- 
graphical memoir. See also the supplement to this volume on a Bar 
of Sandstone off Pernambuco. 
2 [Rathbun (Amer. Nat., xiii. 539-551) describes a reef on the 
Brazilian coast. The lower part of the reef consists of true corals, 
the upper of nullipores and annelid tubes. The reef has a loose 
structure near the surface, compact below. The coral fragments cover- 
ing the channel within the reef ‘ form beds of considerable thicknes3 
in places, often more or less consolidated.’] 
7 
