1879.] Brazilian Corals and Coral Reefs. 541 
Having thus briefly defined our present knowledge of Brazilian 
corals and coral reefs, let us proceed to study them more in detail, 
as they appear to one ie through the regions in which 
they are contained. 
Rocky shores, although usually of a tame character, are not 
uncommon in the coral region of Brazil, and they afford a proper 
footing for the growth of corals, both as scattered masses and in 
the form of reefs. The Bay of Bahia has quite a rich coral 
fauna, and presenting a varied shore enables us to study well the 
several littoral and shallow water species. As we enter the bay 
through its broad mouth, high cliffs of gneiss stand up before us 
on the right, but they soon give way to a low, and often nearly 
level shore of Cretaceous shales, sandstones and conglomerates, 
which, interspersed with beaches of sand, border almost the entire 
bay. Long stretches of rock lie under the influence of the tides, 
being entirely covered during flood, and exposed at low water. 
In addition to these, countless ledges exist everywhere off the 
shore, and being always submerged are better suited for coral life. 
In the many tide pools of the rocky surfaces, and just below 
the level of low tide, live in abundance two of the most common 
of the Brazilian corals, Siderastrea stellata and Favia gravida. 
These two species are almost always associated together, and they 
range throughout the entire coral region above defined. The for- 
mer is, however, the more abundant, and attains the larger size; 
it is also the more hardy species, and at low tide may be exposed 
to a burning sun for an hour or more without sustaining injury. 
The size and shape of these coral masses, as well as the general 
structure of their cells, often vary greatly, according to the kind 
of rock on which they grow. 
If the shore be formed of shales, presenting a level surface but 
affording only an insecure attachment, the corallum will spread 
outwards rather than upwards, giving rise to a thin flattened mass 
which may be over a foot and a half across and less than an inch 
thick. A smooth sandstone surface gives a firmer foundation, 
and permits, as it were, a thicker growth, although the tendency 
is still toward lateral spreading. Shores of gneiss and conglom- 
erate are, however, generally rough and jagged, pierced with 
irregular holes and beset with multitudes of rounded or angular 
projections, On such a surface the growth of flat and level cor- __ 
alla is impossible ; they tend to rise in hemispherical or globular 
