1 879.] 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 traveling 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, Siderastrcca Stella ta 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 



