32 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
not. But no careful study has ever been made of the shells in these 
beds and of their relations to the living shells of the coast, and until 
such a study is made the age of the shell beds cannot be considered ag 
determined. It has always been supposed, too, that the stone reefs of 
the coast were recent, but without a comprehensive study of their fossils 
and of the living fauna of the region it cannot be said positively whether 
they are recent or Pleistocene or some of them even of Pliocene age. 
For this question of the age of the later deposits along the coast is 
necessarily closely connected with the question of the ages of both the 
stone and coral reefs. If the stone reefs and raised beaches are late Ter- 
tiary, then the coral reefs are also Tertiary as well as recent, for the 
raised beaches at São Thomé, Porto Santo, and about Caravellas contain 
fragments of reef-building corals. In any case the later deposits along 
the coast are usually shut in the drowned river mouths and lakes, and 
in the old choked up embayments described in Chapter V. of this report. 
The stone reefs belong with these later deposits. 
Conclusions regarding the geology of the coast. — The interiors of all 
the states along the coast between Espirito Santo and Rio Grande do 
Norte are of old crystalline rocks. Against these old rocks rests a strip of 
sedimentary beds that varies considerably in width, and is even entirely 
wanting at several points. At the base of the sedimentary series appear 
to be isolated Cretaceous basins (and possibly even older ones) over- 
lapped by the more widespread Tertiary beds. 
The sedimentary rocks of the Bahia basin hitherto regarded as Creta- 
ceous appear to embrace more than one terrane. The oldest of these 
beds are Cretaceous (or possibly even Jurassic), and above these are 
probably Eocene beds, which are in turn overlain by later ones probably 
of Pliocene age. The separation of these several terranes cannot be 
made without more detailed stratigraphic work. South of Bahia as far 
as Abrolhos, and north of Bahia, at least as far as Natal, we seem to have 
here and there in the coastal sediments a stratigraphic problem very 
similar to that of the Bahia basin, but with less data with which to 
solve it: there may be two or more undefined terranes with Cretaceous 
below and Eocene Tertiary above, or, if there is but one terrane, we 
have in Brazil a faunal combination unlike any known in other parts of 
the world. 
The brilliant colors of the coastal sediments have been produced by 
weathering ; they affect beds of different ages and to varying depths, and 
cannot, therefore, be used to determine the ages of the rocks. At many 
places these beds are somewhat folded, but the weathering has so affected 
