32 bulletin: museum of compakative 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 as 

 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 Sao Thome, 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 Kio Grande da 

 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 regai'ded as Creta- 

 ceous appear to embrace more than one terrane. The oldest of these 

 beds are Cretaceous (or possibly even Jurassic), and above these arc 

 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 tlie ages of the rocks. At many 

 places these beds are somewhat folded, but the weathering has so affected 



