bulletin: museum of comparative zoology. 



II. 



Sketch of the Geology of the Coast in its Relations to the 

 Stone and Coral Reefs. 



Pre-Cretaceous 8 



The Cretaceous 9 



What is the age of the Bahia beds? 9 

 Conclusion regarding tlie Bahia 



beds 11 



The age of the other coast sedi- 

 ments 13 



PAGE 



The relation of color to age ... 18 

 The Tertiary beds of the Ania- 



zonas 25 



The later Tertiary deposits ... 27 



Recent deposits 31 



Conclusions regarding the geol- 

 ogy of the coast 32 



The discussion of the stone reefs of Brazil is both a geological and a 

 geographical one. It is therefore necessary to get our geological orien- 

 tation, — to have some idea of the general geological history of the 

 region discussed, before treating of the reefs themselves. This is essen- 

 tial, because the reefs are of late geological origin, and it is necessary 

 to understand the geological history of the coast in order to see where 

 the reefs came into that history. It is also the more necessary on ac- 

 count of many statements in the present paper that do not agree with 

 earlier publications regarding the geology of the region here treated. 



Pre- Cretaceous. — The principal feature of the coast geology with 

 which we have to deal is a series of mechanical and organic sediments 

 forming a plateau along nearly the whole of the coast from the northern 

 part of the State of Rio Grande do Norte to the State of Espirito Santo, 

 — a distance of nearly two thousand kilometres. Over most of this dis- 

 tance these sediments rest upon crystalline rocks, — in some places 

 granites, in other places gneisses, in others schists. These old ci-ystalline 

 rocks are cut here and there by eruptive dikes of later age. The age 

 of the old underlying beds is not known, but the schist series looks very 

 like the Algonkian of Van Hise, At one place — the Serra of Itabaiana, 

 in the State of Sergipe — there are older sediments between the crys- 

 talline rocks and the later sediments known to be of Cretaceous age. 

 Xo fossils have been found in these lower beds, but from their position 

 below the Cretaceous beds they have been provisionall}- assigned to the 



