168 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



hour, for four thousand seven hundred kilometres, and has a maximum 

 depth of more than four kilometres. 



Mention may also be made in this connection of the fact that the 

 Atlantic basin between West Africa and Brazil contains no materials of 

 direct land origin except near the continental shores. The deep sea 

 bottom is covered elsewhere with red clay and organic (Globigerina) 

 ooze.^ 



As to the possibility of Amazonian sources, the question is one of the 

 shore cuiTents and winds. But the currents along the northern coast 

 of Brazil set westward and northward, and unless there are in-shore 

 return currents, the sands brought down by the Amazonas cannot travel 

 southeastward. Besides, the methods of discharge of the streams north 

 of Cape Sao Eoque (all of them bend northwestward and follow the 

 coast) indicate that the sands of the coast are moving northward rather 

 than southward. 



The accompanying map showing the relief of the sea-floor out to the 

 100-fathom line has been constructed by drawing in contours from the 

 data on the hydrographic maps of the northeast coast of Brazil. This 

 map shows that the continental margin lies from 25 to 35 miles off" the 

 present shore. Over this shelf the water is rather uniform in depth. 

 The clean-cut shoulder about Cape St. Roque, where the eastern equa- 

 torial currents strikes it, and the gradual outward slope of this shoulder 

 toward the north, seem to suggest that the north-flowing current sweeps 

 in that direction the materials cut from the shoi-es. 



The fact is, that in the main the sands of the coast are of local origin. 

 They have simply been cut from the headlands and thrown back into 

 embayments, until the embayments were filled up, after which the en- 

 croaching sea has attacked these sands themselves and thrown them 

 upon the beaches, whence, when dry, they are swept up inland by the 

 on-shore winds that blow here the year round. The corallines, reef-build- 

 ing corals, and other lime-secreting organisms have also contributed enor- 

 mously to the recent sands of the coast, while the streams have all 

 brought down more or less sand from the land. An examination of the 

 sands made in June, July, and August, 1899, bears out this theory in 

 every detail. Along shores having corals reefs, the beach sands are cal- 

 careous ; where the coast rocks ai-e granites, gneisses, or schists, the sands 

 are made of the minerals composing those rocks. The sands of the beach 

 opposite the island of Santo Aleixo are different from the sands found 

 anywhere else on the coast, but the rocks of Santo Aleixo are different 



^ Challenger Reports. Deep-Sea Deposits. Chapter I. London, 1891. 



