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 currents 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 Sáo Roque (all of them bend northwestward and follow the 
coast) indicate that the sands of the coast are moving northward rather 
than south ward. 
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 shores. 
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 are 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 
1 Challenger Reports. Deep-Sea Deposits. Chapter I. London, 1801. 
