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BRANNER: THE STONE REEFS OF BRAZIL. 181 
We have no means of determining the age of the rocks of these islands, 
but the freshness of the lavas and the rapidity with which the shores are 
being eroded by wave action lead us to infer that they are new." 
The position of these eruptive islands affords a basis for the theory 
that either at the time of the extrusion of the rocks that form the group, 
or at some subsequent eruption, large quantities of carbon dioxide may 
have escaped into the sea. The South Atlantic current at this latitude 
flows westward, but during eight months of the year (October to May, 
inclusive) the northeast trade winds shift it somewhat toward the south, 
so that during those months the oceanic currents that pass Fernando 
flow toward Cape St. Roque, and thence pass southward along the east 
coast of Brazil, past Rio Grande do Norte, Pernambuco, Rio Formoso, 
Bahia, etc. These currents would have thrown the carbon dioxide, had 
they contained it, against the shores along the northeast coast of Brazil 
from Cape St. Roque southward. 
But if submarine discharges of carbon dioxide have taken place, and if 
beach sands have been hardened as here suggested, we may reasonably 
expect to find beach sands similarly consolidated in other parts of the 
world. There are indeed many cases known of the hardening of recent 
beach sands. In only two instances, however, do they appear to have 
been hardened by carbon dioxide escaping from submarine vents: these 
are in the Straits of Messina between Sicily and Italy, and on the shores 
of the Red Sea.2 In both of these cases the consolidation has taken 
place in the vicinity of voleanic activity. 
We seem warranted in the conclusions that carbon dioxide of volcanic 
origin is discharged beneath the sea; that it is competent to cause the 
hardening of beach sands; and that the existence of a volcanic island 
off the northeast coast of Brazil makes it possible that such discharges 
may have taken place there. But inasmuch as the lithification of the 
coast sands of the region is in various stages of development, and as 
1 Northwest of Fernando de Noronha and eighty miles away is another small 
island known as the Rocas. This island is about two miles long (east-west) by one 
and three-fourths miles wide, and was until lately uninhabited. I have never 
visited the place, but from information kindly furnished me by Commandante 
Huet Bacellar, of the Brazilian navy, who has visited the place, I conclude that 
the rocks there are corals. But whether the corals have igneous rocks beneath 
them, I have been unable to learn. Except some dunes on the southwest corner, 
it is all covered by water at high tide. On the Rocas, see р. 226-227 of this report. 
2 Hawkshaw, Quar. Journ. Geol. Soc., 1879, XXXV., p. 242. 
Suess says history mentions many eruptions on the Red Sea. Face de la Terre, 
p. 478, note. 
