BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
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Introduction. 
THERE is no more striking geologic phenomenon along the eastern 
shores of South America than the stone reefs of Brazil. 
These reefs are supposed by many persons to be of coral, and this error 
has been propagated by writers of books of travels and by works on the 
navigation of the south Atlantic. There are several reasons for this 
error : coral reefs border many tropical coasts in a similar manner ; there 
are extensive coral reefs on the coast of Brazil ; the stone reefs of Brazil 
are unique, or rather they are found nowhere else in the world except 
on а very limited scale; seen from a vessel sailing along the coast or 
even near at hand, the stone reefs are scarcely distinguishable from 
coral reefs even by an expert; and, finally, the sandstone reefs are 
generally covered with calcareous growths common to coral reefs, The 
only thing that is especially characteristic of the form of stone reefs 
is their straightness, and this is not always apparent to one looking at 
them either from the shore or from the ocean. In Brazil the only men 
who really seem to know the difference between the two kinds of reefs 
are the lime-burners who make lime of the corals, and a few of the 
masters of barcacas, or sugar boats. Among these men distinction 
is made between the coral rock, which they know ав pedra de cal (lime 
rock), or as cabeça de carneiro (sheep’s head, referring to Porites and 
other solid heads), and the sandstone which they call pedra de encantaría ; 
that is, stone used for window and door sills and facings, as the. reef 
rocks have been used from the earliest times. 
Tn a sense the sandstone reefs are local, but the forces and agencies 
that have formed them have been in operation along the entire coast, 
from near Maranháo to southern Bahia, while local conditions have pre- 
vented their formation at some places, or have favored their preservation 
or destruction at others. 
The ports and towns behind the stone reefs owe everything to them. 
Without these reefs there would be no Pernambuco, no Rio Grande do 
Norte, no Porto Seguro, no Santa Cruz, to say nothing of the minor 
ports like Rio Formoso, Serinhaem, Suápe, Traição, Mamanguape, and 
