BRANNER: THE STONE REEFS OF BRAZIL. 261 
Rio Formoso, Maceio, and Tamandaré may be taken as the type of this kind 
of geographic relations of the reefs. The reefs in such places are usually 
long and slender, and it is believed that they are younger than the large 
reefs, These forms are so constant that one profile can be substituted 
for another without modification of any of the essential features. In the 
cases of the largest reefs, such as those of Cape São Roque reefs, the 
Parcel das Paredes and the Abrolhos reefs, the adjoining coasts are low, 
and the coral reefs are probably older and thicker than they are off the 
steep shores of the coast of Pernambuco and Alagóas. 
In at least one instance it seems probable that the coral reef (that at 
Parahyba do Norte) has taken possession of and is now growing upon a 
submerged stone reef. Briefly stated, the reasons for this opinion are: — 
„1. A deep well sunk at Cabedello inside the reef penetrated only the 
soft coastal sands, 
II. The reef lies across the ancient mouth of the Rio Parahyba do 
Norte, —the position in which the stone reefs of the coast are usually 
formed. 
The coral reef could live in its present position, however, only after 
the formation of the Ponta da Matta spit, which turned the river waters 
away from the reef. The coral of the Parahyba reef is probably less 
than five metres in thickness. 
The actual thickness of the reefs can, in my opinion, be ascertained 
with absolute certainty in but one way, and that is, by boring into the 
reefs at a large number of places. Some idea of their thickness can be 
had, however, by working out the geological and geographical history of 
the coast. The first method it has not been convenient to employ ; the 
Second one has been made use of in the present paper in so far as it has 
been possible to make out the coast history. We must conclude, there- 
fore, that the coral reefs of the Brazilian coast probably nowhere exceed 
a thickness of one hundred metres. Most of them are much thinner 
and do not exceed fifty metres. The greater part of them are even 
thinner than this. 
The age of the coral reefs. — The existing coral reefs are necessaril y de- 
scended from the ancient ones. But the geologic and geographic history 
of the Brazilian coast cannot be traced with much precision further back 
than Tertiary times. 
Magnesian limestones and dolomites found among the Cretaceous 
rocks of Sergipe and in the Cretaceous (or Tertiary T) rocks of Pernam- 
buco, and Rio Grande do Norte show that coral reefs existed* on this 
Coast in Cretaceous times and the present reefs must be descended from 
