BRANNER: THE STONE REEFS OF BRAZIL. 245 
south of Pioca, and south of the bay they continue again as three or four 
overlapping reefs. 
Just above the mouth of Rio Santo Antonio Mirim that stream passes 
over a submerged reef. This reef was under water when it was passed, 
but judging from its jagged uneven surface over which we had to wade 
it is thought to be a coral reef. Both ends of the reef are covered by 
sand spits. 
At Riacho Doce, sonth latitude 9° 36’, and from there to Garga Torta 
are several exposures of coral reefs on shore in addition to the large reefs 
outside, 
Ав pointed ont in the geological introduction, the rocks exposed along 
this part of the coast are probably of Tertiary age, beginning with heavy 
basal conglomerates containing large boulders of granite. Resting upon 
these conglomerates is a series of sandstones and bituminous shales 
wrinkled and faulted. These sedimentary beds have been cut off by 
the waves, and on top of the eroded surface have grown the coral reefs. 
In places the corals cover the granite blocks washed out of the basal 
conglomerates. At one place for a distance of thirty metres there is a 
sandstone reef on top of a coral reef which. in turn rests unconformably 
on the upturned edges of the Tertiary shales. At another place the 
sandstone reef has been more or less shattered by the waves, but frag- 
ments of the stone reef rock from three to eight metres long overlie the 
coral reef, and in some cases they overlie coral reefs that rest upon 
granite boulders for a distance of two hundred metres. Again, two 
hundred metres north of Garça Torta there is а coral reef exposed at 
the edge of the beach for a distance of one hundred metres. The rela- 
tions of this reef to the other rocks cannot be seen. At low tide it is 
One metre out of water. 
Out seaward from these beach exposures are more than twenty patches 
of coral more or less isolated. They are generally not more than seventy 
Metres across, — some are less 
than seven metres, — flat on ee Ex sA 
top with openings between ZF £ г gm lt Wirken line 
them. These patches extend eee ne San 
Fra. 99. Coral reef covered by worm tubes 
a kilometre out from th 
пе QU Mon 3 south of Garça Torta. 
beach. South of Garga Torta 
are similar patches. The following is an outline sketch of one of these 
small patches. 
The harbor at Maceio is formed by the southern end of a coral reef. 
This reef is about three kilometres long and varies in width from eight 
