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 tlie 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 tliought to be a coral reef. Both ends of the reef are covered by 

 sand spits. 



At Riacho Doce, south latitude 9° 36', and from there to Gar9a Torta 

 are several exposures of coral reefs on shore in addition to the large reefs 

 outside. 



As pointed out 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 bouldei's 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 tliere 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 Gar9a Torta there is a 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 ai'e less /. , ■ ' -^» 



than seven metres, — flat on i:^'"^^'^ ^^^-..k--^- -^ 



top with openings between -£fF—^ — '- ^ ' ^ — ' — 1 — 'H^a&'7,77e. 



them. These patches extend "^^ "^ 



a kilometre out from the ^'^- ^^- ^'^''"^ '^^^ '^^^"^^ ^^' """^"^ ^"^^^ 



south of Gar^a Torta. 

 beach. .South of Gar^a iorta 



are similar patches. The following is an outline sketch of one of these 



small patches. 



The harbor at Maceio is formed by tlio southern end of a coral reef. 



This reef is about three kilometres long and varies in width from eight 



