64 J. C. BRANNER — GEOLOGY OF NORTHEAST COAST OE BRAZIL 



This granite is beautifully veined with quartz, some of the veins being 

 a meter thick. Gigantic blocks are exfoliating on an impressive scale. 

 From 200 to 300 meters offshore is a small barren rocky island of this 

 same granite. The hills of the granite on the landward side of the beach 

 are 30 or 40 meters high. A little more than a kilometer south of Pedra 

 do Porto is another exposure on the beach of the same kind of granite. 

 This place is called the Pedra do Conde, and near the beach the granite 

 blocks are beautifully exfoliated. About half a kilometer south of the 

 Pedra do Conde are two round bare islets of granite about 150 meters 

 offshore. 



Soulh of this point there are no granites or other crystalline rocks ex- 

 posed in place on or near the beach as far as Maceio. The rocks seen 

 in place are all Tertiary or recent. The particolored cliffs visible at so 

 many places along the coast are all Tertiary sediments. At a few places, 

 however, there are large granite boulders exposed on the beach and 

 underlying the Tertiary beds. On account of the large size of these 

 boulders, some of them a meter or more in diameter, it is assumed that 

 the granite in place is very near the surface wherever they are found. 

 The following are the places at which the granite boulders occur on the 

 beach : Camaxo, south of Maragogy on the coast of Alagoas ; Barreira 

 do Boqueirao just north of Rio Porto Calvo ; Morro de Camaragibe 

 about 3 kilometers south of Rio Camaragibe, and Riacho Doce just north 

 of the village of this name. 



The following is Mr Turner's description of the granite found at the 

 mouth of Riacho Doce : 



" Microscopically it is a medium grained granite composed of orthoclase, micro- 

 cline, oligoclase, and quartz. The quartz occurs in aggregates of interlocking 

 grains of smaller size than the feldspars. There is a small amount of a yellow- 

 brown nearly opaque substance filling cracks and forming rhombic crystals, pre- 

 sumably secondary. There is a little muscovite and black opaque grains, appar- 

 ently iron-oxide." 



The observations made along the coast on the stone and coral reefs 

 and on the geographic development of the region are reserved for a 

 separate paper. 



RESUME OF THE GEOLOGY OF THE COAST SOUTH OF PERNAMBUCO 



1. The Tertiary rocks form only a narrow coastal belt between Per- 

 nambuco and Maceio ; they are nowhere more than about 14 kilometers 

 wide. 



2. The underlying crystalline rocks are exposed on the coast at only 

 four places between Pernambuco and Maceio : at Pedras Pretas, Cabo 

 Santo Agostinho, Santo Aleixo, and Pedra do Porto. 



