Northeast Coast of Brazil. 



385 



in texture and hardness between the material of the reefs and 

 that of the cliffs ; but in most places the reef-forming portion 

 is harder, heavier and more nearly rust-color, and it appears 

 that concentration of the iron has taken place in those places 

 subjected to the action of the sea-water. In many places where 

 the red sandstone is not in evidence as cliffs, reefs of the 

 material are exposed along the shore, and probably the greater 

 number of the reefs along the northeast coast of Brazil are of 



Fig. 11. 



Fig. 11. Blocks of iron-cemented sandstone at Ponta Eedonda. 



this material. The approximate extent of these reefs along 

 the portion of the coast under consideration is indicated on the 

 general map of PI. IX. They are also present farther to the 

 north and to the south. In many places the material is an 

 iron-cemented gravel, rather than a sandstone ; but it appears 

 to be made up of fragments of the coastal sandstone, recemented 

 together. The wide distribution of the iron-cemented reef- 

 forming material is notable. It is exposed at the base of a cliff 

 of light-colored sediments on the north side of the harbor of 

 Maranhao, 250 miles west of Camocim, and extends far toward 

 the channel of the harbor at low tide. At the immediate base 

 of the cliff there are bowlders in which the iron is heavily con- 

 centrated. Even along the Amazon River the concentration 

 of the iron at or about tide level seems to have taken place in 

 the red sediments, as is shown notably at the base of a bluff 

 on the north bank, TOO miles above the river's mouth, between 

 the villages of Parintins and Itacoatiara. 



