I9I3-] REGION ABOUT NATAL, BRAZIL. 435 



The sea is shallow along the coast, and one sees this especially 

 when watching the natives setting their jangadas afloat by pushing 

 them along the wide, gently sloping beaches. Often at the end of 



FiG.*2. General cross-section of the sandstone reef at Natal, Rio Grande 



do Norte. 



one of the prominent points, as that of Pirangy, it may be noticed at 

 low tide that the rocks extend for a considerable distance and then 

 an organic reef, containing corals and other marine animals, con- 

 tinues far out to sea, forming a flat shelf for some distance. These 

 organic reefs do not occur near shore, for the waves are full of 

 sand, scooped up from the shallow bottom. The ships cannot come 

 near shore, except through certain channels as that of Natal, where 

 the animals that make up the reefs cannot live on account of the 

 fresh water from the river. 



The Valleys. — The most striking feature about the river valleys 

 is their extreme width in comparison to their shallow depth. A small 

 stream like the Rio Ceara-Mirim may flow through a valley two and 

 a half kilometers wide not much more than fifteen meters below the 

 surrounding region. The banks which fringe the wide valleys expose 

 red iron-sandstones, covered with sand or a sandy soil. The valley 

 alluvium is a darker black sandy deposit. The whole floor of the 

 valley is flat, with a sluggish stream flowing down its center, 

 bordered by swamps. The natives, whose mud houses are scattered 

 or clustered in villages along its low sides, use it to advantage 

 and cover most of the valley with their banana, corn, cotton, and 

 sugar-cane fields. In some places, such as Ceara-Mirim, the region 

 is very fertile and a growth of shrubs, trees and carnahuba palms 

 covers the valley. 



The valley, on the side of which Natal is situated, is about six 

 kilometers wide, but most of this territory is silted up by mangrove 

 swamps. The sea enters it and at high tide flows up to Macahyba 



