branner: the stone reefs of brazil. 121 



know this, and also to know the angle of the newly exposed surface. 

 It is certainly not to be supposed that a vertical recession of ten fathoms, 

 or anything approaching it, has taken place in thirty years. 



4. Lakes near the coast. — Liais's idea seems to be that the lakes 

 near the coast are produced by elevation and that their basins are the 

 lower portions of the former sea bottom, while Capanema speaks of the 

 shutting off of lakes by sand banks — apparently understood to be 

 banks of submarine origin. 



There can be no doubt that lakes might be formed in this way ; there 

 may be a question as to whether the lakes of the Brazilian coast have 

 been so formed. This question will be considered later. 



5. The fixed dunes of the coast. — Liais assumes that an elevation of 

 a coast on which sand dunes had been forming would put a stop to the 

 beach supply of sand, and that the dunes Avould for this reason cease to 

 move. 



Where it is a question of small vertical elevation, such a result is not 

 to be expected from such a cause. When dunes are once set going over 

 large areas no new supply of sand is necessary to keep them in motion. 

 This is too well known to require discussion. In northern Nebraska, 

 a thousand miles from the sea-coast, are extensive areas covered by shift- 

 ing sand dunes. Many of the great deserts of the world, such as the 

 Colorado desert, the Sahara desert, the Mojave desert, and the deserts 

 of the lofty arid regions of South America, bear witness to this fact. 



If it be assumed that the case is different on the coast-line where the 

 dunes occupy a narrow belt, then it comes to be a question as to whether 

 the dunes along the Brazilian coast are or are not now in motion. As a 

 matter of fact the dunes of this coast, with certain exceptions, are not 

 stationary, as the writer knows both from personal observation and from 

 the statements of other trustworthy writers. The dunes ai-e moving 

 along the coasts of Bahia, Sergipe,* Alagoas, Rio Grande do Korte, 

 Ceara, and Maranhao. In these states the writer has seen many miles 

 of dunes, and they are known to every one wlio has travelled much along 

 the coast. Hartt mentions them in Bahia,' Sergipe, Rio Grande do 

 Norte, and Ceara. Koster also mentions those of Rio Grande do 

 Norte.' In the last-named state the dunes stretch for miles along the 



1 J. C. Branner. The Cretaceous and Tertiary geology of Brazil. Trans. 

 Araer. Thil. Soc, XVI., p. 375. Philadelphia, 1880. 



2 Geology and physical geography of Brazil, p. 345-346; 355; 383; 394; 455; 

 458. 



8 Henry Koster. Travels in Brazil, 2d cd., Vol. I., p. 102. London. 1817. 



