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 во 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 would 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 caso 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, Asa 
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 are moving 
along the coasts of Bahia, Sergipe,! Alagóas, Rio Grande do Norte, 
Ceará, and Maranhäo. In these states the writer has seen many miles 
of dunes, and they are known to every one who has travelled much along 
the coast. Hartt mentions them in Bahia,? Sergipe, Rio Grande do 
Norte, and Ceará. 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. 
Amer. Phil. Soc., XVI., р. 375. Philadelphia, 1889. 
2 Geology and physical geography of Brazil, p. 845-346 ; 355; 883; 394; 455; 
8 Henry Koster. Travels in Brazil, 2d ed., Vol. L, р. 102. London, 1817. 
