branner: the stone reefs of brazil. 



Ill 



V. 



The Elevation and Depression of the Northeast Coast of 



Brazil. 



PAGE 



Changes of the reefs within his- 

 toric times Ill 



Changes within recent geologic 



periods 118 



Views of former writers . . . 118 

 Schistose structure of reef 



rocks 119 



Dip of the reef rocks . . . 119 

 Reef rocks above high tide . 120 

 Lakes near the coast . . . 121 

 Fixed dunes of the coast . . 121 

 Islands joined to mainland . 122 

 Straightening of the coast- 

 line 124 



Comparative effects of ele- 

 vation and depression . . 125 

 Effects of elevation . . . . 125 

 Effects of depression . . . 125 

 Forms on a stationary coast 127 

 Application to Brazil .... 127 

 Evidences of depression . . . 127 



Open bays 128 



Coast lakes 129 



PAOE 



Rios tapados 134 



Choked embayments . . . 137 

 Depressed valleys .... 139 

 The case of Rio Sao Fran- 

 cisco 143 



Islands 144 



Off-shore clays 144 



Buried rock-channels . . . 145 

 Additional views of depres- 

 sion 146 



Evidences of elevation .... 148 



Elevated sea beaches . . . 148 



Elevated sea-urchin burrows 159 

 Death and decay of the coral 



reefs 159 



Time relations of the elevations 



and depressions .... 162 



Influence of the coral reefs . 164 

 Influences of the mangues, 



hyacinths 167 



Origin of the coast sands 167 

 Conclusions regarding coast 



changes 169 



Changes of the Reefs within Historic Times. 



There are, perhaps, but few coasts of considerable length on which 

 there are not evidences of both elevation and depression. Along the 

 west coast of North America, for example, wave-cut terraces upon the 

 slopes of the hills and mountains near the coast show that there have 

 been several recent elevations of the land, while well-defined submerged 

 valleys,^ the distribution of the fish faunas in fresh-water streams, 

 and the relations of fauna and flora of the islands oft' the coast to those 

 of the mainland show that there have also been recent depressions. 



Observations of others. — Humboldt and Darwin show that there has 

 been a recent elevation of the northern end of the South American con- 



1 George Davidson. The submerged valleys of the coast of California, U. S. A., 

 and of Lower California, Mexico. Proc. Cal. Acad. Sci., 3rd ser., Vol. I., p. 71-103, 

 and plates. San Francisco, June, 1897. 



