400 ORVILLE A. DERBY 



during a part of the Tertiary age, were such that an inland basin was 

 filled up with horizontal deposits nearly to the level of the surround- 

 ing denudation plain, and later, through a rise in the land, both 

 were dissected to a depth of 200 to 300™. About the same 

 amount of elevation is indicated by the coast Tertiary beds, by the 

 Cretaceous strata near the Paulo Alfonso cataract, and by the dis- 

 section of the denudation plain and horizontal Cretaceous ( ?) strata 

 of the upper Sao Francisco basin; so that this movement may be 

 taken to have been general and of approximately equal amount 

 throughout the whole region. The Cretaceous strata of the Paulo 

 Alfonso region seems to have been laid down on a still older denuda- 

 tion plain, which must have stood at about the level of the sea, since 

 the fauna contains a mixture of fresh- water and marine forms (cyprids 

 and sharks). The denudation of the mountain zone was therefore 

 effected by successive stages, and under different conditions of drain- 

 age and elevation; and to this circumstance are doubtless due many 

 of its topographic characteristics. 



BIBLIOGRAPHY 



1. Eschwege, W. L. von. Geognostisches Gemdlde von Brasilion und das wahr- 



scheinlichen Mutter gestein der Diamanten. Weimar, 1822. 



2. Beitrdge zur Gebirgskunde Brasiliens. Berlin, 1832. 



3. Spix und Martius. Reise in Brasilien. Munich, 1823-31. 



4. Helmreichen, Virgil von. Ueber das geognostische Vorkommen der Dia- 



manten und ihre Gewinnungs-Methoden auj der Serra do Grao-Mogor. 

 Vienna, 1846. 



5. Henwood, Wm. J. "Observations on Metalliferous Deposits of the Gold 



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