woomvoRTH: geological expedition to brazil and chile. 51 



thin beds of coal. The lower members of the Permian section display 

 no marked persistence north and south but towards the top of the 

 section more uniform conditions of deposition appear to have pre- 

 vailed. The horizon of the Iraty black shales near the top appears 

 to be fairly continuous. 



The so-called Trias characterised by red beds and contemporaneous 

 basaltic outflows and intrusions marked a great change of geography 

 and climate. Arid conditions succeeded to the moist climate of the 

 Permian but stream action appears to be demanded for the deposition 

 of the thick sandstone beds devoid of marine fossils. Presumably at 

 the close of the Triassic episode of deposition and at some stage in the 

 Jurassic period the region underwent gentle warping producing the 

 present structure of the plateau. 



The Jurassic and Cretaceous periods are in this region without 

 existing remnants of deposits. If the elevated Cretaceous marine 

 beds of the north originally extended so far south, it is to l)e presumed 

 that they were preceded by an epoch of baselevelling and in the 

 following Tertiary time by the uplift of the district in such a manner 

 as to give rise to the Serra do Mar slope to the sea-floor. Erosion of 

 the plateau surface and of the short slope to the sea has worked out 

 in accordance with the specific resistances of the several terranes the 

 existing topography of the region, with a late Tertiary interruption of 

 the cycle of erosion indicated by small basins of non-marine Tertiary 

 beds in Sao Paulo. Over this surface a mantle of unconsolidated 

 materials produced by weathering with more or less transportation 

 has accumulated during Pleistocene and Recent times. 



The annexed cross-section of south Brazil, after Derby, exhibits the 

 essential features of the structure of the plateau in the latitudes where 

 the Devonian strata occur. 



FiQ. 9. — Geological cross section of south Brazil (after Derby). 



For a bibliography of Brazilian geology, the catalogue of publica- 

 tions prepared by Prof. J. C. Branner (1909) should be consulted. 



