WOODWORTH: 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 be 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. 
Serra da uaapann ¢ 
goers ee Ak 
. Ct We 
Ports Grosser et ASerra doMar 
C ; € 
Fia. 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. 
