woodworth: geological expedition to brazil and chile. 99 



of decomposed rock may be observed to a depth of over 100 feet, the 

 surface of the still solid rock imderneath presents ridges and hollows, 

 succeeding each other according to Aarying durability under the 

 influence of percolating carbonated water. In this kind of weathering, 

 where erosion does not come into play, it is evident that the resulting 

 topography must, in some important respects, differ from that of an 

 ordinary surface of superficial denudation. In particular, rock basins 

 may be gradually eaten out of the solid rock. These will remain full 

 of the decomposed material, but any subsequent action, such as that 

 of glacier ice, which could scoop out the detritus, would leave the 

 basins and their intervening ridges exposed." 



VII. GEOMORPHOLOGY OF SOUTH BRAZIL. 



In the preceding chapters so much has been stated concerning the 

 form and relief of the tableland of south Brazil, in describing the 

 structure and position of the Permian glacial beds, that little remains 

 in treating specifically a sketch of the geomorphology of the region 

 than to summarize the matter in more systematic terms with the 

 added enumeration of certain details. 



Regarded as a land form south Brazil is an elevated tableland with 

 a short steep slope descending to and below the Atlantic sea-level and 

 a long gentle slope towards the interior of the continent. The surface 

 of this warped mass appears to have been in Cretaceous times muchi 

 more nearly a plane. Since its elevation and warping it has beeni 

 dissected by streams which have etched out the structure of the 

 westward clipping beds of the long westward slope into lines of escarp- 

 ments formed of the edges of the harder more resistent beds over- 

 looking lowlands. 



For convenience of treatment the region may be divided into two 

 districts which by their geological nature and relief at once impress 

 the visitor to Brazil. First, the steep coastal border of the Serra do 

 Mar, and second, the tableland or planalto proper. 



The Serra do Mar, notched and pinnacled in the states of Rio de 

 Janeiro and Sao Paulo, declines to the southward, and in Santa Catha- 

 rina retains more of the character of the warped surface of mature 

 relief which appears to have been characteristic of the whole belt in 

 an early stage of its development following the warping above noted.. 

 In eastern Parana the summits of the Serra do Mar form a line of 

 peaks and ridges rising well above the eastern portion of the tableland 



