104 bulletin: museum of comparative zoology. 



The Devonian shales in central eastern Parana give rise to a longi- 

 tudinal valley but the non-resistent character of these rocks is locally 

 counteracted by intrusions of diabase. The western side of this 

 longitudinal valley, where it is developed, is formed by sandstones and 

 conglomerates of the basal Permian. Ponta Grossa stands on the 

 western side of this valley. 



The sandstone and conglomeratic members of the Permian form an 

 irregular grouping of uplands separated by river valleys. The level 

 at which the hilltops stand, intermediate between that of the lowlands 

 and the trap plateau and the Devonian cuesta probably indicates 

 an intermecliate stand of the land, the date of which is difficult 

 to determine. The valleys of such rivers as the Tiete in Sao Paulo 

 certainly have been excavated since the Tertiary deposits which 

 underlie the city of that name. It seems highly probable therefore 

 that the uplands in the Permian tracts antedate not only these Tertiary 

 deposits but also the erosion of the depressions in which the beds were 

 accumulated. The date of the evanescent peneplain with which the 

 summits of the upland areas accord must be placed therefore in early 

 Tertiary time. 



The westward flowing drainage of the planalto gives rise to the 

 dissection of the Permian terrane by long westward aligned valleys 

 such as those of the Paranapanema and the Rio Negro, but the 

 tributaries of the latter river including such large streams as the 

 Tibagy flow obliquely across the trend of the Permian belt on courses 

 expressing the resolution of the double control of the westward dip of 

 the formation on the one hand and of the slope towartls the master 

 stream developed by concentration of the drainage on the other. The 

 Rio Negro displays a rectangular adjustment of its course to the 

 strike and dip of the Permian strata. 



In the latitude of Curityba there is traceable westward from the 

 vicinity of that city a divide between the waters which drain northward 

 into the Paranapanema and southward into the Rio Iguassu. This 

 watershed includes the Serrinha, passes south of the towns of Pal- 

 meira and Iraty and thence joins on the west the trap escarpment 

 known as the Serra da Esperan^a. The great extent of the drainage 

 basin of the Rio Paranapanema as compared with that of the com- 

 bined Iguassu and Rio Negro in the Permian terrane is apparently a 

 consequence of the antilinal axis, which, normal to the arc of the 

 outcrops in eastern Parana and southern Sao Paulo, caused the 

 Palaeozoic beds along this east-west line to stand relatively high and 

 erode more rapidly. As a result of this distribution of the drainage 



