WOODWORTH: GEOLOGICAL EXPEDITION TO BRAZIL AND CHILE. 105 
the headwaters of the Rio Paranapanema drain almost entirely the 
western slopes of the Devonian beds, as does the Ribeira de Iguape the 
crystalline terrane on the east of the Devonian sandstones. 
The Permian tract is bounded on the west by the Triassic escarp- 
ment of sandstones crowned by trap sheets. The westward dip of the 
formation combined with the flow of the streams in that general 
direction has caused the trap to retreat far to the west along the axis of 
the main drainage lines, such as that of the Paranapanema and the 
Iguasst. In the western part of the south Brazilian states of Sao 
Paulo, Parana, and Santa Catharina the rivers flow over the trap 
sheets whose resistance to erosion holds up to their local baselevel 
the entire drainage area of the planalto. The Rio Parandé on the 
confines of Brazil and Uruguay is gnawing back the southern edge of 
the trap sheets. Below the cascades and falls the river joins the 
drowned valleys of the La Plata system. 
The rate at which the falls of the Parana and Iguassti are receding 
has not I believe been determined. But it is evident that the rivers 
have cut back from the southern edge of the trap sheets since the land 
had something like its present elevation above the sea. If the land 
at the confluence of the Iguassti and the Parana had been as long above 
sea-level as it has in the upper valley of the Iguassti, where the trap 
has been swept away over a large tract of the Permian, it is incon- 
ceivable that the youthful characteristic of falls and cascades should 
still persist. We are therefore compelled to conclude that the country 
immediately adjacent to the Parana and Paraguay rivers has recently 
been uplifted in relation to the sea. As on the south of the trappean 
country in Banda Oriental there are marine Tertiary beds now above 
sea-level (Darwin, 1846, p. 1-3) and as along the coast of Brazil 
from north of Rio de Janeiro to the Amazon (Derby, 1907, p. 218-237) 
there are evidences of uplift since the Tertiary beds were there laid 
down, it seems a valid hypothesis that the excavation of the Parana 
channel in the traps began in later Tertiary time through an uplift 
of the whole planalto of Brazil. 
The upper courses of small streams in eastern Sao Paulo and 
northern Parana generally flow in narrow gorges so recently cut that 
many side streams particularly of the wet-weather type enter by a fall 
over the brink of the gorge. Without a thorough understanding of 
the local baselevels of the Parana system it seems out of the question 
to infer the cause of this revived stream-action. 
. A remarkable example of one of these streams is the Rio Itararé 
flowing north into the Paranapanema along the boundary between 
