WOODWORTH: GEOLOGICAL EXPEDITION TO BRAZIL AND CHILE. 107 
“stage of the river presumably was developed on the surface of the 
Tertiary beds. 
The divide between the Tieté at Mogy das Cruzes and the great 
bend is occupied by rock-hills of low relief rising about 200 feet above 
the weakly developed drainage lines of the district. The natural 
course of the Parahytinga would appear to be westward into conflu- 
ence with the Rio Tieté of which it may be regarded as a beheaded 
portion, captured by the Rio Parahyba, which, pushing its head 
southwestwards along the easily eroded Tertiary beds, diverted the 
stream before erosion had swept away the Tertiary beds between the 
Parahyba basin and that of the Tertiary beds at Sao Paulo. 
The Pleistocene and Recent Formations.— The discrimination of the 
Post-Tertiary changes in extra-glacial regions into Pleistocene and 
Recent is attended with difficulties. In Brazil the surface deposits 
are prevailingly residual clays or clays, sands, and pebble beds derived 
from the secular washing and transportation of weathered Pre- 
Pleistocene formations. Great differences exist as to the depth of the 
decayed rock even on the same formation. Where the rainfall is 
heavy at certain seasons of the year, the slope of the ground steep, 
and the run-off effective, the decayed materials are removed nearly as 
fast as their disintegration or decomposition is accomplished and thus 
nearly fresh rock occurs at the surface. I was frequently surprised 
in the valleys of the Rio Negro and the Rio Tuberao by the apparent 
freshness of carbonaceous shales at a depth of a few centimeters be- 
low the surface but in these situations erosion has been and still is 
actively in progress. 
The new cuts of the railway in construction from Bury in Sao 
Paulo via Sao Pedro de Itararé and Jaguariahyva to Ponta Grossa 
in Parand gave at the time of my visit an unusual opportunity to see 
many excavations in the mantle rock. Along the banks of the Rio 
Jaguaricatu in the Permian tillite beds these cuttings were often from 
5 to 10 meters deep. At these depths most of the pebbles were still 
undecomposed. 
At numerous localities along the railway line across the mature 
topography of southern Sao Paulo and Parand the rounded swells 
between streams display tracts of ancient gravel beds usually with 
concave lower limits as if occupying old stream channels long since 
abandoned. The same phenomenon is observable in a pronounced 
manner where the railway from Ponta Grossa to Serrinha Station in 
Parana skirts the lower westward slopes of the sandstones of the 
Devonian cuesta. In all these cases the history of the surface appears 
