CORRIDEIRAS 
unlike parallel small dunes of sand with a deposit of 
gravel upon them. For 700 metres the river was 
obstructed and navigation became rather troublesome. 
Where the river turned from bearings magnetic 310° 
to 360° (due north) we went over a nasty stony place 
with a strong corrideira above it, and we were confronted 
with a rocky barrier almost the entire width across the 
stream. We kept on the west side, the only way where 
it was possible to get the canoe through. A little farther 
another corrideira, stronger than the first, obliged us to 
find a passage on the east side of the river — which bore 
upon its bank campos and chapada . Curious mounds of 
white sand and gravel were visible in the centre of the 
river, and also near the left bank below the second 
corrideira; then we came to parallel ridges of white 
sand and gravel right across the river bottom at an 
angle of 45° in relation to the general direction of the 
stream. 
Two tributaries, one three metres wide on the left 
bank, the other four metres wide on the right side (the 
latter coming from the northeast), swelled the Arinos 
from that point. The width of the stream was now 
increased to eighty metres, the water being shallow. 
The bed of the river was ever changing, and supplied 
me with constant interest. It was adorned with strangely 
precise triangles of beautiful white sand exposed through 
a layer of gravel which covered most of the river 
bottom. 
A thickly wooded hill range, 150 feet high and 
extending from west-southwest to east-northeast, stood to 
the north of us. Its slopes, eroded by the water, had 
caused a landslip, leaving bare vertical red rock for half 
the height of the hill-range and two much eroded spurs 
of bright yellow and white earth extending into the 
stream. 
The river at that point turned from north to east. 
47 
