The minimum temperature of August 12th had been 70 deg. F., whereas during
the night of August 13th it was 62 deg. F.

That little adventure had pulled the men together somewhat. I spoke in
great praise of the courage that Antonio and Filippe had shown in
swimming across the stream.

The river was smooth for a little distance, when we proceeded once more
with our navigation; but soon it became narrow--only 40 to 50 m.
wide--with strong eddies in its deep channel between rocky sides. Some
magnificent sand beaches 15 to 20 ft. high were observed, particularly on
the right bank, not far from a tributary 3 m. wide which entered the main
river on the left side. Lower down, the river described a sharp turn, and
there we met another most dangerous rapid. It was entered by a passage 50
m. wide, after which a circular basin of rock--evidently an ancient
crater--100 m. in diameter appeared; then the water flowed out with
terrific force by a channel only 30 m. wide. The stream produced
prodigious eddies in the circular basin. Waves of great height were
dashed to and fro from one side to the other of the narrow channel,
between high rocks on either side. The water flowed first in a direction
E.S.E. for 500 m., then turned off suddenly to due east for a distance of
400 m. That spot was most difficult for us to go through.

Soon after, the river turned due north and broadened to a width of 120 m.
for some 4,000 m. A great basin was crossed, with submerged rocks,
forming counter currents of great power and most unpleasant whirlpools. I
observed with some concern a stupendous vortex 30 m. in diameter and with
a deep central depression. The water revolved with such velocity and
force that it formed a series of high-crested white waves running one
after another at a terrifying speed around its periphery. The water was
raised around the vortex certainly 10 or 12 ft. above the level of the
river--owing to the opposition between the rotating water and the
current. We gave that vortex as wide a berth as we could; it really
frightened one to be near it, although there was no particular danger
unless we got right into it.

A charming island was passed soon after, on which, as well as on the left
bank, were innumerable rubber trees, but there were none on the right,
where _chapada_ was to be seen.

We had in front of us a hill range 300 ft. high. As we went farther we
were in a channel between high rocks strewn about along both banks in