We now had most beautiful forest on both sides. A stream 5 m. wide joined the Arinos on the left side from the west, forming a charming little waterfall as it entered the main stream. A little farther on the right was another streamlet, coming from the south-east. Generally, as in this case, when we reached tributary streams of any importance, gravel banks extended and blocked a great part of, sometimes even half, the main stream.
A picturesque stream, 8 m. wide, coming from the north-east, was then reached on the right side. It flowed through a rocky gate. Five or six kilometres farther on a tiny streamlet dribbled into the Arinos, and also another, 1 m. wide, on the left bank.
At noon that day the sky was extraordinarily interesting. From the north-west extended a wonderful succession of loop coils of transparent mist, giving the sky the appearance of a peacock's extended tail.
Just before we halted for lunch we came to a charming streamlet of delicious water, 2 m. wide, on the right bank.
The days were getting warmer as we advanced farther north. It was hot work sitting in the sun—105° F. that day—to take observations for latitude and longitude. In the shade the thermometer registered 89° F. Lat. 12° 21′·3 S.; long. 57° 16′ W.
After lunch, 2½ kil. from our camp, we passed on the left bank a delightful tributary coming from the W.S.W. Its mouth was 8 m. wide, and poured forth waters of the most beautiful emerald green.
Five hundred metres farther down another large tributary, 30 m. wide, coming from the north-east, was observed on the right bank. Farther still, the river formed a large basin 300 m. wide. Lovely forest flourished round the sweeping curve of the basin. There was simply a solid mass of marvellously fresh foliage, with hardly a break through which, it seemed, a human being could pass. In that particular part the leaves came right down to the water, but there was no reason to suppose that they grew equally low inland.
The stream, which was 250 m. broad, showed farther on an immense bank of gravel 700 m. long, which rose above the surface in the shape of two long islands—one 300 m., the other 400 m. in length.
We felt the heat considerably going down the river, as we were always in the sun in the centre of the stream, with a temperature seldom less than 105° F. Especially where thick forest was on both sides of us, there seemed to be no air close to the water. When we came to patches of chapada and open country we could breathe a little better. Several were the tributary streamlets to which we came that afternoon. First we saw one rivulet, 1 m. wide, on the right bank, then 13 kil. 500 m. farther on another affluent, 3 m. wide, coming from the north-east, also on the right bank; then 1,500 m. farther a rivulet ½ m. wide, coming from the south-west (left bank); then 4,500 m. farther a charming stream, 6 m. wide, coming from the north, and meeting with the Arinos near an extensive stony place with shallow and troublesome water. Strong eddies formed at that spot. One more streamlet, 1 m. wide, was reached that day on the right. It came from the north-east.
The river had that day flowed almost continuously in directions varying from north-west to north, barring two sections where its course had been 10° east of north.