One kilometre farther a conglomerate mass of granite and yellow and red lava, with impurities embedded in it, emerged just above the water in the centre of the stream.
Another streamlet, 2 m. wide, and of wonderfully limpid water, joined the Arinos on the right side. It came from the north-east. Then another little streamlet was seen on the left side.
At the end of 10 kil., where the river made a wide angle from 330° b.m. to 350° b.m., and another straight line of 4,000 m. stretched in front of us, we beheld a huge submerged bank of sharp volcanic conglomerate rock. In fact, we unexpectedly almost ran into it. Had we done so at the rate at which we were travelling, our canoe would certainly have been smashed to pieces against the sharp-edged fractured rock—just as sharp at the angles as the blades of knives.
Where the river turned once more from 350° b.m. to 320° b.m. another small tributary appeared on the right bank, and there a lot of handsome mate trees (Ilex paraguayensis) seemed to flourish, and were certainly pretty to look at.
Farther down we again came to chapada on the left bank and heavy foliaged forest with a certain number of rubber trees on the right bank. The left bank, where it described a great sweeping circle, was low and sandy, some 12 ft. above the level of the river. Only a thin fringe of low trees grew there on the edge of the water.
Six kilometres from the last tributary on the right bank another streamlet, 3 m. wide, coming from the S.S.W., cut its way through the left bank. Two thousand five hundred metres farther on another tributary 20 m. wide—a deliciously beautiful stream—flowed gracefully into the Arinos on the right side from the north-east.
We made our camp at the junction of the two streams. The camp was extremely bad. It was already late in the evening and we could find no other suitable spot. We had gone that day 83 kils. I was quite satisfied with the progress we had made during the last few days. During the evening I made an excursion on foot along the tributary river to the north-east for several kilometres, but I found nothing of particular interest.
During the night we received another visit from an anta, but the pachyderm again escaped before my men had time to kill it. We heard cries of Indians in the distance. My men were in a great state of mind for fear we should be attacked. I sat up the entire night in order to be ready in case of emergency.
I took that opportunity of computing and checking many of the astronomical observations I had taken, and developing a great number of photographic glass plates.
In my experience I have found that the fears people have of spoiling negatives unless one is shut up in an absolutely dark room are quite exaggerated. On that particular occasion, for instance, and on many previous and subsequent occasions, I developed the glass plates—and I think with satisfactory results—out in the open, with merely the fly-leaf of the tent sheltering me overhead so as not to have the direct rays of the stars shining upon the photographic plates. Indeed, there was light enough coming in around the tent for me to see quite plainly what was going on outside. I simply covered up the developing trays as an extra precaution, and seldom—in fact, never—spoiled a negative in process of development.