On the outer rim of the cuvette—away from the moisture—hundreds, in fact, thousands of cones, cylinders and domes, from 4 to 6 ft. high, the work of ants, could be seen, all constructed of bluish grey ashes.
We had here a wonderful example, quite sufficient to persuade the most sceptical, of the influence of agglomerations of trees in the formation of clouds. The sky was perfectly clear everywhere except directly above the extensive cluster of trees in the large cuvette. Quite low down—only a hundred feet or so above the top of the trees—there hung a heavy white cloud. It was a windless day. The cloud ended on all sides exactly where the trees ended, as sharply as if it had been cut with a knife. It looked exactly like a rectangular canopy over the luxuriant vegetation. This appearance was intensified by undulations in the lower part of the cloud, like festoons.
In proceeding across the immense circular cuvette I found that the central line of thick vegetation formed an angle. A streamlet of delicious crystal-like water emerged from among the trees. On its bank lay the skeletons of three mules, suggesting a tragedy.
On leaving the great cuvette we rose again to the top of the plateau, 2,550 ft. above sea level. On descending from a large dome to the west over red volcanic sand and red earth, half consolidated into rock easily friable under slight pressure, we were once more travelling across immense campos in a depression of fine cinders and earth, extending from north to south, at an elevation of 2,400 ft. We further traversed two other less important depressions, the deepest being at an elevation of 2,350 ft.
The jutting headlands of the plateau on which we had travelled were all most precipitous—nearly vertical—and of solid dark red volcanic rock.
A magnificent view next confronted us to the south. A huge black square block with a crater was before us, and there appeared what seemed to me to be the remaining sections of a huge volcanic vent and several smaller funnels. The lower lip of the crater formed a terrace. Then another wider crater could be perceived in a circular hollow of the spur of the plateau on which we had travelled, and which stretched out into the underlying plain. That spur extended from north-east to south-west, and in it two circular hollows of great size could be noticed, the sides of which were deeply fluted.
During the entire march that day we had seen quantities of violet-coloured deposits made up of tiny crystals, carbonized and pulverized rock and ferruginous dust.
Central Cluster of Trees and Palms in a Cuvette (Matto Grosso).