On the west side, on descending the last prominence we at last came to a slight variation in the geological composition of the country. After more white sand and ashes had been passed, we came upon great stretches of greenish grey granite exposed in huge domes and much striated, with parallel grooves on its surface so deep that they almost looked as if they had been incised by a sharp tool. These grooves were, nevertheless, naturally caused by the sharp friction of sand and water, I think, and also by sand blown over those rocks with terrific force by winds of inconceivable vigour. All the way down our descent we travelled over that striated rock. It had become exposed to the air, but must have once been buried under sand and ashes like all the rest of that region. Curious vertical cracks were to be noticed in several places, with ramifications from a common centre—evidently caused by the concussion of some huge weight which had fallen from above, perhaps a huge boulder shot out by volcanic action, which had then rolled farther down the incline.
The terminal side of the curious range we had on our right appeared not unlike a fortress with its vertical walls standing upon a slanting bastion.
At the bottom (elev. 1,200 ft.) of the great dome of granite we had travelled upon we crossed a stream flowing south-west, the water of which was quite warm. The high temperature was due, I think, to the heat absorbed by the rock exposed to the sun and communicated to the water flowing over it, rather than to a thermal origin.
Continuing our journey, we had to the south a great hollow basin in the south-western end of the range, with two hillocks between the range itself and the flat boundary plateau to the south.
The highest point of the hill on which we travelled was 1,450 ft. above the sea level. Every metre we travelled westward became more strangely interesting. We were now upon a conglomerate of bespattered lava-drops encased in a coating of solidified ashes. When we reached the stream we had to go through a dark tunnel of dense vegetation, great ferns, giant palms, creepers with their abundant foliage, and tall trees festooned with liane. Having crossed this dark vegetable passage, we emerged once more into lovely open campos.
Great lumpy globular woolly clouds faced us in the sky to the west. Horizontal intermittent white layers were close to the horizon to the east, then three parallel lines of feathery mist to the north-west. In quantity of clouds the sky that day would meteorologically be described as C 4—which means that four-tenths of the sky vault was covered.
One could not help being struck in Central Brazil by the almost absolute immobility of the clouds. One seldom experienced a strong wind; contrary to what must have taken place there in ages gone by, when that country must have been the very home of terrific air-currents and disturbances on a scale beyond all conception. It was only occasionally that a light breeze—merely in gusts of a few seconds—would refresh one's ears and eyes as one marched on. What was more remarkable still was the sudden change of direction of those spasmodic gusts of wind when they did come.
From a river (elev. 1,250 ft.) we proceeded over undulations to 1,550 ft. There we were treated to an extensive and beautiful view to the west, south-west and north-west. The elevated sky-line formed by the plateau and mountains was quite straight, barring three much eroded mountains standing quite isolated and at a great distance from one another.
One of these solitary elevations was to the south-west, another—the castle-like mountain of great height we had already observed—stood due west. Then came the long flat line of the plateau but for a gentle convexity at each end. The plateau, dressed in thick forest, stood in the middle distance to the west-south-west. Campos of great beauty were prominent on its slopes and in the two hollows in the immediate vicinity.
As we wound our way forward we found masses of ferruginous black rock, black débris, and beautiful crystals.