The scene which I had before me there in Matto Grosso greatly reminded me of a similar basin I had seen when the great Bandaisan mountain in Japan was blown up by a volcanic explosion and left merely the bottom part of its gigantic internal cauldron with vertical red walls around it. With the exception of scanty and anæmic grass and a few stunted trees, there was hardly any vegetation noticeable. The Fogasso stream, on the bank of which we camped, flowed in an easterly direction into the Araguaya.
The temperature on the plateau was ideal—min. 63° Fahr. during the night; max. 75°. We were at an elevation of 1,450 ft.
On May 15th we were travelling along a valley over which must have once risen the continuation of a range which stood to the north of us. There were deep grooves and corrugations in the valley in a direction from south to north between the two sections of the now interrupted range. There we found soil of red, brown and yellow tints, or else great stretches of grey volcanic ashes and earth mixed, as well as sharply angular fragments of igneous rock, which showed that they had not travelled there by rolling on the ground or propelled by water.
After this we passed close to another curious spur of mountains on the east—quite isolated and of a red vertical columnar formation. Its summit was broken up—much more so than that of the plateau-like range to the south of us which we were following in a parallel line. The highest point of that range, to the south, was wooded, and so were the two conical-topped hills which towered over it. The strata where exposed showed a slight dip to the north. We crossed the range by two low cols at elevations of 1,550 ft. and 1,560 ft. respectively. On the summit and even lower upon the sides of those cols we found huge boulders of eruptive rock, highly ferruginous. Globular lumps, big and small, of spattered smooth-surfaced yellow lava were to be found in myriads; also many spherical pellets of ferruginous, highly-baked rock with innumerable holes produced while in a state of ebullition. Some of the ferruginous rocks had pellets of yellow lava firmly imbedded in them, which had evidently penetrated while liquid into the hollows of the ferruginous rock which was already in a semi-solid, or perhaps solidified, condition. At any rate, when it happened the ferruginous rock was already harder than the lava.
While I was studying attentively the geological conditions of that region, the sky suddenly became as black as ink to the south, and a heavy shower, which lasted half an hour, drenched us all to the marrow of our bones. Then it cleared up, and the sun, supplemented by our natural heat, dried our clothes upon us again as we went on.
CHAPTER XII
Geological Speculation—Beautiful Pasture-land
The stars were of extraordinary brilliancy at night; so much so that one could see quite well enough by their light to get about. The atmosphere being extremely clear, they appeared of immense size, the planets shining with dazzling, changing colours which would have filled even the most profane with reverence for their splendour.