On entering the wider part of the valley, we perceived before us, insulated in the middle of the plain, an immense circular elevation, rising nearly to the level of the surface of the sandstone table, and apparently inaccessible upon all sides. On its summit { 278} is a level area of several acres, bearing a few cedar bushes, probably the habitation of birds only.
Leaving this, we passed three others in succession similar to it in character, but more elevated and remarkable. Of one of them, Mr. Peale has preserved a drawing. After passing the last of these, the hills ceased abruptly, and we found ourselves once more entering a vast unvaried plain of sand. The bed of the creek had become much wider, but its water had disappeared. Meeting at length with a stagnant pool, we halted to dine, but found the water more bitter and nauseous than that of the ocean. As it could neither be used for cooking or to drink, we made but a short halt, dining on a scanty allowance of roasted venison, which we ate without bread, salt, water, or any thing else. Some fragments of amygdaloid were strewed along the bed of the stream, but we saw no more of that rock, or of the other members of the fletz trap formation in place. They may extend far towards the south-west, but of this we have no conclusive evidence. The aspect of these rocks, particularly of the amygdaloid or toad stone, is so peculiar, and its disposition so remarkably dissimilar to that of the sandstones with which it is associated, that nothing seems more natural than that it should be referred to a different origin.
In the midst of one of the violent storms we encountered in passing this trap formation, we crossed the point of a long and inconsiderable elevated ridge of amygdaloid, so singularly disposed as to suggest to every one of the party the idea that the mass had once been in a fluid state; and that, when in that state, it had formed a current, descending along the bed of a narrow ravine, which it now occupied, conforming to all the sinuosities and inequalities of the valley, as a column of semifluid matter would do. Its substance was penetrated with numerous vasicular cavities, which were observed to be elongated in the direction of the ridge. Its colour is nearly { 279} black, and when two masses are rubbed together, they yield a smell somewhat like the soot of a chimney. These appearances are so remarkable, that it is not at all surprising these rocks should have been considered of volcanic origin; and it is this supposition unquestionably from which has originated the statement contained in the late map of the United States by Mellish,[54] that the district about the sources of Red river is occupied by volcanic rocks; the information having probably been derived from the accounts of hunters.