On the preceding day we had commenced our accustomed march in a valley bounded by perpendicular cliffs of red sandstone, having an elevation of at least two hundred feet. As we ascended gradually along the bed of the stream, we could perceive we were arriving near the surface of this vast horizontal bed of sandrock, and at night we pitched our tent at the very point where the red sandstone began to be overlaid in the bed of the creek by a different variety. This second variety, the gray sandstone, is a horizontal stratum, evidently of more than two hundred feet in thickness. It is usually more compact and imperishable than the red, its fragments remaining longer entire, and retaining the angles and asperities of the surface, which in the other variety are soon softened down by the rapid progress of disintegration. It is easy to perceive that the sandstone formation, including the two varieties above mentioned, {264} must be at this point of immense thickness. Fifteen hundred feet is probably a very moderate estimate for the aggregate elevation of some insulated, but extensive portions of the gray sandstone, above that part of the valley at which the red sandstone first appears. From this point downwards, the extent of the latter variety may be very great, but no estimate can be formed which would be in any measure entitled to confidence. After we had dined we retraced our two last courses, and succeeded in ascending the cliff at the place which one of the hunters had pointed out, taking, without the least regret, our final leave of the "valley of the souls in purgatory."[47] From the brow of the perpendicular precipice, an ascending slope of a few rods conducted us through scattering groves of junipers, to the border of the open plain. Here the interminable expanse of the grassy desert burst suddenly upon our view. The change was truly grateful. Instead of a narrow crooked avenue, hedged in by impending cliffs and frightful precipices, a boundless and varied landscape lay spread before us. The broad valley of the Arkansa, studded with little groves of timber, and terminated in the back ground by the shining summit of James's Peak, and numerous spurs of the Rocky Mountains, with the snowy pinnacles of the more distant ranges, limited our view on the right; on our left, and before us, lay the extended plain, diversified with vast conic mounds, and insulated table-like hills, while herds of bisons, antelopes, and wild horses, gave life and cheerfulness to the scene.