We observed about this camp, a yellow-flowering sensitive plant, apparently a congener to the saw-brier, (schrankia uncinata) of the Platte and Arkansa. Its leaves are twice pinnated, and manifestly irritable. We also added to our collection, two new species of gaura, smaller than G. mollis, which is also found here.
Several rattle-snakes were seen, and many orbicular lizards. These are evidently of two different species, differing from each other in the length of the spines and position of the nostrils. Scarce any two of either species are precisely similar in colour, but the markings are permanent. Both species possess, in a slight { 277} degree, the power of varying the shades of colour. We can find no conspicuous difference, marking the different sexes in the species with long spines; the other we have not had sufficient opportunity to examine.
Wednesday, August 2d. The rain which had fallen during great part of the preceding day and night, had considerably raised the water in the small creek on which we were encamped. At sunrise we collected our horses and proceeded down the valley, the direction of our course south, 30° east. At the distance of two or three miles we found the valley much expanded in width, and observed a conspicuous change in the sandstone precipices which bound it. This change is the occurrence of a second variety of sand-rock, appearing along the base of the cliff, and supporting the slaty argillaceous stratum already described. These rocks have precisely the same position relative to each other, and nearly the same aggregate elevation, as the two very similar varieties observed in the valley of Purgatory creek; indeed, the conclusion that they are the continuation of the same strata as appeared similarly exposed in that valley, can scarcely be avoided. The lowermost, or red sand-rock, is here very friable and coarse. Its prevailing colour is a yellowish grey or light brown. It is often made up almost exclusively of large rounded particles of white or transparent quartz, united by a scanty cement, which usually contains lime, and sometimes, but not always, oxide of iron. In some instances the cement seems to be wanting. Its stratifications are very indistinct compared to those of the gray sandstone, and like them disposed horizontally.