After passing the region of inclined sandstone, which is about two miles in width, they began to rise upon what may be considered the base of the mountain. As the day advanced, the heat became oppressive, and they found themselves somewhat exhausted before they had crossed the sandstone hills, which appeared so inconsiderable from our encampment, that the labour of crossing them had been almost forgotten in estimating the toils of the day. The first range of primitive rocks they found far more abrupt and rugged than what they had already passed. Its sides are destitute of vegetation, except a few prickly {192} pears and yuccas, with here and there a stinted oak or juniper, and so steep that great exertion as well as the utmost caution, are necessary in ascending. The rock is an aggregate of felspar and hornblende, approaching in character some of the common varieties of sienite. On the eastern side, where the felspar is in the greatest proportion, it is flesh-coloured, and its structure crystalline; the fractured surface of the mass being uneven like that of coarse granite. Advancing towards the west, hornblende was found to become more and more predominant, and so arranged as to have in the mass a laminated appearance. The natural fissures or cleavages between the lamina run nearly in a perpendicular direction, giving the rock the columnar structure of trap or greenstone. As the detachment proceeded, a few interesting insects and plants occurred to reward their labours. But these impenetrable and naked rocks, are the abodes of few living beings, either animal or vegetable. In the crevices of the rocks where a scanty soil has accumulated, is here and there planted a hardy evergreen, whose short and gnarled trunk, recurved and inflexible branches, proclaim the storms it has withstood, and the centuries during which it has vegetated.