Our course, which was a little east of south, led us across several extensive valleys, having a thin dark coloured soil, closely covered with grasses, and strewed with fragments of greenstone. Descending towards evening into a broad and deep valley, we {269} found ourselves again immured between walls of grey sandstone, similar in elevation and all other particulars to those which limit the valley of Purgatory Creek. It was not until considerable search had been made, that we discovered a place where it was possible to effect the descent, which was at length accomplished, not without danger to the life and limbs of ourselves and horses. The area of the valley was covered with a sandy soil. Here we again saw the great cylindric cactus, the cucumis, and other plants common to the sandy districts, but rarely found in the scanty soils of the fletz trap formation. Pursuing our way along this valley, we arrived towards evening at an inconsiderable stream[51] of transparent and nearly pure water, descending along a narrow channel paved with black and shapeless masses of amygdaloidal and imperfectly porphyritic greenstone. This was the first stream we had for a long time seen traversing rocks of the secondary formation, whose waters were free of an impregnation of muriate of soda and other salts. From the very considerable magnitude of the valley, and the quantity of water in the creek, it is reasonable to infer that its sources were distant at least twenty miles to the west, and the purity and transparency of its waters afford sufficient evidence that it flows principally from a surface of trap rocks. Having crossed the creek with some difficulty, we halted on its bank to set up our tent, and prepare ourselves for a thunder shower, which was already commencing. After the rain, the sky became clear, and the sun, which was near setting, gilded with its radiance the dripping foliage of a cluster of oaks and poplars, which stood near our tent. The grassy plain, acquiring an unwonted verdure from the shower, and gemmed with the reflection of innumerable pendant rain-drops, disclosed here and there a conic pile, or a solitary fragment of black and porous amygdaloid. The thinly-wooded banks of the creek {270} resounded to the loud notes of the robin, and the more varied and melodious song of the mocking-bird; the stern features of nature, which we had long contemplated with a feeling almost of terror, seemed to relax into a momentary smile to cheer us on our toilsome journey.