We marched, thus without halting for about a week along the hills, during which the mountain chains on the west of the Puerco constantly drew nearer to us and contracted the valley. We had followed our course one whole morning without finding water, till about two o'clock p.m., when the heat became unendurable, and we looked out ahead for some shadow in which we could rest for a few hours. At length we caught sight of a clump of trees, and to our indescribable joy we saw distinctly that they were poplars which retained their fresh foliage, an infallible sign that there was water near; for such trees often stand in pools, and when the water dries up their leaves turn yellow and fall off. We urged our cattle on in order to reach the trees as speedily as possible, for now that we might expect shadow, and probably water, we felt the sun's heat doubly. On these plains objects are seen so clearly and distinctly for incredible distances, that you often deceive yourself, and such was the case with these poplars; we constantly believed that we must reach them in a quarter of an hour, and yet hours passed ere we really arrived. We hastened into the thick shade of the old trees, and I can scarce describe the cheerful feeling that possessed us all on seeing close to them, instead of a pool of muddy slime, two ponds of the clearest, freshest spring water, one of which the poplars overshadowed with their long branches. The cattle were quickly unloaded, and rolling themselves on the grass they dried their wet backs, while we, reclining on the turf, inhaled the cooler air. The pools, like the mountain-springs near my house, had no visible connexion with any other water, but for all that retained their freshness, though almost constantly exposed to the burning sun.