There _was_ a trail, as we soon perceived; and, what was more significant, one that had recently been travelled! Horses had been over it; and in several places the rocky pebbles, that should otherwise have been dry, were wet by the water that had dripped from their fetlocks. A large troop of horses must have passed just before us. Had the dragoon escort gone that way? More likely a party of mounted travellers belonging to the train? And yet this did not strike us as being likely. We were soon convinced that such was not the case. On riding forward, we came upon a mud-deposit--at the mouth of one of the transverse ravines--over which led the trail. The mud exhibited the _tracks_ distinctly and in a more significant light--they were _hoof-tracks_! We saw that more than a hundred horses had passed up the defile; and not one _shod_ animal among them! This fact was very significant. They could not have been troop-horses? Nor yet those of white men? If ridden, they must have been ridden by Indians? It did not follow that they were ridden. We were travelling through a region frequented by the _mustang_. Droves had been seen upon our route, at great distances off: for these are the shyest and wildest of all animals. A _caballada_ may have passed through the gorge, on their way to the upper valley? There was nothing improbable in this. Although the plains are the favourite habitat of the horse, the _mustang_ of Spanish America is half a mountain animal; and often penetrates the most difficult passes-- climbing the declivities with hoof as sure as that of a chamois. Had these horses been ridden? That was the point to be determined, and how? The sign was not very intelligible, but sufficiently so for our purpose. The little belt of mud-deposit was only disturbed by a single line of tracts--crossing it directly from side to side. The animals had traversed it in single file. Wild horses would have _crowded over it_-- some of them at least kicking out to one side or the other? This I myself knew. The reasoning appeared conclusive. We had no longer a doubt that a large party of Indians had gone up the gorge before us, and not very long before us. It now became a question of advance or retreat. To halt within the defile--even had a halting-place offered--would have been perilous above all things. There was no spot, where we could conceal either ourselves or our animals. The mounted Indians might be returning down again; and, finding us in such a snug trap, would have us at their mercy? We did not think, therefore, of staying where we were. To go back was too discouraging. We were already half through the canon, and had ridden over a most difficult path--often fording the stream at great risk, and climbing over boulders of rock, that imperilled the necks, both of ourselves and our animals. We determined to keep on.