Starting, apparently, from the neighborhood of this crater, there came down the mountain a second very narrow and very deep gorge, whose waters, when there were any, emptied into the stream we had been following; the two cañons being separated by a high, narrow rib of rock—a mere wedge. Curiously enough, however, this second cañon did not carry a stream, though we could see the shimmer of two or three pools as they caught the reflection of the sky down there in the bottom of its gloomy depths.
"Well, Dick," said I, "I don't see any sign yet of a pathway up to the top of this 'island' of yours. This basin is merely an enlargement of the cañon; the walls are just as high and just as straight-up-and-down as ever."
"Yes, I see that plainly enough," replied Dick. "Yet there must be a way up somewhere. Those pack-trains didn't come down here for nothing. We shall find a break in the wall presently—up in that gorge, there, it must be, too. So let us go on. Hark! What's that?"
We sat still and listened. The whole atmosphere seemed to vibrate with a low hum, the cause of which we could not understand. It kept on for five minutes, perhaps, and then died out again.
"What was it, Dick?" said I. "Wind?"
"I suppose it must have been," replied my companion; "though there isn't a breath stirring down here. If the sky had not been so perfectly clear all morning I should have said it was a flood coming. It must have been wind, though, I suppose."
Satisfied that this was the cause, we thought no more of it, but, taking up the trail once more, we followed it down to the mouth of the second cañon, and there at the edge of the watercourse all trace of it ceased.
"That seems to settle it," remarked Dick. "You see, Frank, the walls of this cañon are so steep and its bed is so filled with great boulders that even a burro could get no further. The copper must have been carried down to this point on men's backs, and if so, it was not carried any great distance probably. The mine must be somewhere pretty near now; we shan't have to search much further, I think, for a way up this right-hand cliff. Let us unsaddle here, where the horses can get plenty of grass, and go on up on foot."
The ascent of the chasm was no easy task, we found, but, weaving our way between the boulders which strewed its bed, up we went, until presently we came to a place where some time or another a great slice of the wall, about an eighth of a mile in length, falling down, had blocked it completely, forming an immense dam nearly a hundred feet high. It must have been many years since it fell, for its surface was well grown up with trees, though none of them were of any great size. It seemed probable, too, that the base of the dam must be composed of large fragments of rock, for, though there was no stream in the bed of the gorge, it was very plain that water did sometimes run down it. If so, however, it was equally plain that it must squeeze its way through the crevices between the foundation rocks, for there was no sign at all that it had ever run over the top.