Five o'clock supper left a good margin of day, in which my thoughts reverted to the cañon. I watched the purple shadows stealing out of their caverns and rolling up about the base of the mesas. Jones came over to where I stood, and I persuaded him to walk with me along the rim wall. Twilight had stealthily advanced when we reached the Singing Cliffs, and we did not go out upon my promontory, but chose a more comfortable one nearer the wall. The night breeze had not sprung up yet, so the music of the cliffs was hushed. "You cannot accept the theory of erosion to account for this chasm?" I asked my companion, referring to a former conversation. "I can for this part of it. But what stumps me is the mountain range three thousand feet high, crossing the desert and the cañon just above where we crossed the river. How did the river cut through that without the help of a split or earthquake?" "I'll admit that is a poser to me as well as to you. But I suppose Wallace could explain it as erosion. He claims this whole western country was once under water, except the tips of the Sierra Nevada mountains. There came an uplift of the earth's crust, and the great inland sea began to run out, presumably by way of the Colorado. In so doing it cut out the upper cañon, this gorge eighteen miles wide. Then came a second uplift, giving the river a much greater impetus toward the sea, which cut out the second, or marble cañon. Now as to the mountain range crossing the cañon at right angles. It must have come with the second uplift. If so, did it dam the river back into another inland sea, and then wear down into that red perpendicular gorge we remember so well? Or was there a great break in the fold of granite, which let the river continue on its way? Or was there, at that particular point, a softer stone, like this limestone here, which erodes easily?" "You must ask somebody wiser than I." "Well, let's not perplex our minds with its origin. It is, and that's enough for any mind. Ah! listen! Now you will hear my Singing Cliffs." From out of the darkening shadows murmurs rose on the softly rising wind. This strange music had a depressing influence; but it did not fill the heart with sorrow, only touched it lightly. And when, with the dying breeze, the song died away, it left the lonely crags lonelier for its death. The last rosy gleam faded from the tip of Point Sublime; and as if that were a signal, in all the clefts and cañons below, purple, shadowy clouds marshaled their forces and began to sweep upon the battlements, to swing colossal wings into amphitheaters where gods might have warred, slowly to enclose the magical sentinels. Night intervened, and a moving, changing, silent chaos pulsated under the bright stars. "How infinite all this is! How impossible to understand!" I exclaimed.