The abyss was always the same, yet with colossal variety:  here and there yawnings of veined precipices, followed by cavernous closings of the awful sides; breakings in of subsidiary canons, some narrow clefts, and others gaping shattered mouths; the walls now presenting long lines of rampart, and now a succession of peaks.  But still, although they had now traversed the chasm for seventy or eighty miles, they found no close and no declension to its solemn grandeur.

At last came another menace, a murmur deeper and hoarser than that of the rapid, steadily swelling as they advanced until it was a continuous thunder.  This time there could be no doubt that they were entering upon a scene of yet undecided battle between the eternal assault of the river and the immemorial resistance of the mountains.

The quickening speed of the waters, and the ceaseless bellow of their charging trumpets as they tore into some yet unseen abyss, announced one of those struggles of nature in which man must be a spectator or a victim.

CHAPTER XXVII.

As Thurstane approached the cataract of the San Juan he thought of the rapids above Niagara, and of the men who had been whirled down them, foreseeing their fate and struggling against it, but unable to escape it.

“We must keep near one wall or the other,” he said.  “The middle of the river is sure death.”

Paddling toward the northern bank, simply because it had saved them in their former peril, they floated like a leaf in the shadows of the precipices, watching for some footway by which to turn the lair of the monster ahead.

The scenery here did not consist exclusively of two lofty ramparts fronting each other.  Before the river had established its present channel it had tried the strength of the plateau in various directions, slashing the upper strata into a succession of canons, which were now lofty and arid gullies, divided from each other by every conceivable form of rocky ruin.  Rotundas, amphitheatres, castellated walls, cathedrals of unparalleled immensity, facades of palaces huge enough to be the abodes of the principalities and powers of the air, far-stretching semblances of cities tottering to destruction, all fashions of domes, towers, minarets, spires, and obelisks, with a population of misshapen demons and monsters, looked down from sublime heights upon the voyagers.  At every turn in the river the panorama changed, and they beheld new marvels of this Titanic architecture.  There was no end to the gigantic and grotesque variety of the commingling outlines.  The vastness, the loneliness, the stillness, the twilight sombreness, were awful.  And through all reverberated incessantly the defiant clarion of the cataract.

The day was drawing to that early death which it has always had and must always have in these abysses.  Knowing how suddenly darkness would fall, and not daring to attempt the unknown without light, the travellers looked for a mooring spot.  There was a grim abutment at least eighteen hundred feet high; at its base two rocks, which had tumbled ages ago from the summit, formed a rude breakwater; and on this barrier had collected a bed of coarse pebbles, strewn with driftwood.  Here they stopped their flight, unloaded the boat and beached it.  The drift-wood furnished them a softer bed than usual, and materials for a fire.