As a matter of fact, Dad had led them into new fields.  But at last they stood upon the surer foundation of the bottom of the chasm.

“Anyone needs to be a mountain goat to take that journey,” said Tad, with a laugh.

“No, a bird would be better,” piped Stacy.

“I’d rather be a bug, then I wouldn’t have to climb,” spoke up Walter.

“Hurrah!  Walt’s said something,” shouted Ned.

By this time Nance and the Professor had walked along, climbing over boulders, great blocks of stone that had tumbled from the walls above, making their way to the edge of the river.

The others followed, talking together at the tops of their voices, laughing and joking.  They felt relieved that the terrible climb had come to an end.  As they approached the river, their voices died away.  It was a sublime but terrifying spectacle that the Pony Rider Boys gazed upon.

“This is more wonderful than Niagara,” finally announced the Professor.  “The rapids of the Niagara River would be lost in this turbid stream.”

Great knife-like rocks projected from the flood.  When the water struck these sharp edges it was cleanly cut, spurting up into the air like geysers, sending a rainbow spray for many yards on either side.

What puzzled the lads more than all else were the great leaping waves that rose without apparent cause from spaces of comparatively calm water.  These upturning waves, the guide explained, were the terror of explorers who sought to get through the Canyon in boats.

“Has any one ever accomplished it?” asked Tad.

“Yes; that intrepid explorer, Major J.W.  Powell, made the trip in the year 1869, one of the most thrilling voyages that man ever took.  Several of his men were lost; two who managed to escape below here were killed by the Indians.”

“I think I should like to try it,” said Tad thoughtfully.

“You won’t, if I have anything to say about the matter,” replied Dad shortly.

“No one would imagine, to gaze down on this stream from the rim, that it was such a lively stretch of water,” remarked the boy.  “It doesn’t seem possible.”

“Yes, if they had some of this water up on the plateau it would be worth almost its weight in gold,” declared Nance.  “Water is what Arizona needs and what it has precious little of.  Speaking of the danger of the river,” continued Nance, “it isn’t wholly the water, but the traveling boulders.”

“Traveling boulders!” exclaimed the boys.

“Yes.  Boulders weighing perhaps a score or more of tons are rolled over and over down the river by the tremendous power of the water, almost with the force and speed of projectiles.  Now and again they will run against snags.  The water dashing along behind them is suddenly checked under the surface.  The result is a great up-wave, such as you have already observed.  They are just as likely to go downward or sideways as upward.  You never know.”