"What is it then?" demanded Tom.
Jim listened for a moment. There was no denying the sound. It was different from the roar of the river. A deep rumbling bass with a grinding sound to it.
"I know what it is!" he cried. "It is the big boulders at the bottom of the river being rolled along by the current."
"Think of the force of it," I exclaimed. "I bet they are as big as a horse."
"Nearer an elephant!" cried Jim.
There was something appalling in a power that could play marbles with huge rocks.
"That's what helps to cut these gorges," said Jim.
I can give no adequate idea of this canyon. It was wonderful. In some places the walls were so perpendicular that they seemed to bend over us. But you must not imagine that the walls were all alike, and always perpendicular. For this was not so.
There was a wonderful variety. There were rounded summits of rocks standing back from the river giving the effect of their full majesty.
The walls averaged nearly three thousand feet. The prevailing color was the red sandstone but there would be broad bands of grey. Towards the lower end the walls were shattered into thousands of pinnacles rising in their piercing splendor towards the blue above.