"Look at 'em.

See me hit that one." He pitched down a large piece of stone as he spoke, and I saw something glide into a crevice, while another reptile raised itself up against a piece of rock and fell back hissing angrily.
We were so high up that I could not tell how big these creatures were, but several that we noticed must have been six or seven feet long, and like many vipers of the poisonous kinds, very thick in proportion.
I daresay we should have stopped there amusing ourselves for the next hour, pitching down stones and making the vipers vicious; but our childish pursuit was ended by the doctor, who clapped Jack on the shoulder.
"Come, Jack," he said, "if we leave you there you'll fall asleep and topple to the bottom." Jack drew up his legs and climbed once more to his feet, looking very hot and languid, but he shouldered his piece and stepped out as we slowly climbed along the edge of the chasm for about a quarter of a mile, when it seemed to close up after getting narrower and narrower, so that we continued our journey on what would have been its farther side had it not closed.
Higher and higher we seemed to climb, with the path getting more difficult, save when here and there we came upon a nice bare spot free from stones, and covered with a short kind of herb that had the appearance of thyme.
But now the heat grew less intense.

Then it was comparatively cool, and a soft moist air fanned our heated cheeks.

The roar of the falls grew louder, and at any moment we felt that we might come upon the sight, but we had to travel on nearly half a mile along what seemed to be a steep slope.

It was no longer arid and barren here, for every shelf and crevice was full of growth of the most vivid green.