The plateau where their ponies were cropping the grass was several acres in extent, nearly half of it sloping abruptly; but the grass was abundant enough to furnish the animals with all they could need, no matter how long they stayed, since it had plenty of opportunity to renew itself. Side by side the boys moved across the space, the ponies not raising their heads to look at them, as they passed near. Instead of following the course taken by their guide they bore to the right, but at the same time proceeded nearly westward, which led them deeper into the mountains. Remembering the caution of their friend they studied the landmarks around them, in the hope of not losing their way when it should become time to return to camp. When fairly clear of the plateau, where they must have been at a considerable elevation above the sea, they found the way so rough that travelling became a task. There was nothing in the nature of a path or trail to follow, and they were compelled to pass around boulders and rocks, sometimes turning back and retracing their steps, and making long detours, so as to flank impassable chasms. All this tended to confuse their knowledge of the points of the compass, but they did not forget to note everything that could serve as a guide, and were confident of finding their way whenever it should become necessary to return. Most of the time Jack Dudley was in the lead, for it was not easy to walk beside each other. He was perhaps a half-dozen paces in advance of Fred, when he abruptly stopped with an exclamation of affright. "What is it?" asked his friend, hardly less startled. "Look at that!" He pointed downward, almost at his feet. Still unaware of what he meant, Fred stepped guardedly forward to his side. There was good cause, indeed, for the alarm of the elder, for he had checked himself on the edge of a ravine or canyon fully a thousand feet deep. One step further and he would have dropped into eternity. The peculiar formation of the canyon accounted for this peril. The chasm was barely a dozen feet wide, but the other side was depressed, so that it was not noticed by the youth until on the edge of the danger. The walls were of solid rock, showing the numerous strata of sandstone and other formations, worn so unevenly that it looked possible for a person to use them as stairs in climbing the sides. Pausing on the edge and peering cautiously down the dizzy steep, the youths could see a stream of water, winding its course far down at the bottom, where the roughness of its bed churned it into foam, and gave it the appearance of a white ribbon that had been strung along the course. The murmur was so soft and faint that at times they were not sure they heard it, and when it reached their ears the voice of the distant ocean was suggested.