Once more the odd booming sound was borne to Ralph’s ears. It came from off to his left. The mud fell again in showers all about him.

“It’s some sort of a boiling spring!” exclaimed Ralph suddenly. “I’ll bet a doughnut that’s what it is. What a chump I was to think that the man on the rock had anything to do with it. Yet it did give me a scare for a minute, too.”

He dashed off in the direction of the booming sound, eager to see what he was certain now had caused the shower of mud. He soon came upon it. In a little clear space amidst the pines he found himself in marshy ground. Rank green grass and flowers of bright colors grew here, and brilliantly colored dragon-flies shot hither and thither through the moist, warm air. The atmosphere[115] held a steamy, unwholesome sort of dampness.

Suddenly there came a rumbling sound which quickly changed to a roar like that of a locomotive blowing off steam, and from the center of the clearing there shot up a clear stream of steaming water. But in a flash its purity was sullied and it turned a dark muddy color. The rumbling increased in violence and a miniature geyser of mud and steaming hot water was shot upward to a considerable height.

Ralph made a swift dash for the shelter of a Douglas fir and looked on curiously while the convulsion of nature lasted. Then he ventured out to examine the geyser more closely. To his disappointment he found that he could not approach the depression from which the mud and water had been spouted upward. The ground was far too swampy to permit such a proceeding and the boy was compelled to look on at the strange sight from a distance.

[116]

The convulsions occurred with almost clock-like regularity, at intervals of about ten minutes. As he watched, Ralph thought of the professor, and how delighted the man of science would have been to behold such a sight. He made careful mental notes of the operations of the mud geyser, however, so that he could be sure to give an accurate account of it to the professor when he returned.

Suddenly, behind him, he heard an odd, rustling sort of noise and noticed a movement in the tall grass. He parted the vegetation to see what could be causing the disturbance. The next instant he leaped backward with a spring that would have done credit to a gymnast.

He had almost stepped on a huge rattlesnake that was coiled in the grass. All at once he became aware that in his backward spring he had nearly landed on another of the reptiles, a snake fully five feet in length. This caused the boy to beat a precipitate retreat, choosing open ground[117] for the purpose. It was not till then that he began to notice that the entire vicinity of the hot springs was fairly alive with the scaly reptiles. Undoubtedly they had been attracted there by the warmth of the ground and had a den in the neighborhood.

“Ugh!” exclaimed the boy with a shudder, “I never did like snakes. I guess I’ll get out of this as quickly as possible. Some of those fellows beat anything I saw in Arizona. I don’t fancy their company.”

He retraced his steps to the point where he had left the trail of the missing ponies and took it up once more. It led down into the valley and Ralph, thinking of the scores of serpents that must haunt the vicinity of the geyser, followed it with a thankful feeling that he had seen the rattlers in time to avoid them.

The traveling down the side of the ridge on which he was now was almost as hard as his clamber up the opposite acclivity. To make matters[118] worse he encountered several muskegs smelling strongly of sulphur, and undoubtedly fed by the sulphurous springs higher up the hill. But the boy was grateful for one thing that the softer ground did for him. It made the traveling harder, but, at the same time, it held the prints of the runaways’ hoofs as clear as day; and as well as Ralph could judge from the look of their prints they were fairly fresh, and told him that he could not be far from the strays.

This encouraged him greatly, and he made good time down the hillside, strewn though the way was with obstacles. He was traveling forward thus, when from a patch of flowering shrubs ahead there came a rustle and a crackling.

Ralph’s heart jumped into his mouth. Mountain Jim had declared that the ponies had been scare............