A few minutes later Fenn had come upon the object of his search. The spring gushed out from the side of a hill, and so strong was the sulphur that the stones, over which the spring, and the stream resulting from it, flowed were a yellowish white.
"Whew!" exclaimed Fenn again. "This ought to be good for whatever ails you, but I don't like it."
He remained looking at the spring for a few minutes, and, as he was about to move away he was startled by a deep, booming sound in the woods, off to his left. Fenn started.
"Blasting?" he exclaimed aloud, in a questioning tone. "No, it can't be that, either," he added. "They wouldn't be blasting around here!"
The next moment he heard a pattering around him, and several large globules of mud came down, seemingly from the sky. Some struck on his hands, and others dotted the white snow about him.
"That's queer," murmured the lad. "It's raining mud--or else--" he paused a moment, as the remembrance of the booming sound returned to him. "No," he added, "there must be a spouting, boiling spring around here. That's what it is! I'm on the track of it now."
Fenn dashed off to the left, through the forest. He was eager to see what had caused the curious shower of mud. In a few minutes he came to a little clearing in the woods--a clearing remarkable, among other things, from the fact that the ground there was devoid of snow. There was a warm, damp look about it, too, as when, in a snow storm, the sidewalk over a bakery oven is devoid of the white flakes.
But that was not the most curious thing that met Fenn's eyes. He made out numerous mud turtles crawling about over the patch of ground that was free from snow. There must have been a score of the reptiles.
Then, as Fenn looked, a curious thing happened. He had just noted that, in the centre of the clearing, there was a large patch of water, and, a moment later the middle of this spring seemed to lift itself bodily up. Up and up the water spouted, and in an instant its comparative purity was changed to a deep mud color, as a miniature geyser of earth and liquid shot upward.
"A mud volcano!" exclaimed Fenn, as he understood what the phenomenon was. "A mud volcano! This explains the mystery of the turtles!"
